Download Chapter 19 The theory of effective demand

Chapter 19
The theory of effective demand
In essence the “Keynesian revolution” was a shift of emphasis
from one type of short-run equilibrium to another type as providing the appropriate theory for actual unemployment situations.
−Edmund Malinvaud (1977), p. 29.
In this and the following chapters the focus is shifted from long-run macroeconomics to short-run macroeconomics. The long-run models concentrated
on factors that are important for the economic evolution over a time horizon
of at least 10-15 years. With such a horizon it is the development on the supply side (think of capital accumulation, population growth, and technological
progress) that is the primary determinant of cumulative changes in output
and consumption − the trend. The demand side and monetary factors are
important for the fluctuations about the trend. In a long-run perspective
these fluctuations are generally considered of only secondary quantitative
importance. But within shorter horizons, they are the focal point and this
brings the demand-side, monetary factors, market imperfections, nominal
rigidities, and expectation errors to the fore. The present and subsequent
chapters deal with the role of these short- and medium-run factors.
This chapter introduces building blocks of Keynesian theory for the short
run. The basic concept of effective demand is presented. We take up the
Keynesian criticism of pre-Keynesian (Walrasian) macroeconomic theory for
not distinguishing systematically between ex ante demand and supply on the
one hand and actual transactions on the other. Attention to this distinction
leads to a refutation of Say’s law. Next some microfoundation for the notion
of nominal price stickiness is presented, in particular the menu cost theory.
We also address the conception of “abundant capacity” as the “normal” state
of affairs in an industrialized economy.
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
In the last sections of the chapter we revisit the conventional static ISLM model, well-known from elementary macroeconomics. Keynesian tenets
known as spending multipliers, the balanced budget multiplier, the paradox of
thrift, and the liquidity trap are surveyed. This will serve as an introduction
to dynamic versions of the IS-LM model with endogenous forward-looking
expectations, presented in subsequent chapters.
Until further notice we shall use the term “Keynesian theory” in a broad
sense as denoting a macroeconomic framework dealing with states of the
economy where output and employment are in the main determined by aggregate demand and involuntary unemployment is present. Whether a particular building block in this framework comes from Keynes himself, post-war
Keynesians, or New Keynesians of some sort is not our concern here.
19.1
Stylized facts about the short run
The idea that prices of goods and services are sticky in the short run rests on
the empirical observation that in the short run firms in the manufacturing
and service industries typically let output do the adjustment to changes in
demand while keeping prices unchanged. In industrialized societies firms are
able to do that because under “normal circumstances” there is “abundant
production capacity” available in the economy. Three of the most salient
short-run features that arise from macroeconomic time series analysis of industrialized market economies are the following (cf. Blanchard and Fischer,
1989, Nishimura, 1992, Christiano et al., 1999):
1) Shifts in aggregate demand (induced by sudden changes in the state
of confidence, exports, fiscal or monetary policy, or other events) are
largely accommodated by changes in quantities rather than changes in
nominal prices − nominal price insensitiveness.
2) Large movements in quantities are often associated with little or no
movement in relative prices − real price insensitiveness. The real wage,
for instance, exhibits such insensitiveness in the short run.
3) Nominal prices are sensitive to general changes in input costs.
These stylized facts pertain to final goods and services. It is not the
case that all nominal prices in the economy are in the short run insensitive
vis-a-vis demand changes. One must distinguish between production of final
goods and services on the one hand and production of primary foodstuff and
raw materials on the other. This leads to the associated distinction between
“cost-determined” and “demand- determined” prices.
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Final goods and services are typically differentiated goods (imperfect substitutes). Their production takes place under conditions of imperfect competition. As a result of existing reserves of production capacity, generally
speaking, the production is elastic w.r.t. demand. An upward shift in demand tends to be met by a rise in production rather than price. The price
changes which do occur are mostly a response to general changes in costs of
production. Hence the name “cost-determined” prices.
For primary foodstuff and many raw materials the situation is different.
To increase the supply of most agricultural products requires considerable
time. This is also true (though not to the same extent) with respect to
mining of raw materials as well as extraction and transport of crude oil.
When production is inelastic w.r.t. demand in the short run, an increase
in demand results in a diminution of stocks and a rise in price. Hence the
name “demand-determined prices”. The price rise may be enhanced by a
speculative element: temporary hoarding in the expectation of further price
increases. The price of oil and coffee − two of the most traded commodities
in the world market − fluctuate a lot.1 Through the channel of costs the
changes in these demand-determined prices spill over to the prices of final
goods.
As macroeconomics by and large deals with industrialized economies,
where manufacturing and services are the main sectors, the general price
level is typically regarded as cost-determined rather than demand determined. Two further aspects are important. First, many wages and prices are
set in nominal terms by price setting agents, say, craft unions and firms operating in imperfectly competitive markets. Second, these wages and prices
are in general deliberately kept unchanged for some time even if changes
in the environment of the agent occurs; this aspect, interpreted as reflecting the presence of pecuniary as well as non-pecuniary costs associated with
changing prices, is called nominal price stickiness. Both aspects have vast
consequences for the functioning of the economy as a whole compared with
a regime of perfect competition and flexible prices.
19.2
A simple short-run model
The simple model presented below is close to what Paul Krugman named
the World’s Smallest Macroeconomic Model.2 The model is useful in at least
three ways:
1
2
See, e.g., Fig. 15.1 in Chapter 15.
Krugman (1999). Krugman tells he learned the model back in 1975 from Robert Hall.
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
• the model demonstrates the fundamental difference in the functioning
of an economy with flexible prices and one with sticky prices;
• the model is a suitable point of departure for a definition of the Keynesian concept of effective demand;
• the model displays the logic behind the Keynesian refutation of Say’s
law.
19.2.1
Elements of the model
We consider a monetary closed economy which produces a consumption good.
There are three sectors in the economy, a production sector, a household
sector, and a public sector with a consolidated government/central bank.
Time is discrete. There is a current period and “the future”, compressing
the second period and onward. Labor is the only input in production. To
simplify notation, the model presents its story as if there is just one representative household and one representative firm owned by the household, but
the reader should imagine that there are numerous agents of each kind.
The production function has CRS,
 = 
  0
(19.1)
where  is aggregate output of a consumption good which cannot be stored,
 is a technology parameter, and  is aggregate employment, both in the
current period. The price of the consumption good in terms of money, i.e.,
the nominal price, is  the wage rate in terms of money, the nominal wage,
is  Suppose the representative firm takes these current prices as given.
The nominal profit is
Π =   −  
(19.2)
There is free exit from the production sector in the sense that the representative firm can decide to produce nothing. Hence, an equilibrium with positive
production requires that profits are non-negative.
The representative household supplies labor inelastically in the amount ̄
and receives the profit obtained by the firm, if any. The household demands
the consumption good in the amount  in the current period. Current income
not consumed is saved for the future. We assume that the only non-human
asset available is fiat money, which is thus the only asset on hand for saving.
There is no private banking sector in the economy. So “money” means the
monetary base (think of currency in circulation) and is on net an asset in
the private sector as a whole. Until further notice the money supply is not
changed.
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The preferences of the household are given by the intertemporal utility
function,
0
0    1
(19.3)
 = ln  +  ln  

Here,  is the utility discount factor (equal to (1 + )−1 if  is the utility
discount rate),  0 is the amount of money transferred to “the future”, and
  is the expected future price level.
Consider the household’s choice problem. Facing  and  and expecting
that the future price level will be    the household chooses  and  0 to
maximize  s.t.
  +  0 =  +   + Π ≡ 
(19.4)
Here,   0 is the stock of money held at the beginning of the current period
and is predetermined. The actual employment is denoted  and equals the
minimum of the amount of employment offered by the firm and the labor
supply, ̄ (the voluntary trade principle). The sum of initial financial wealth,
 and nominal income,   + Π constitutes the budget, 3 Nominal
financial wealth at the beginning of the next period is  0 =  +   +
Π −   i.e., the sum of initial financial wealth and saving where the latter
equals   + Π −   The benefit obtained by transferring  0 depends
on the expected purchasing power of  0  hence it is  0   that enters the
utility function. This minimalist way of taking the future into account is of
course a shortcut.
Substituting  0 =  −   into (19.3), we get the first-order condition

1


= +
(−  ) = 0


 −  
which gives
 =
1

1+
(19.5)
We see that the marginal (= average) propensity to consume is (1 + )−1 
hence inversely related to the patience parameter  The resulting stock of
money held at the end of the period is
 0 = (1 −

1
) =

1+
1+
3
As time is discrete, expressions like  +   + Π are legitimate. Although it is
meaningless to add a stock and a flow (since they have different denominations), the sum
 +   + Π should be interpreted as  + (  + Π)∆ where ∆ is the period length
equal to one time unit.
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
So the expected price level,    in the future does not affect the demands, 
and  0  This is a special feature, due to the additive logarithmic specification
of the utility function in (19.3).
Inserting (19.4) and (19.2) into (19.5) gives

+
 +  + Π

=
= 

=
 (1 + )
 (1 + )
1+
(19.6)
Suppose there is equilibrium in the output market in the sense that  = 
Inserting this into (19.6), we can find  expressed in terms of  :
 =



(19.7)
This is so far no solution for  since also  is an endogenous variable.
We have assumed that agents take prices as given when making their
demand and supply decisions. But we have said nothing about whether
nominal prices are flexible or rigid.
19.2.2
The case of fully flexible  and 
What Keynes called “classical economics” has by later writers been called
“Walrasian macroeconomics” or simply “pre-Keynesian macroeconomics”.
In this theoretical tradition both wages and prices are assumed fully flexible
and all markets perfectly competitive. Both  and  are thus thought to
adjust immediately so as to clear the labor and output markets like in a
centralized auction market. Clearing in the labor market requires
 = ̄
(19.8)
that is, labor demand,  equals the exogenous labor supply, ̄ In view of
the constant returns to scale production function (19.1), this requires that
firms have zero profit. In turn, by (19.1) and (19.2), zero profit requires that
the real wage equals labor productivity:

= 

(19.9)
Given clearing in the labor market, output equals full-employment output,
 = ̄ ≡   
where the superscript “ ” stands for “full employment”. Output and employment are here said to be supply-determined, i.e., determined by the supply of
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production factors, here labor. The profit is Π =    −  ̄ = (  − ̄)
= 0 in view of (19.9) and the definition of   . The condition (19.7) can now
be solved for the equilibrium price level
 =

≡  


(19.10)
where the superscript “” stands for “classical”. This, together with (19.9),
gives the “classical” equilibrium wage
 =   ≡   
(19.11)
General equilibrium also requires that the desired money holding at the
end of the period equals the money supply. By Walras’ law this equality
follows automatically from the household’s Walrasian budget constraint and
equilibrium in the output and labor markets. Indeed, we define the household’s Walrasian budget constraint as given by (19.4) with the employment
term,  interpreted as labor supply, ̄ and the profit term, Π interpreted
as the hypothetical profit calculated on the basis of firms’ desired supply
evaluated at the announced price vector, (  1). Then, for an arbitrary
price vector (  1) with   0 and   0 the values of excess demands
add up to
 ( − ̄) +  ( −  ) +  0 − 
= −Π −  ̄ +   +  0 − 
= −Π −  ̄ +   +  +  ̄ + Π −   −  = 0
where the first equality comes from the definition of Π in (19.2) and the
second from the Walrasian budget constraint. This result reflects that when
households satisfy their Walrasian budget constraints, then the economy as a
whole has to satisfy an aggregate budget constraint for the period in question.
It follows that the equilibrium condition  0 =  is ensured as soon as there
is clearing in the output and labor markets.
Consequently, with (  ) = (     ) there is general equilibrium in this
flexwage-flexprice economy with perfect competition. Such an equilibrium is
called a classical or Walrasian equilibrium. The intuitive mechanism behind
it is the following adjustment process. Imagine that in an ultra-short subperiod  − 6= 0 In case  −  0 ( 0) there will be excess supply
(demand) in the labor market. This drives  down (up). Only when 
=  and full employment obtains, can the system be at rest. Next imagine
that  −   6= 0 In case  −    0 ( 0) there is excess supply (demand)
in the output market. This drives  down (up). Again, only when  =  
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
and  =  (whereby  =   ), so that the output market clears under
full employment, will the system be at rest.
This adjustment process is fictional, however, because outside equilibrium
the Walrasian supplies and demands which supposedly drive the adjustment
are artificial constructs. Being functions only of initial resources and price
signals, the Walrasian supplies and demands are mutually inconsistent outside equilibrium and can therefore not tell what quantities will be traded
during an adjustment process. The story needs a considerable refinement
unless one is willing to let the mythical “Walrasian auctioneer” enter the
scene and bring about adjustment toward the equilibrium prices without
allowing trade until these prices are found.
Anyway, by comparative statics based on (19.10) and (19.11) we see that
in the classical regime,  and  are higher the higher is  Output is at
the unchanged full-employment level whatever the level of . This is the
neutrality of money result of classical macroeconomics.
The neutrality result also holds in a dynamic context where we consider
an actual change in the money supply occurring in historical time. Since by
assumption money is the only asset in the economy, such a change in the
money supply can not be brought about through open market operations
where the central bank buys or sells another financial asset. Instead we
imagine that the government at the beginning of the period brings about
lump-sum transfers to the households in the total amount ∆  0 As
there is no taxation, this implies a budget deficit which we thus assume fully
financed by money issue. So (19.4) is replaced by
  +  0 =  + ∆ +   + Π ≡ 
(19.12)
If we replace  in the previous formulas by ̂ ≡  + ∆ we see that
money neutrality still holds. Now there is nominal private saving of size
  = ∆ +   + Π −   =  0 −  = ∆ On the other hand the
government dissaves, in that its saving is   = −∆ where ∆ is the
government budget deficit. So national saving is and remains  ≡   +  
= 0 (it must be nil as there are no durable produced goods).
19.2.3
The case of sticky  and 
In standard Keynesian macroeconomics nominal wages are considered predetermined in the short run, fixed in advance by wage bargaining between
workers (or workers’ unions) and employers (or employers’ unions). Nominal
prices are also fixed in advance and set by price setting firms facing downward sloping demand curves. It is understood that there is a large spectrum
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713
of differentiated products. This heterogeneity ought of course be visible in
the model − and it will become so in Section 19.3. But at this point the
model takes an easy way out and entirely ignores the involved aggregation
issues.
Let  in the current period be given at the level ̄  Because firms have
market power, the profit-maximizing price involves a mark-up on marginal
cost, ̄  = ̄  (which is also the average cost). We assume that the
price setting occurs under circumstances where the chosen mark-up becomes
a constant   0, so that
 = (1 + )
̄
≡ ̄ 

(19.13)
While ̄ is considered exogenous (not determined within the model), ̄ is
endogenously determined by the given ̄   and 
Because of the fixed wage and price, the different markets may feature
excess demand or excess supply (to be defined more precisely below). According to the principle that no agent can be forced to trade more than
desired, the actual amount traded in a market must equal the minimum of
demand and supply. So in the output market and the labor market the actual
quantities traded are
 = min(     ) and
 = min(     )
(19.14)
respectively, where the superscripts “” and “” denote demand and supply,
respectively. This principle, that the short side of the market determines the
traded quantity, is called the short-side rule. The other side of the market is
said to be quantity rationed or just rationed if there is discrepancy between
  and   .
There are in the present framework two alternative cases − or “regimes”
− to consider plus a border case.
The Keynesian regime: ̄    (1 + )
In view of (19.13), in this regime we must have ̄     ≡   . From the
condition (19.7), we find that the aggregate demand consistent with  =  
is   = ( ̄ ) Firms would loose by producing more than they are able to
sell at their preset price, ̄ . This price is and remains the profit maximizing
price since marginal costs are constant and there is nothing in the situation
to defy the constant mark-up assumption. Actual output will therefore be
 = =


≡ = 
≡  


 ̄
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
where the superscript “” stands for “Keynesian” and the inequality is implied by ̄    .
From (19.1) and the short-side rule now follows that employment is
 =  =


=
 ̄ =   

 ̄
(19.16)
Profits are Π = ̄  − ̄  = (1 − ̄̄ )̄  = (1 − (1 + )−1 ) −1   0 where
we have used, first, (19.1) and then (19.13) and (19.15).
This solution for ( ) is known as a Keynesian equilibrium for the
current period. It is named an equilibrium because the system is “at rest”
in the following sense: (a) agents do the best they can given the constraints
(which include the preset prices and the quantities offered by the other side of
the market); and (b) the chosen actions are mutually compatible (purchases
and sales match). The equilibrium is said to be Keynesian because there is
unemployment and at the same time it is aggregate demand in the output
market, not the real wage, which is the binding constraint on the employment
level. A higher propensity to consume (lower discount factor ) results in
higher aggregate demand,    and thereby a higher equilibrium output,   .
In contrast, lowering the real wage through a higher mark-up,  or a lower
marginal (= average) labor productivity,  does not result in a higher   .
On the contrary,   becomes lower; in view of (19.13) and (19.15), the causal
chain goes via a higher ̄ . Lowering the nominal wage, however, stimulates
   and thereby    via the negative effect on ̄ 4
A compact characterization of the Keynesian regime is thus that it leads
to an equilibrium where output as well as employment are demand-determined.
In the language of the microeconomic theory of quantity rationing we may
say that in the Keynesian equilibrium both the output market and the labor
market are buyers’ markets (sale less than desired). We shall not, however,
categorize the state in the output market as one of “excess supply”. The going price level as well as the output level are in the Keynesian regime entirely
voluntary on the part of the price-setting firms.
The “Keynesian cross” and effective demand The situation is illustrated by the “Keynesian cross” in the (   ) plane shown in Fig. 19.1,
where   =  = (1 + )−1 ( + ̄ ) We see the vicious circle. Output
is below the full-employment level because of low consumption demand; and
4
This latter result does not necessarily go through if the expected price in the future,
  plays a role for the current consumption decision (and at the same time depends on
prices in the current period). Our specification of the utility function, however, rules this
out.

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d
Y M
Y
Yd  P
1 
 M
P 1 
O 45 Yk Y Yf

Figure 19.1: The Keynesian regime (̄   (1 + )  and   given, ̄ fixed).
consumption demand is low because of the low employment. The economy
is in a unemployment trap. Even though at   we have Π  0 and there
are constant returns to scale, the individual firm has no incentive to increase
production because the firm already produces as much as it rightly perceives
it can sell at its preferred price. We also see that here money is not neutral.
For a given  = ̄  and thereby a given  = ̄  a higher  results in
higher output and higher employment.
Although the microeconomic background we have alluded to is a specific
“market power story” (one with differentiated goods and downward sloping
demand curves), the Keynesian cross in Fig. 19.1 is valid for any microeconomic story leading to a fixed ̄    and a fixed ̄  ̄ 
The fundamental difference between the Walrasian and the present framework is that the latter allows trade outside Walrasian equilibrium. In that
situation the households’ consumption demand depends not on how much
labor the households would prefer to sell at the going wage, but on how
much they are able to sell, that is, on a quantity signal received from the
labor market. Indeed, it is the actual employment,  that enters the operative budget constraint, (19.4), not the desired employment as in classical or
Walrasian theory.
On this background Keynesian theory defines a household’s effective budget constraint as the budget constraint conditional on the perceived price
signals and the perceived quantity signals from the markets. These quantity signals are in the present context the employment level offered and the
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
perceived profit to be paid out from the firms. A household’s effective consumption demand is the consumption demand conditional on the effective
budget constraint; the formula (19.6) illustrates this concept. The level of
aggregate effective demand is given by the Keynesian cross in Fig. 19.1 as
 .
The repressed inflation regime: ̄    (1 + )
This regime represents the “opposite” case of the Keynesian regime. In view
of (19.13), we must in this regime have ̄     ≡   . Hence ( ̄ )
 (  ) =   = ̄ In spite of the high demand, combined with a realwage level which does not deter profitable production, the shortage of labor
hinders the firms to produce more than   at the going price. With  =   
output demand, which in this model is always the same as consumption
demand,  is, from (19.6),
 = =

̄
+
  =   =   =  
1+
(19.17)
where   is the realized consumption. We have here defined   to equal
full-employment output,    Thereby consistency with the short-side rule
(19.14) is maintained. Presumably, the excess demand,   −   0 generates pressure for a price increase, but the outcome (19.17) is based on the
assumption that  is sticky so that the price change does not materialize
until possibly the next period. This explains the name repressed inflation.
Fig. 19.2 illustrates.
As the real-wage level does not deter profitable production, the firms’
would like to employ people up to the point where output demand is satisfied,
i.e.,   =    But in view of the short side rule, actual employment will
be

 =   = ̄    =


So there is excess demand in the labor market which presumably will generate
pressure for wage increases. By the assumed nominal wage stickiness, this
does not materialize until possibly the next period.
The equilibrium outcome in the repressed inflation regime is thus ( )
= (   ̄) Consumers are quantity rationed in the goods market, as     
Firms are quantity rationed in the labor market, as    . This is the
background for the parlance that in the repressed inflation regime, output
and employment are not demand-determined but supply-determined.
In the language of the microeconomic theory of quantity rationing we may
say that in contrast to the Keynesian regime, the repressed inflation regime is
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19.2. A simple short-run model
717
Yd M
Y f
P
1 
 Cf  M
Y
Y  P
1 
d
M
P 1 
O 45 Y f
Y 
Figure 19.2: The repressed inflation regime (̄   (1 + )  and   given,
̄ fixed).
characterized by both the output market and the labor market being sellers’
markets (purchase less than desired). Presumably, the repressed inflation
regime will not last long unless possibly in a war situation with wage and
price controls.
The border case between the two regimes: ̄ =   (1 + ) In this
case, by (19.13) follows that ̄ =   . So no market has quantity rationing
and we may speak of both the output market and the labor market as balanced
markets.
There are two differences compared with the classical equilibrium, however. The first is that due to market power, there is a wedge between the real
wage and the marginal productivity of labor. In the present context, though,
where labor supply is inelastic, this does not imply inefficiency but only a
higher profit/wage-income ratio than under perfect competition (where the
profit/wage-income ratio is zero). The second difference compared with the
classical equilibrium is that due to price stickiness, the impact of shifts in
exogenous variables will be different. For instance a lower  will in the
present framework with ̄ =   (1 + ) result in unemployment, while in
the classical model it will just raise  and  and not affect employment.
With effective budget constraints Walras’ law does not hold As we
saw above, with Walrasian budget constraints, the aggregate value of excess
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
demands in the given period is zero for any given price vector, (  1)
with   0 and   0 In contrast, with effective budget constraints the
aggregate value of excess demands is for any given price vector, (  1)
with   0 and   0
 ( − ̄) +  ( −  ) +  0 −  = −Π −  ̄ +   +  0 − 
= −Π −  ̄ +   +  +   + Π −   − 
(19.18)
=  ( − ̄)
where the first equality comes from the definition of Π in (19.2) and the
second from the effective budget constraint, (19.4). We get that Walras’ law
does not hold in a setting where effective budget constraints are operative
rather than Walrasian budget constraints. Consider a state of affairs where
there is clearing in the output market ( =  ) and at the same time actual
money holding ends up equal to desired money holding at the end of the
period ( =  0 ). The result (19.18) tells us that this is compatible with
 6= ̄ Hence clearing in the labor market is not guaranteed. Consider for
instance the Keynesian regime where     and 0     For any such
pair, (  ) we get   ̄ as in Fig. 19.1. According to (19.18), thereby the
aggregate value of excess demands equals  ( − ̄)  0 Equivalently, the
aggregate value of excess supplies is positive. So the positive excess supply
in the labor market need not be accompanied by a presumably expansionary
positive excess demand in the output market. We can only say: If and only
if the labor market clears, then the aggregate value of excess demands equals
zero (a “conditional Walras’ law”).
This takes us to Keynes’ refutation of Say’s law.
Say’s law and its refutation The classical principle “supply creates its
own demand” (or “income is automatically spent on goods”) is named Say’s
law after the French economist and business man Jean-Baptiste Say (17671832). In line with other classical economists like David Ricardo and John
Stuart Mill, but in sharp contrast to the views of Thomas Malthus and
Karl Marx, Say maintained that although mismatch between demand and
production can occur, it can only occur in the form of excess supply in some
industries at the same time as there is excess demand in other industries
− general excess supply of goods is impossible. Or, by another classical
catchphrase:
Whatever the relative prices, every offer to sell a good implies a
demand for some other good.
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19.2. A simple short-run model
719
By “good” is here meant a produced good rather than just any traded article, including for instance money. Otherwise Say’s law would be a platitude
(a simple implication of the definition of trade). So, interpreting “good” to
mean a produced good, let us evaluate Say’s law from the point of view of
the result (19.18). By subtracting  ( − ̄) on both sides of (19.18), we
see that
 ( −  ) +  0 −  = 0
(19.19)
for any   0 Consider the case     and    as in Fig. 19.1. First
of all, the figure illustrates that aggregate demand is rising with aggregate
production. And if aggregate production is in the interval 0       then
 =     ; this amounts to general excess demand for goods and in effect,
by (19.19), excess supply of money. So far Say’s law is not contradicted. But
if instead aggregate production is in the interval         then  =  
  ; now there is general excess supply of goods. Or, which is the same, a
general shortfall of demand. In effect, by (19.19), there is excess demand for
money.
General excess supply of produced goods is thus possible and Say’s law
thereby falsified.5 This is not to deny that a state of affairs with general excess
supply may trigger quantity and/or price responses. Keynes emphasized that
in a modern economy the resulting piles of unsold goods induces firms to cut
production and employment rather than prices. Keynes’ contemporary, A.
C. Pigou, maintained an opposite view namely that the general excess supply
would result in a falling price level, thus leading to higher purchasing power
of  (the “real balance effect”). Anyway, whatever the price response of
the system, it takes time and will thus not occur until the next short period.
We shall therefore categorize it as belonging to dynamic analysis which is
considered in later chapters.
It should be noted that the refutation of Say’s law does not hinge on
money being the asset available for transferring purchasing power from one
period to the next. We may imagine an economy where  represents land
available in limited supply. As land is also a non-produced good, the above
analysis goes through − with one exception, though. The exception is that
∆ in (19.12) can no more be interpreted as a policy choice. Instead, a
positive ∆ could be due to discovery of new land.
5
Keynes’ reasoning (Keynes, 1936) is similar. It might be objected that this “aggregate”
reply to Say’s law is not to the point since Say had a disaggregate structure with many
industries in mind. But considering an explicit disaggregate production sector makes no
essential difference as we shall see towards the end of this chapter.
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
Digging deeper
As it stands the above theoretical framework has many limitations. The
remainder of this chapter outlines how the following problems have been
dealt with in the literature:
(a) The wage and price setting should be explicitly modelled and in this
connection there should be an explanation of the wage and price stickiness.
(b) It should be made clear how to come from the existence of many
differentiated goods and markets with imperfect competition to aggregate
output and income which in turn constitute the environment conditioning
individual agents’ actions.
(c) To incorporate better the role of asset markets, including the primary
role of money as a medium of exchange rather than a store of value, at least
one alternative asset should enter, an interest-bearing asset.
In subsequent chapters we consider a fourth problem:
(d) The model should be truly dynamic with forward-looking endogenous
expectations and gradual wage and price changes depending on the market
conditions, in particular the employment situation.
Let us first consider point (a) and (b).
19.3
Price setting and menu costs
The classical theory of perfectly flexible wages and prices and neutrality of
money treats the wages and goods prices as if they were prices on assets
traded in centralized auction markets. In reality the general price level is
an aggregate of millions of individual prices set by price setters in different
markets and localities. The dominant market form is not perfect competition.
Wage and price setters have market power. And there may be costs associated
with changing prices (and wages).
19.3.1
Imperfect competition with price setters
To understand what determines prices and their sometimes slow response
to changed circumstances, we need a theory with agents who set prices and
decide when to change them and by how much. This brings agents with
market power into the picture and tells us why imperfect competition is a
key ingredient in macroeconomics.6 The challenge is to explain the behavior
6
Under perfect competition all firms are price takers. So who is left to change prices?
This is a sign of a logical difficulty within standard competitive theory (as pointed out by
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19.3. Price setting and menu costs
721
of price-setting suppliers on the basis of their objectives and constraints.
Suppose the market structure is one with monopolistic competition:
1. There is a given large number,  of firms and equally many (horizontally) differentiated products.
2. Each firm supplies its own differentiated product on which it has a
monopoly and which is an imperfect substitute for the other products.
3. A price change by one firm has only a negligible effect on the demand
faced by any other firm.
Another way of stating property 3 is to say that firms are “small” so that
each good constitutes only a small fraction of the sales in the overall market
system. Each firm faces a perceived downward-sloping demand curve and
chooses a price which maximizes the firm’s expected profit, thus implying a
mark-up on marginal costs.7 There is no perceivable reaction from the firm’s
(imperfect) competitors. So the monopolistic competition setup abstracts
from strategic interaction between the firms and is in that respect different
from oligopoly.
With respect to assets, so far our framework corresponds to the World’s
Smallest Macroeconomic Model of Section 19.2 in the sense that there are
no bank-created money and no other non-human assets than base money.
Price setting firms
In the short run there is a given large number,  of firms and equally many
(horizontally) differentiated products. Firm  has the production function 
=   where  is labor input (raw materials and physical capital ignored).8
For notational convenience we imagine measurement units are such that  =
1 Thereby,
1
 =   0   ≤ 1
 = 1 2     
(19.20)
To extend the perspective compared with Section 19.2, the possibility of
rising marginal costs (  1) is now included.
The demand constraint faced by the firm is perceived by the firm to be
µ ¶− 



 =
≡ (    )
  1
(19.21)



Arrow, 1959). To assign the price setting role to abstract “market forces” or an abstract
omnipotent “Walrasian auctioneer” is not a convincing solution.
7
For estimations of the markup in various U.S. industries, see Hall (1988).
8
The following can be seen as an application of the more general framework with pricesetting firms outlined at the end of Chapter 2.
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
where  is the price set by the firm and fixed for some time,  is the
“general price level”,   is the expectation of the overall level of demand in
the economy (this expectation is shared by all firms), and  is the (absolute)
price elasticity of demand (assumed above one since otherwise there is no
finite profit maximizing price).9 So the firm faces a downward sloping demand
curve the position of which is given by the expected general level of demand.
Let firm  choose  at the end of the previous period with a view to
maximization of expected nominal profit in the current period:
max Π =   −  
s.t. (19.21).

Here we may substitute the constraint (19.21) into the profit function and
then solve the unconstrained maximization problem w.r.t.   The more
intuitive approach, however, is to apply the rule that the profit maximizing
quantity of a monopolist (in the standard case with non-decreasing marginal
cost) is the quantity at which marginal revenue equals marginal cost,
 =  =
 1 −1


 
(19.22)
Total revenue is   =   =  ( )  where, from (19.21),
 ( ) =
µ

  
¶− 1

So
 
 0 ( )
1
0
) =  ( )(1 − )
=  ( ) +   ( ) =  ( )(1 +
 =

 ( )

Inserting this into (19.22), we find the expected (or planned) individual output level,   Thereby, the chosen price is
̄ =  ( ) =
1
   1 −1

( )  ≡ (1 + ) ( )  −1 
−1 

(19.23)
where  is the mark-up equal to ( − 1)−1 − 1 = ( − 1)−1 .
This outcome is illustrated in Fig. 19.3 for the case   1 (decreasing
returns to scale). For fixed   and  the demand curve faced by firm  is
shown as the solid downward-sloping curve (    ) to which corresponds
the marginal revenue curve,  For fixed  the marginal costs faced by
the firm are shown as the upward-sloping marginal cost curve,  It is
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19.3. Price setting and menu costs
Pi
723
W , P, Y e , and Yd given
W
1

1
yi 
1

Pi
 Pi d 
,Y 
P

D
 Pi , Y e 

P

D

MC
0
MR
yi e
yi
Figure 19.3: Firm ’s price choice under the expectation that the general demand
level will be   (the case   1). The demand curve for a higher level of general
demand,   , is also shown.
assumed that firm  somehow knows  in advance. The chosen price ̄ is
set optimally in accordance with the  =  rule.
Because of the symmetry, all firms end up choosing the same price, which
therefore becomes the general price level, i.e.,  =   = 1 2. . .  . So
all firms’ expected output level equals the expected average real spending


per consumption good, i.e., P
1 2. . .  . Expectations are
 =    =P
consistent in the sense that (    ) =   =  · (  ) =    If
there are no expectation errors, firm ’s actual output,   equals the expected
output,    As this holds for all  we have in this case
P
X
  X
 ≡ 
=
 =
 =   =   
(19.24)



where   is the actual level of overall demand in the period, that is, actual
aggregate demand.
In some New-Keynesian models the labor market is described in an analogue way with heterogeneous labor organized in craft unions and monop9
Chapter 22 gives an account of the class of consumer preferences that underlie the
constancy of this price elasticity. That chapter also presents a precise definition of the
“general price level“.
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
olistic competition between these. To avoid complicating the exposition,
however, we here treat labor as homogeneous. To put it differently, at this
stage we prefer not to be specific about the modeling of the labor market. No
matter what the details of the labor market are, we shall raise the question:
If aggregate demand in the current period turns out different from expected,
what will the firms do: change the price or output or both? To fix ideas
we will concentrate on the case where the wage level,  is unchanged. In
that case the answer will be that “only output will be adjusted” if one of the
following conditions is present:
(a) The marginal cost curve is horizontal and the price elasticity of demand
is constant.
(b) The perceived cost of price adjustment exceeds the potential benefit.
That point (a) is sufficient for the “only output” answer follows from
(19.23) with  = 1 With rising marginal costs (  1) however, the presence
of sufficient price adjustment costs becomes decisive.
19.3.2
Price adjustment costs
The literature has modelled price adjustment costs in two different ways.
Menu costs refer to the case where there are fixed costs of changing price.
Another case considered in the literature is the case of strictly convex adjustment costs, where the marginal price adjustment cost is increasing in the size
of the price change.
As to menu costs, the most obvious examples are costs associated with
1. remarking commodities with new price labels,
2. reprinting price lists (“menu cards”) and catalogues.
But “menu costs” should be interpreted in a broader sense, including pecuniary as well as non-pecuniary costs of:
3. information-gathering and recomputing optimal prices,
4. conveying rapidly the new directives to the sales force,
5. the risk of offending customers by frequent price changes (in particular
when they are upward),
6. search for new customers willing to pay a higher price,
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19.3. Price setting and menu costs
725
7. rapid renegotiation of contracts.
Menu costs induce firms to change prices less often than if no such costs
were present. And some of the points mentioned in the list above, in particular point 6 and 7, may be relevant also in the different labor markets.
The menu cost theory provides the more popular explanation of nominal
price stickiness. Another explanation rests on the presumption of strictly
convex price adjustment costs. In this theory the cost for firm  of changing
price is assumed to be  =   ( − −1 )2     0 Under this assumption
the firm is induced to avoid large price changes, which means that it tends
to make frequent, but small price adjustments. This theory is related to
the customer market theory. Customers search less frequently than they
purchase. A large upward price change may be provocative to customers and
lead them to do search in the market, thereby perhaps becoming aware of
attractive offers from other stores. The implied “kinked demand curve” can
explain that firms are reluctant to suddenly increase their price.10
Below we describe the role of the first kind of price adjustment costs,
menu costs, in more detail.
The menu cost theory
The menu cost theory originated almost simultaneously in Akerlof and Yellen
(1985) and Mankiw (1985). It makes up the predominant microfoundation
for the presumption that nominal prices and wages are sticky in the short
run. For simplicity, here we shall concentrate on prices and price-setting
firms.
The key theoretical insight of the menu cost theory is that even small
menu costs can be enough to prevent firms from changing their price. This
is because the opportunity cost of not changing price is only of second order,
that is, “small”; this is a reflection of the envelope theorem described in
Appendix A; hence the potential benefit of changing price can easily be
smaller than the cost of changing price. Yet, owing to imperfect competition
(price  MC ), the effect on aggregate output, employment, and welfare of
not changing prices is of first order, i.e., “large”.
As in the World’s Smallest Macroeconomic Model, suppose the aggregate
demand is proportional to the real money supply:
 =
10



For details in a macro context, see McDonald (1990).
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(19.25)
726
CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
where  ∈ (0 1) is a parameter reflecting consumers’ patience. Consider
now firm   = 1 2      contemplating its pricing policy. With actual
aggregate demand given by (19.25), the nominal profit as a function of the
chosen price,   is
Π =   −
1
 
= 
µ


¶−

−

õ


¶−


!1
≡ Π(    )
Suppose that initially,  = ̄  where ̄ is the price that maximizes Π 
given   and ; that is, ̄ is given by (19.23) with  = ( )
Thus, maximum profit in firm  is
Π(̄    ) ≡ Π̄ 
as illustrated in Fig. 19.4.
As noted at the end of Section 19.3.1, the interesting case in relation to
menu costs is the case with rising marginal costs. So we here assume that
  1 In this case a higher  for unchanged  and  will imply higher
̄ (see Exercise 19.??).
Given the price  = ̄ set in advance there is an unexpected shift in
money supply to the level  0   through an unanticipated lump-sum
“helicopter drop” at the beginning of the period.11 Suppose no other agents
respond by changing price, neither price setters nor wage setters. In Fig.
19.4, ̄0 indicates the new price level that would be profit maximizing in the
case of rising marginal costs (  1) and absence of menu costs. Will firm 
have an incentive to change its price to ̄0 ? Not necessarily. The menu cost
may exceed the opportunity cost associated with not changing price. Indeed,
the opportunity cost to firm  of not changing price tends to be small since
Π
Π
Π

(̄    ) =
+
(̄    )
(̄    )


 
Π
=0+
(̄    )

(19.26)
The first term on the right-hand side of (22.34) vanishes at the profit maxiΠ
mum because 
(̄    ) = 0 i.e., the profit curve is flat at the profit
maximizing price ̄  Moreover, since our thought experiment is one where
 and  remain unchanged, there is no indirect effect of the rise in  via
 or  . Thus, only the direct effect through the fourth argument of the
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19.3. Price setting and menu costs
727
i ( Pi , P,W , M ') i ( Pi , P,W , M ) Pi Pi ' Pi Figure 19.4: The profit curve is flat at the top (  1  and  are fixed,  shifts
to  0   )
profit function is left. And this effect is the same whether or not the price is
changed.
The result reflects a general principle, called the envelope theorem: in
an interior optimum, the total derivative of a maximized function w.r.t. a
parameter equals the partial derivative w.r.t. that parameter.12 The relevant
parameter here is the aggregate money supply, . Hence, the effect of
a change in  on the profit is approximately the same (to a first order)
whether or not the firm adjusts its price. Indeed, owing to the envelope
theorem, for an infinitesimal change in , the profit of firm  is not affected
by a marginal change the price in response to the change in 
For finite changes in  this is so only approximately. Indeed, given a
finite change,  0 − = ∆, the opportunity cost of not changing price can,
by taking a second-order Taylor approximation, be shown to be of “second
order”, i.e., proportional to (∆)2 .13 This is a very small number, when
|∆| is small. Therefore, in view of the menu cost, say  it may be
advantageous not to change price. Indeed, the net gain (=  − opportunity
cost) by not changing price may be positive. Each individual firm is in
the same situation as long as the other firms have not changed price. The
outcome that no firm changes its price is thus an equilibrium. Since there is
11
As by assumption there are no other non-human assets than base money, changes in
the money supply can not be brought about through open market operations.
12
See Appendix A.
13
See Appendix B.
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
no change in the general price level in this equilibrium, a higher output level
results.
What about the labor market?
The considerations above presuppose that workers or workers’ unions do not
immediately increase their wage demands in response to the increased demand for labor. This assumption can be rationalized in two different ways.
One way is to assume that also the labor market is characterized by monopolistic competition between craft unions, each of which supplies its specific
type of labor. If there are menu costs associated with changing the wage
claim and they are not too small, the same envelope theorem logic as above
applies and so, theoretically, an increase in labor demand need not in the
short run have any effect on the wage claims.
There is an alternative way of rationalizing absence of an immediate upward wage pressure. This alternative way is more apt since we have treated
labor as homogeneous, implying that there is no basis for existence of many
different craft unions.14 Instead we will simply assume that there is involuntary unemployment in the labor market. This means that there are people
around without a job although they are as qualified as the employed workers
and are ready and willing to take a job at the going wage or even a somewhat
lower wage. Such a situation is in fact what several labor market theories
tell us we should expect often to be present. Both efficiency wage theory,
insider-outsider theory, collective bargaining theory, and search theory imply
that wages tend to be above the individual reservation wage (see Chapter
23). The resulting presence of involuntary unemployment implies that employment can change with negligible effect on the wage level in the short
run.
19.3.3
Menu costs in action
So even small menu costs can be enough to prevent firms from changing their
price in response to a change in demand. This also implies that even small
menu costs can have sizeable effects on aggregate output, employment, and
social welfare. To understand this latter point, note that under monopolistic
competition neither output, employment or social welfare are maximized in
the initial equilibrium. Therefore the envelope theorem does not apply to
these variables.
14
Even with heterogenous labor, the craft union explanation runs into an empirical
problem in the form of a “too low” wage elasticity of labor supply according to the microeconometric evidence. We come back to this issue in Chapter 22 and 23.
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19.3. Price setting and menu costs
729
This line of reasoning is illustrated in Fig. 19.5. There are two differences compared with Fig. 19.3. First, the specification (19.24) of aggregate
demand is now introduced. Second, along the vertical axis we have set off
the relative price,   so that marginal revenue, MR as well as marginal costs, MC are indicated in real terms, i.e., MR =  and MC
=  For fixed  the demand curve faced by firm  is shown as the
solid downward-sloping curve (  ( )) to which corresponds the
real marginal revenue curve, MR For fixed  the real marginal costs
faced by the firm are shown as the upward-sloping real marginal cost curve,
MC (recall that we consider the case   1)
If firms have rational (model consistent) expectations and know  and
 in advance, we have   = ( ) The price chosen by firm  in advance,
given this expectation, is then the price ̄ shown in Fig. 19.3. As the chosen
price will be the same for all firms, the relative price,   equals 1 for all
 The equilibrium output level for every firm will then be ( ) as
indicated in the figure. If the actual money supply turned out to be higher
than expected, say  0 =    1 and there were no price and wage
adjustment costs and if wages were also multiplied by the factor , prices
would be multiplied by the same factor and real money supply, production,
and employment be unchanged.
With menu costs, however, it is possible that prices and wages do not
change. The menu cost may make it advantageous for each single firm not to
change price. Then, the higher nominal money supply translates into higher
real money supply and the demand curve is shifted to the right, as indicated
by the stippled demand curve in Fig. 19.5. As long as ̄   MC still holds,
each firm is willing to deliver the extra output corresponding to the higher
demand. The extra profit obtainable this way is marked as the hatched area
in Fig. 19.5. Firms in the other production lines are in the same situation
and also willing to raise output. As a result, aggregate employment is on the
point of increasing. The only thing that could hold back a higher employment
is a concomitant rise in  in response to the higher demand for labor. But
the presence of involuntary unemployment in the labor market hinders this.
So the tendency to higher employment is realized and firm ’s production
ends up at 0 in Fig. 19.5, while the price ̄ is maintained. The other
firms act similarly and the final outcome is higher aggregate consumption
and higher welfare.
Thus, the effects on aggregate output, employment, and social welfare
of not changing price can be substantial; they are of “first order”, namely
proportional to |∆| 
In the real world, nominal aggregate demand (here proportional to money
supply) fluctuates up and down around some expected level. Sometimes the
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
Pi
W , M , M ', and P given
P
W 1
P

1
1
yi 
1

 Pi M ' 
,

 P P 
D
 Pi M 
,

 P P 
D

MC
MR
0
M
m P
yi '
yi
Figure 19.5: The impact in general equilibrium of a shift to  0   when menu
costs are binding (the case   1)
welfare effects of menu costs will be positive, sometimes negative. Hence, on
average the welfare effects would appear to cancel out to a first order. This
does not affect the basic point of the menu cost theory, however, which is
that changes in money supply can have first-order real effects (in the same
direction) because the opportunity costs by not adjusting prices are only of
second order.
A reservation As presented here, the menu-cost story is not entirely convincing. The rather static nature of the whole setup is a drawback. A first
weakness is that the setup does not give a clear answer to the question: To
what extent is it a change from a given past price, ̄−1  to the preset price,
̄  for the current period that is costly and to what extent is it a change
from the preset price, ̄  for the current period to another ex-post price
for this period that is costly? Besides, considering a sequence of periods featuring some price stickiness, there would in any period be some prices that
are not at their ex ante “ideal” level. The firms in question are then not
at the flat part of their profit curve. The menu cost necessary to prevent
price adjustment will then be higher for these firms, thus making it more
demanding for menu costs to be decisive.
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19.3. Price setting and menu costs
731
Moreover, in an intertemporal perspective it is present values of the expected stream of future gains and costs that matter rather than instantaneous
gains and costs. An aspect of a complete dynamic modeling is also that ongoing inflation would have to be taken into account. It is well-known that
in modern times where money is paper money (or electronic money), there
is usually an underlying upward trend in the general input price level. To
maintain profitability, the individual producers will therefore surely have to
adjust their prices from time to time. The decision about when and how
much to change price will be made with a view to maximizing the present
value of the expected future cash flow taking the expected menu costs into
account. This is a different situation compared with the purely static profit
maximization in the above analysis.15
The rule of the minimum
For a given price, ̄  it is beneficial for the firm to satisfy demand as long
as the corresponding output level is within the area where nominal marginal
cost is below the price. Returning to Fig. 19.3, let the demand faced by
firm  be denoted  , that is,  = (̄    ) Compare this demand to  ,
defined as the production level at which  = ̄ (assuming   1) This
is the production level known as the Walrasian or classical or competitive
supply of firm  (the superscript “” stands for “classical” or “competitive”).
It is the output that would prevail under perfect competition, given  and
 = ̄  As this output level is a function of only  and ̄  we write 
=   ( ̄ )
So, as long as     we get  =   If demand exceeds   however,
the firm will stick to producing  in that producing beyond this level would
entail a loss (marginal cost above price).
The general rule is therefore that given the predetermined price  = ̄ ,
production becomes
∙
¸
̄  
 = min (   )  ( ̄ ) 
(19.27)

saying that production is determined as the minimum of demand and the
classical supply at the given price. This rule is known as the rule of the minimum. According to this rule, under “normal circumstances” the production
will be determined by the demand since the demand will be the most narrow
limit when actual aggregate demand is not greatly above the expected level.
When the market for good  is in the “normal” state where  −  ( ̄ ) 
0 it is natural to say that this market is a “buyers’ market”. It is, however,
15
As to contributions within this dynamic perspective, see Literature notes.
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
not natural to categorize the state as one of “excess supply”. The difference
 −   ( ̄ ) is completely voluntary on the part of the price-setting firm 
The output level given by the rule of the minimum represents the effective
output supply by firm . The corresponding effective labor demand by firm 
1
is given as  =  from the production function. While postponing details
about the labor market to Chapter 22 and 23, we have above presumed that
involuntary unemployment is present. This means both that offered jobs can
be filled and that unemployed people are still around. If at the same time in
most of the goods markets, the binding constraint in (30.1) is the demand,
then Keynesian unemployment is said to prevail. If instead in most of the
goods markets, the binding constraint in (30.1) is the classical supply, then
classical unemployment is said to prevail. This type of unemployment corresponds to the way non-Keynesian writers in the interwar period interpreted
the existence of huge unemployment as a temporary phenomenon caused by
a “too high real wage”. It is in this context that the quote by Edmond
Malinvaud at the head of this chapter should be seen.
In the World’s Smallest Macroeconomic Model of Section 19.2 classical
unemployment can not occur because of constant marginal costs combined
with a positive mark-up. Similarly, if  = 1 in the present model we have
 =  a constant. Then classical unemployment is impossible here as
well. Indeed ̄ = (1 + )   Hence   ( ̄ ) = ∞ and so (30.1) gives
 = (̄    )    ( ̄ ) automatically for all  (since  is assumed
the same for all ). All the goods markets are demand-constrained and any
unemployment is thereby Keynesian. Note also that because of constant 
combined with the constant mark-up, no menu costs are needed to maintain
that only output not prices respond to changes in aggregate demand,   
19.3.4
Abundant capacity
One of the stylized facts listed in Section 19.1 was that under “normal circumstances” a majority of firms in an industrialized economy respond to shortrun shifts in aggregate demand by adjusting production rather than price.
Key elements of an explanation of this phenomenon have been sketched:
(a) the distinction between Walrasian demand and effective demand; (b)
price setting agents in markets with imperfect competition; (c) the “secondorder argument” that the potential benefit of adjusting the price can easily
be smaller than the cost of adjusting; and (d) because prices are generally
above marginal costs, firms are disposed to rapid quantity adjustment when
aggregate demand shocks occur.
The next problem is whether rapid quantity adjustment is in the main
realizable. Under the assumption that involuntary unemployment is present,
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19.3. Price setting and menu costs
733
lack of workers will not be an impediment. But the production capacity of
firms depends on their capital equipment. To throw light on this aspect we
now let the production function have two inputs, capital and labor.
Putty-clay technology
Suppose firm  has the production function
 = (   )
(19.28)
where  is the installed capital stock and  the labor input,  = 1 2     16
Because of strictly convex installation costs,  is given in the short run. As
raw materials and energy are ignored, in the short run it is only  that can
be varied. So in the short run the capital costs are fixed but labor costs
variable.
Realistic short-run analysis also makes a distinction between the “ex ante”
and the “ex post” production function. By “ex ante” is meant the point in
time where the decision about investment in plant and equipment is to be
made. We may imagine that this decision is made on the basis of the ex ante
production function,  in (19.28). The decision will be made with a forwardlooking perspective. Construction and installation are time consuming and
to some extent irreversible.
By “ex post” is meant “when construction and installation are finished
and the capital ready for use”. In this situation, the substitutability between
capital and labor tends to be limited. Our long-run models in previous chapters implicitly ignored this aspect by assuming that substitutability between
capital and labor is the same ex ante and ex post. In reality, however, when
a machine has been designed and installed, its functioning will often require
a more or less fixed number of machine operators. What can be varied is just
the degree of utilization of the machine per time unit. In the terminology of
Section 2.5, technologies tend in a short-run perspective to be “putty-clay”
rather than “putty-putty”.
An example: Suppose the production function,  in (19.28), is a neoclassical production function. This could then be the ex ante production
function. Ex post, however, this function no longer describes the choice
opportunities for firm . These are instead given by a Leontief production
function with CRS:
 = min( ̄   )
  0   0
16
(19.29)
Note that, contrary to earlier chapters,  is here not the capital-labor ratio, but
simply the capital stock in firm 
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
where  and  are given technical coefficients, ̄ is the size of the installed
capital (now a fixed factor), and  is its utilization rate (0 ≤  ≤ 1)  =
1     17 Presumably the firms would have acquired their capital equipment
under different circumstances at different points in time in the past so that,
generally, the equipment would be somewhat heterogeneous and  and 
would be index numbers and differ across the firms. But to make aggregation
simple, the analyst may be tempted in a first approach to ignore this and
assume  and  are the same across the firms.
Capacity utilization in a Keynesian equilibrium
Under “full capacity utilization” we have  = 1 (each machine operating “full
time” seven days a week, allowing for surplus time for repairs and maintenance); “capacity” is given as ̄ per week. Producing efficiently at capacity
requires  = ̄  But if demand,   is less than capacity, satisfying this
demand efficiently requires  =  (̄ )  1 and  =   As long as
  1 there is unused capacity and marginal productivity of labor in firm 
is a constant, 
The (pure) profit of firm  is Π =   − C(    ) where C( ) =
   + is the cost function with  denoting the fixed costs deriving from
the fixed production factor, ̄ . Average cost is  = C( ) = + 
and marginal cost is a constant  =  for   ̄ 
Fig. 19.6 depicts these cost curves together with a downward-sloping
demand curve. A monopolistic-competition market structure as described
in Section 19.3.1 is assumed but now only a subset of the  firms produce
differentiated consumption goods. The other firms produce differentiated
capital goods, also under conditions of monopolistic competition and with
the same price elasticity of demand.
Firm  presets the price of good  at  = ̄ in the expectation that
the level of demand will be as indicated by the downward sloping D curve
in Fig. 19.6. The point  in the figure represents a standard shortrun equilibrium under monopolistic competition with output level such that
 =  Assuming full symmetry across the different firms, the point
 would also reflect a Keynesian equilibrium if the actual demand level
(position of the demand curve) had turned out to be as expected by the firms
when fixing their price. But in the figure it is assumed that the demand level
turned out lower. The produced quantity is reduced while the price remains
unchanged (because of either menu costs or simply the constant marginal
costs combined with constant price elasticity of demand). Firm  ends up
17
The link between the ex ante production function  and the technical coefficients 
and  was described in Chapter 2.
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19.3. Price setting and menu costs
735
Pi
AC
MC
Pi

MC
ESR
D
D'

MR
y´i
Aki
yi
Figure 19.6: Firm  in a Keynesian equilibrium (̄ is production capacity; MC
curve first horizontal and then vertical at  = ̄ ).
with actual production equal to 0 in Fig. 19.6. The obtained profit is
indicated by the hatched rectangle constructed by the help of the average
cost curve .
If instead the actual demand level had turned up higher than expected,
firm  would be induced to raise production. There is scope for this because
price is above marginal costs the whole way up to full capacity utilization.
Profits will in this manner become substantially higher than expected because
the AC curve is downward-sloping up to ̄ .
Such a situation where the quantity produced is less than the quantity
at which average costs are at the minimum, here at ̄ , is in the theory of
industrial organization said to reflect “excess capacity”. As “excess” sounds
as if the situation reveals a kind of inefficiency, which in fact need not be the
case, we prefer the term “abundant capacity”.
A monopolistic-competition long-run equilibrium
The picture is essentially the same in a “free-entry-and-exit equilibrium”
where all pure profit is eliminated; in the theory of industrial organization
this is traditionally called a “long-run equilibrium”. Suppose that initially
some of the firms obtain positive pure profits as illustrated in Fig. 19.6.
This state of affairs invites entry of new firms. Over time these set up new
plants and begin to supply new differentiated goods from a large set of as
yet unutilized possible imperfect substitutes for the existing goods. The
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
entry process continues until equilibrium with zero pure profits obtains in all
product lines. When this state is reached, prices equal both short-run and
long-run average costs, and each firm operates where the downward-sloping
demand curve is tangent to both AC curves. We here use the terms “shortrun” and “long-run” as they are used in the theory of industrial organization.
That is, “short run” refers to a time horizon where only a subset of the
production factors are variable, while “long run” refers to a long-enough
time horizon for all production factors to be variable.
From a macroeconomic perspective the important conclusion is that the
“transition” from short-run equilibrium to long-run equilibrium in no way
tends to lessen the presence of abundant capacity in the firms.
To portray a long-run equilibrium, we only need to let the AC curve
for firm ’s chosen plant and equipment be tangent to the demand curve
at the point  . This is what we have done in Fig. 19.7 where also the
long-run marginal and average cost curves are visible, denoted LMC and
LAC, respectively. The LMC curve is assumed U-shaped. This implies a
U-shaped LAC curve. The downward-sloping part of the LMC curve may
be due to indivisibilities of plant and equipment and the upward-sloping part
as reflecting coordination problems or an implicit production factor which is
tacitly held fixed (a special managerial expertise, say).
In Fig. 19.7 we have moreover assumed that the short-run marginal
cost curve,  is horizontal only up to certain output level. It then rises
gradually to end up as vertical at full capacity utilization. This may reflect
that less efficient standby equipment is being brought to use, and the wear
and tear on the machinery is gradually increased. This amounts to a plausible
rounding off of the probably too “sharp” Leontief production (19.29). In
relation to the production function in Section 19.3.1, this roughly corresponds
to assuming that for production up to a certain level,  in (19.20) equals 1
whereas beyond this level  is less than 1. An additional reason for the MC
curve to be upward-sloping at high capacity utilization is wage bonuses for
working on the night shift or in the weekend.
Also in this more realistic setup is abundant capacity revealed as a sustainable equilibrium phenomenon. In long-run equilibrium each firm produces
at a point where:
• price is above marginal costs so as to exactly cover fixed costs;
• the quantity produced is less than the quantity at which average costs
are at the minimum (i.e., where the MC curve crosses the AC curve in
Fig. 19.7), given the firm’s preferred plant and equipment.
The conclusion is that as long as the AC curve does not shift (this would
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19.3. Price setting and menu costs
737
Pi
AC
MC
LMC
ESR

Pi
MC

D
MR
yi
*
LAC
A*k i*
yi
Figure 19.7: Firm  in a monopolistic-competition long-run equilibrium (∗ is longrun equilibrium output and ∗ ∗ is long-run production capacity).
happen if the wage level changed), firms are more than willing to accommodate an increased demand (outward shift of the demand curve) at an
unchanged price or even at a lower price by an increase in production. Similarly, an inward shift of the demand curve will not induce a temptation to
reduce the price, rather the opposite if the menu cost is immaterial. These
observations fit well with the empirical evidence that measured total factor
productivity and profits rise in an economic upturn and fall in a downturn,
an issue to which we return in Part VII of this book.
In the real world some markets are better characterized by strategic interaction between a few big firms than by monopolistic competition. But
also such firms may have an incentive to maintain abundant capacity. This
will make credible a threat to cut price in response to unwelcome entry by a
competitor.
The role of indivisibilities
The downward-sloping part of the LAC curve, reflecting indivisibilities in
plant and equipment, is important also from another perspective. Without
indivisibilities it may be difficult to see why involuntarily unemployed workers
could not just employ and support themselves in the backyard, financing the
needed tiny bits of capital by tiny bank loans.
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19.4
CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
The IS-LM model
After these reflections about the context of short-run analysis, we are ready to
present the IS-LM model. The key new element compared with the World’s
Smallest Macroeconomic Model is that an interest-bearing asset is added.
The version of the IS-LM model presented here is in many respects similar
to the familiar one known from introductory and intermediate textbooks. It
is essentially static and deals with mechanisms that are likely to be operative
within a single period of length a quarter of a year, say, or at least not more
than one year. The focus is on the interaction between the output market
and the asset markets. The model conveys the central message of Keynes’
theory: the equilibrating role in the output and money markets is taken by
output and nominal interest rate changes.
19.4.1
The building blocks
We consider a closed economy with a private sector, a government, and a
central bank. The produce of the economy consists mainly of manufacturing
goods and services, supplied under conditions of imperfect competition and
price stickiness of some sort. “Money supply” means money in the broad
sense and thus includes bank created money in addition to currency in circulation.
The model starts out directly from presumed aggregate behavioral relationships that are supposed to roughly characterize aggregate behavioral
responses to changes in exogenous variables, at least under “normal circumstances”. The aim is to deliver qualitatively valid rather than quantitatively
precise answers to questions about the functioning of the economy in the
short run.
The output market
Demand Aggregate output demand is given as


  = (   +1
   ) + (+1
   ) +  +  
(19.30)
  0    0   +   +    1 ()  0  ≤ 0
   0 +1
+1
+1
+1
  0   0
where the function (·) represents private consumption, the function (·)
represents private fixed capital investment,  is public spending on goods and
services, and  is a shift parameter (possibly stochastic) summarizing the
role of unspecified exogenous variables that may matter for aggregate output
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19.4. The IS-LM model
739
demand. One of these variables could be the general “state of confidence”
and another the preference for the present relative to the future. Arguments
appearing in the consumption and investment functions include   which is

current private disposable income, +1
which is expected output the next
period (or periods),  and  which are commented on below, and finally 
which is the expected short-term real interest rate. In this first version of
the model we assume there is only one short-term real interest rate in the
economy.
The signs of the partial derivatives of the consumption and investment
functions in (19.30) are explained as follows. A general tenet from earlier
chapters is that consumption depends positively on household wealth. One
component of household wealth is financial wealth, here represented by the
market value,  ·  of the capital stock  (including the housing stock).
Another component is perceived human wealth (the present value of the
expected labor earnings stream), which tends to be positively related to

both   and +1
. The separate role of disposable income,    reflects the
hypothesis that a substantial fraction of households are credit constrained.
The role of the interest rate,  reflects the hypothesis that the negative
substitution and wealth effects on current consumption of a rise in the real
interest rate dominate the positive income effect.

Firms’ investment depends positively on +1
. This is because the productive capacity needed next period depends on the expected level of demand
next period. In addition, investment in new technologies is more paying when
expected sales are high. On the other hand, the more capital firms already
have, the less they need to invest, hence   0. Finally, the cost of investing
is higher the higher is the real interest rate. These features are consistent
with the -theory of investment when considering an economy where firms’
production is demand constrained.
Disposable income is given by
  ≡  − T
(19.31)
where  is aggregate factor income (= GDP) and T is real net tax revenue
(equal to gross tax revenue minus transfers). We assume a quasi-linear net
tax revenue function
T =  +  ( )
0 ≤  0  1
(19.32)
where  is a constant parameter reflecting “tightness” of discretionary fiscal
policy. Fiscal policy is thus described by two variables,  representing government spending on goods and services and  representing the discretionary
element in taxation. A balanced primary budget is the special case  +  ( )
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
=  The endogenous part,  ( ) of the tax revenue is determined by the
given taxation rules; when  0  0 these rules act as “automatic stabilizers”
by softening the effects on disposable income, and thereby on consumption,
of changes in output and employment.

With regard to expected output next period, +1
 the model takes a

shortcut and assumes +1 is simply an increasing function of current output
and nothing else:

+1
= ( )
0  0 ≤ 1
(19.33)
We may write aggregate private output demand in a more compact way.
First, since we only consider a single period, we can treat the amount of
installed capital as a given constant, ̄ Hence, for convenience we suppress
the explicit reference to ̄ and ̄ in the consumption and investment func˜
tions, respectively, and write these functions as ̃(·) and (·)
respectively.
Second, inserting (19.31) and 19.33) into (19.30), we can then express aggregate private demand as a function (    ) ≡ ̃( −  −  ( ) ( )  )
˜
+((
)  ) So total output demand is
  = (    ) +  +  
where
0
0
 +   ) ( )  1
0   =   (1 −  ) + (+1
+1
 =  +   0 and  =   · (−1) ∈ (−1 0)
(19.34)
(19.35)
Production and employment Prices on goods and services have been set
in advance by firms operating in markets with monopolistic competition. In
response to shifts in demand, owing to either constant marginal costs or the
presence of menu costs, firms change production rather than price. There
is scope for maintaining profitability this way because prices are normally
above marginal costs.
Behind the scene there is an aggregate production function,  =  (̄ )
where  is the level of employment. The conception is that under “normal
circumstances” there is abundant capacity. That is, ̄ is large enough so
that for some   ̄, where ̄ is the labor force, output demand can be
satisfied, i.e.,
 (̄ ) =   
(19.36)
without violating the rule of the minimum as defined in Section 19.3. Assuming   0 we can solve the equation (19.36) for the desired employment, 
and write  = N (   ) where N   0 and N  0 under the assumption
that   0.
The desired employment can and will be realized provided it is smaller
than ̄ − ̃ where ̃ is the sum of frictional unemployment (which is inevitable when workers change jobs and location in a vibrant economy) and
c Groth, Lecture notes in macroeconomics, (mimeo) 2013.
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19.4. The IS-LM model
741
voluntary unemployment (unemployed people with reservation wage above
the going wage). The remainder of the labor force is ready for work here and
now at the going wage. The IS-LM model assumes this group is normally
large enough to allow realization of  = N (   ). The remaining part of
the labor force is called ̂ and consists of those who are involuntarily unemployed (i.e., those who are ready and willing to work at the going wage or
even a somewhat lower wage).
With  denoting total unemployment, the labor force is hereby decomposed this way:
̄ ≡  +  ≡  + ̃ + ̂
In an alternative decomposition of unemployment one writes
 =   +  
where   is the natural unemployment level and   the remainder unemployment, often called the cyclical unemployment level (a positive number in
a recession, a negative number in a boom). So   is defined as the level of
unemployment that prevails when the unemployment rate, ̄ equals the
natural (or structural) rate of unemployment. This is defined as that rate
of unemployment which generates neither upward nor downward pressure on
the inflation rate. An alternative name for this is the NAIRU.18 The term
“natural” has become standard although it is a misnomer since there is nothing natural about that unemployment rate. Besides, identifying absence of
pressure on the inflation rate with a particular rate of unemployment may
be problematic. There are empirics as well as theories around saying that
there tends to be a range of unemployment rates within which no pressure
on the inflation rate is generated, neither upward nor downward.19
Many textbooks ignore this rate-versus-range issue and speak of the natural level of output as a unique level of output,    realized when the unemployment is at the supposed unique natural rate:
  =  (̄   )
where   ≡ ̄ −  is denoted the natural level of employment. Until further
notice, we stick to this convenient terminology − with the proviso mentioned.
Some authors use the term full-employment output as synonymous with   
others are reluctant to do that. In any case,   and   are affected by legal
institutions and economic policy
18
Non-Accelerating-Inflation-Rate-of-Unemployment.
At least at low levels of inflation this should be so, cf. Akerlof et al. (2000) and
Hendry and ? (2013). In Chapter 23 we go into detail with the labor market.
19
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
While the size and composition of unemployment matter for wage and
price inflation, the IS-LM model considers such effects as not materializing
until at the earliest the next period. Being concerned about only a single
short period, the model is therefore usually tacit about production and employment aspects and leave them “behind the scene”.
Asset markets
In this first version of the IS-LM model we assume that only two financial
assets exist, money and an interest-bearing short-term bond. The latter may
be issued by private agents and the government. Although not directly visible
in the model, there are commercial banks that accept deposits and provide
bank loans to households and firms. Bank deposits are assumed to earn no
interest at all but they are attractive because they in general provide a fairly
secure store of liquidity due to government-guaranteed deposit insurance.20
The bank lending rate allows the banks a revenue to cover the costs associated
with banking.
Let  denote the money supply in a broad sense. That is, in addition to
currency in circulation, the bank-created money in the form of liquid deposits
in the banks is included in  We may thereby think of  as close to what
is in the statistics denoted 1 or 2 , cf. Chapter 16. The bank lending
rate equals the short-term nominal interest rate,  on government bonds.
All interest-bearing assets are considered perfect substitutes from the point
of view of the investor and will from now just be called “bonds”.
The demand for money is assumed given by
  =  · (( ) +  )
  0   0
(19.37)
where  is the output price level (the GDP deflator) and  is a shift parameter (possibly stochastic) summarizing the role of unspecified exogenous
variables that may matter for real money demand. Apart from the shift
term,   real money demand is given by the function ( ) which is called
the liquidity preference function. The first partial derivative of this function
is positive reflecting the transaction motive for holding money. The output
level is an approximate statistic (a “proxy”) for the flow of transactions for
which money is needed. The negative sign of the second partial derivative
reflects that the interest rate,  is the opportunity cost of holding money
instead of interest-bearing assets.
The part of non-human wealth not held in the form of money is held in
the form of an interest-bearing one-period bond. This bond yields a payoff
20
In practice even checkable deposits in banks usually earn a small nominal interest, but
this is ignored by the model.
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19.4. The IS-LM model
743
equal to 1 unit of account at the end of the period. Let the market price of
the bond at the beginning of the period be  units of money. The implicit
nominal interest rate,  is then determined by the equation (1 + ) = 121
i.e.,
 = (1 − )
(19.38)
There is a definitional link between the nominal interest rate and the expected short-term real interest rate,  . In continuous time we would have
 =  −   with  as the instantaneous nominal interest rate (with continuous compounding) and  (≡ ̇  ) as the (forward-looking) instantaneous
inflation rate, the superscript  indicating expected value.
In discrete time the appropriate way of defining  is more involved. The
holding of money is motivated by the need, or at least convenience, of ready
liquidity to carry out expected as well as unexpected spending in the near
future. To perform this role, money must be held in advance, that is, at
the beginning of the (short) period in which the purchases are to be made
(“cash in advance”). If the price of a good is  euro to be paid at the end
of the period and you have to hold this money already from the beginning
of the period, you effectively pay  +  for the good, namely the purchase
price,  plus the opportunity cost,  Postponing the purchase one period
thus gives a saving equal to  +  . The price of the good next period is
+1 which, with cash in advance, must be held already from the beginning
of that period. So the real gross rate of return obtained by postponing the
purchase one period is
1+
1
=

1 +  = (1 + )
+1
1 +  +1
where  +1 ≡ (+1 −  ) is the inflation rate from the current to the next
period. As seen from the current period, +1 and  +1 are generally not
known. So decisions are based on the expected real interest rate,
1+
− 1 ≈  −  +1 
(19.39)
 =
1 + +1
where the approximation is valid for “small”  and +1 
19.4.2
Keynesian equilibrium
The model assumes clearing in both the output and the money market:



21
= (  −  +1   ) +  +  
= ( ) +  
In continuous time with compound interest,  = 1 so that  = − ln 
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(IS)
(LM)
744
CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
where, for simplicity, we have used the approximation in (19.39), and where
 is the available money stock at the beginning of the period. In reality
the central bank has direct control only over the monetary base. Yet the
traditional understanding of the model is that through this, the central bank
has under “normal circumstances” control also over  With  given by
monetary policy, the interpretation of the equations (IS) and (LM) is therefore that output and the nominal interest rate quickly adjust so as to clear
the output and money markets.
The equation (IS), often named the IS equation, asserts clearing in a flow
market: so much output per time unit matches the demand per time unit for
this output. The name comes from an alternative way of writing it, namely
as  =  (investment = saving, where saving =  −  −  −  )
In contrast, the equation (LM), often called the LM equation, asserts
clearing in a stock market: so much liquidity demand matches the available
money stock,  at a given point in time, here the start of the period. At
the theoretical level the period length is thus understood to be very short.
At the empirical level we have data for  and  on a daily basis, whereas the
period length of data for aggregate output, consumption, and investment, is
usually a year or at best a quarter of a year. So in econometric analyses,
instead of letting the model’s  and  refer to a point in time, the average
money stock and interest rate over a year or a quarter of a year may be used.
Having specified the LM equation, should we not also specify a condition
for clearing in the market for bonds? The answer is that we do not have to.
The balance sheet constraint guarantees that clearing in the money market
implies clearing in the bond market − and vice versa. To see this, let 
denote the nominal financial wealth of the non-bank public and let  denote
the number of one-period bonds held net by the non-bank public. Then
 +  ≡  With  denoting the demanded quantity of bonds, we have
  +  =  This is called the balance sheet constraint and implies a kind
of “Walras’ law for stocks”. Subtracting the first from the second of these
two equations yields
(19.40)
  −  + ( − ) = 0
Given   0 it follows that if and only if   =  then  =  That
is, clearing in one of the asset markets implies clearing in the other. Hence
it suffices to consider just one of these two markets explicitly. Usually the
money market is considered.
The IS and LM equations constitute the traditional IS-LM model. The
exogenous variables are   +1         and, in the traditional interpretation, . Given the values of these variables, a solution, ( ) to the
equation system consisting of (IS) and (LM) is an example of a Keynesian
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19.5. Alternative monetary policy regimes
745
equilibrium.
The current price level,  is seen as predetermined and maintained
through the period, but the price level +1 set for the next period will presumably not be independent of current events. So expected inflation,  +1 
ought to be endogenous. It is therefore a deficiency of the model that  +1
is treated as exogenous. Yet this may give an acceptable approximation as
long as the sensitivity of expected inflation to current events is small.
19.5
Alternative monetary policy regimes
We shall analyze the functioning of the described economy in three alternative
monetary policy regimes. We first consider the traditional case where the
central bank is assumed to maintain the money supply at a given target
level. Next we consider the case where the central bank, trough open market
operations, maintains  at a certain target level. The third monetary policy
regime to be considered is a counter-cyclical interest rate rule where both 
and  are endogenous.
19.5.1
Money stock as target
Here the central bank maintains the money supply at a certain target level,
 In addition to the output level, the interest rate is endogenous. The determination of the endogenous variables,  and  is conveniently illustrated
by an IS-LM diagram. Until further notice it is assumed that circumstances
are such that the solutions for  and  are strictly positive.
Consider the IS-LM diagram in Fig. 19.8. The IS curve is the locus of
combinations of  and  that are consistent with clearing in the output market, i.e., consistent with the IS equation. Since   0 (·) is a monotonic
function of  Consequently, (IS) gives  as an implicit function of   +1    
and  :
 =  (  +1      )
The partial derivatives of this function can be found by taking the differential
on both sides of (IS):
 =   +  ( − +1 ) +   +  +  
(19.41)
We find | by setting  +1 =  =  =  = 0 and reordering:


=
|
1 − 
 0

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(19.42)
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
where the sign comes from (19.35). That is, higher aggregate demand in
equilibrium requires that the interest rate is lower.
Similarly, the LM curve is the locus of combinations of  and  that are
consistent with clearing in the money market, i.e., consistent with the equation (LM). The liquidity preference function, (·) is a monotonic function
of  since   0. Therefore, (LM) gives  as an implicit function of  
and  :

 =  (   )

The partial derivatives can be found by taking the differential on both sides
of (LM):

( ) =   +   +  
(19.43)

We find | by setting ( ) =  = 0 and reordering:


=
|
−
 0

(19.44)
That is, for real money demand to equal real money supply, a higher volume
of transactions must go hand in hand with a higher interest rate.
Fig. 19.8 shows the downward sloping IS curve and the upward sloping
LM curve. A solution ( ) to the model is unique and we can write  and
 as implicit functions of all the exogenous variables:
 
         )
 +1

 = (   +1        )


= (
(19.45)
(19.46)
Comparative statics
How do  and  depend on the exogenous variables? A qualitative answer
can easily be derived by taking into account in what direction the IS curve
or the LM curve in Fig. 19.8 shifts in response to a change in an exogenous
variable.
A quantitative answer is obtained by finding the partial derivatives of
the implicit functions  (·) and (·) evaluated in the equilibrium point. A
convenient method is based on Cramer’s rule as follows. The two equations, (19.41) and (19.43), constitute a new equation system with two new
endogenous variables, the changes  and  The changes, +1    
  ( ) and   in the exogenous variables are our new exogenous
variables. The coefficients to the endogenous and exogenous variables are
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19.5. Alternative monetary policy regimes
747
i IS
LM G  0 M  0  Yn Y
Figure 19.8: The IS-LM cross when  is exogenous; a case with equilibrium output
below the natural level,   ( +1        and  given).
derivatives evaluated at the equilibrium point. Like the old system the new
system is simultaneous (not recursive). The key point is that the new system is linear. We first reorder (19.41) and (19.43) so that  and  appear
on the left-hand side and the differentials of the exogenous variables on the
right-hand side of each equation:
(1 −  ) −   = −  +1 +   +  +  

  +   =  −  

From this linear system we find  and  by Cramer’s rule:
¯
¯
¯ − +1 +   +  +  − ¯
¯
¯
¯

− 
 ¯

 =
∆
 (−  +1 +   +  +  ) +  ( 
−  )

(19.47)
=
∆
and
¯
¯
¯ 1 −  −  +1 +   +  +  ¯
¯
¯
¯ 
¯

− 

 =
∆

(1 −  )( 
−

)
 −  (−  +1 +   +  +  )


=
∆
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
where the determinant ∆ is defined by
¯
¯
¯ 1 −  − ¯
¯
¯ = (1 −  ) +    0
∆=¯

 ¯
(19.48)
Finally, we get the partial derivatives of (·) and (·) respectively, w.r.t.
the real money supply,  by setting +1 =  =  =  =  = 0
and reordering. Thereby


 0
=  =

(1 −  ) +  
(  )
1 − 

 0
=  =

(1 −  ) +  
(  )
in view of (19.35) and (19.48). Such partial derivatives of the endogenous
variables w.r.t. an exogenous variable, evaluated at the equilibrium point,
are called multipliers. The short-run effect on  of a small increase in 
can be calculated as ∆ ≈ ( ( 
))∆ Thus, the partial derivative

w.r.t.  acts as a multiplier on the increase, ∆ , in the exogenous
variable,  .22
The intuitive interpretation of the signs of these multipliers is the following. The central bank increases the money supply through an open market
purchase of bonds held by the private sector. Immediately after this, the
supply of money is higher than before and the supply of bonds available to
the public is lower. At the initial interest rate there is now excess supply of
money and excess demand for bonds. But the attempt of agents to get rid of
their excess cash in exchange for more bonds can not succeed in the aggregate
because the supplies of bonds and money are given. Instead, what happens
is that the price of bonds goes up, that is, the interest rate goes down, cf.
(19.38), until the available supplies of money and bonds are willingly held by
the agents. Money is therefore not neutral.
The output multiplier w.r.t. government spending on goods and services,
often just called the spending multiplier, is


1
=  =
=



(1 −  ) +  
1 −  +   
22
(19.49)
Instead of using Cramer’s rule, in the present case we could just substitute , as
determined from (19.43), into (19.41) and then find  from this equation. In the next
step, the found solution for  can be inserted into (19.43), which then gives the solution
for  However, if  were a function that could become nil, this procedure might invite
a temptation to rule this out by assumption. That would imply an unnecessary reduction
of the domain of  (·) and (·) The only truly necessary assumption is that ∆ 6= 0 and
that is automatically satisfied in the present problem.
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19.5. Alternative monetary policy regimes
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evaluated at the current equilibrium, ( ) Under the assumed monetary
policy we thus have 0     1(1 −  ) The difference, 1(1 −  )
−  is due to the financial crowding-out effect, represented by the term
    0 in (19.49). Owing to the fixed money supply, the expansionary
effect of a rise in  is partly offset by a rise in the interest rate induced by the
increased money demand resulting from the “initial rise” in economic activity. Without the financial crowding-out effect, the spending multiplier would
be above one. Another “moderator” comes from the marginal net tax rate,
 0 ( ) which by reducing the private sector’s marginal propensity to spend,
  cf. (19.35), acts as an “automatic stabilizer”. When income (economic
activity) rises, disposable income rises less, partly because of higher taxation, partly because of lower aggregate transfers, for example unemployment
compensation.
Shifts in the values of the exogenous variables,  and   should be interpreted as shocks (disturbances) coming from unspecified sources outside
the system. A positive demand shock,   0 may be due to an upward
shift in households’ and firms’ general level of “confidence”. A positive liquidity preference shock may reflect a downward shift in “confidence”, that
is, higher perceived risk associated with bond holdings. On the other hand,
improvements in the payment technology (widespread transition to electronic
home banking, say) may shift both the money multiplier and money velocity,
(  ) upward which in the model would be represented by   0
To see how demand shocks and liquidity preference shocks, respectively,
affect output under the given monetary policy, we first set  +1 =  = 
= 
= 0 in the equation (19.47). Then, setting  = 0 (or  = 0), we

find the partial derivative of  w.r.t.  (or  ) :


1
=  =
=

(1 −  ) +  
1 −  +   

−
=  =
 0

(1 −  ) +  
As expected, a positive demand shock is expansionary, while a positive liquidity preference shock is contractionary because it raises the interest rate.
Note that   =   (from (19.49)) in view of the way  enters the
IS equation.
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
How does higher expected inflation affect   and  ? We find

− 

=

=
 0

+1
 +1
(1 −  ) +  

 
= +1 =
∈ (0 1)
(19.50)

 +1
(1 −  ) +  
( −  +1 )

−(1 −  )
=
= +1 − 1 =
∈ (−1 0)


 +1
 +1
(1 −  ) +  
A higher expected inflation rate thus leads to a less than one-to-one increase
in the nominal interest rate and thereby a smaller expected real interest
rate. Only if money demand were independent of the nominal interest rate
( = 0) as the quantity theory of money claims, would the nominal interest
rate rise one—to-one with  +1 and the expected real interest rate thereby
remain unaffected.
Before proceeding, note that there is a reason that we have set up the IS
and LM equations in a general nonlinear form. We want the model to allow
for the empirically important feature that the different multipliers generally
depend on the “state of the business cycle”. The spending multiplier, for
instance, tends to be larger in a slump than in a boom.
19.5.2
The nominal interest rate as target
Instead of targeting a certain level of the money supply, the central bank
now maintains the nominal interest rate at a certain target level   0
This version of the model corresponds better to how central banks nowadays
operate in practice. The central bank announces a target level of the nominal
interest rate and through open-market operations adjusts the monetary base
until the target rate is realized.
In this setup  is exogenous, while  is endogenous along with  . Instead
of the upward-sloping LM curve we get a horizontal line, the  line (“”
for interest rate) in Fig. 19.9. The model is now recursive. Since  does
not enter the IS equation,  is given by this equation independently of the
LM equation. Indeed, the IS equation determines  as an implicit function
 = ( −  +1      )
(19.51)
Comparative statics
By considering the IS equation in the form (19.41), we shall find the partial
derivatives of the  function. For example, the partial derivatives w.r.t. the
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19.5. Alternative monetary policy regimes
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i IS e , ,G ,D IR Yn Y Figure 19.9: A fixed interest rate implying equilibrium output close to the natural
level (  +1     and  given).
interest rate, public spending, a demand shock, and a liquidity preference
shock, respectively, are


 0
=

1 − 


1
=
=
 1


1 − 

= 0

(19.52)
The latter derivative shows that a liquidity preference shock has no effect on equilibrium output. The shock is immediately counteracted by a
change in the money supply in the same direction, so that the interest rate
remains unchanged. Thus, the liquidity preference shock is “cushioned” by
the monetary policy.
On the other hand, a shock to output demand has a larger effect on output
than in the case of money stock targeting (compare (19.52) to (19.49). This
is because under money stock targeting a dampening rise in the interest rate
was allowed to take place. But with a constant interest rate this financial
crowding-out effect does not occur.
From this kind of analysis, Poole (1970) concluded that:
• a money stock targeting rule is preferable (in the sense of implying less
volatility) if most shocks are output demand shocks, while
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
• an interest rate targeting rule is preferable if most shocks are liquidity
preference shocks.
By inserting the solution for  from (19.51) into (LM), we find the money
supply required to obtain the target interest rate  We get
 =  · (( ) +  ) =  · ((( −  +1      ) ) +  )
Taking the differential on both sides of (LM) yields
 =  (  +   +  ) +



(19.53)
This implies










+  )  0
+  ) =  (

1 − 
1
=  
 0
1 − 
=  (
=   0
=

 0

Since for a fixed interest rate there is no financial crowding-out, the production outcome can also be illustrated by a standard 45◦ “Keynesian cross”
diagram as in Fig. 19.10.
Under a constant interest rate policy the effect on  of a one-unit increase in  is given via the spending multiplier   = 1(1 −  )  1
from (19.52). Since the fiscal tightness parameter  is unchanged, the net tax
revenue only rises according to the rule T =  0 ( ) which under “normal
circumstances” tends to be less than  This is so in spite of the fact that
   in view of the spending multiplier being above one, given a constant interest rate. So it is here understood that the increase in  is financed
by allowing a budget deficit to be larger than otherwise.
This brings the issue of Ricardian equivalence into the picture.
Ricardian non-equivalence The Keynesian grounds for rejecting Ricardian equivalence as an acceptable approximation are sharpest under interest
rate targeting. The skepticism about Robert Barro’s portrait of the household sector as a set of infinitely lived dynasties is one thing. On top of this
comes that refutation of Ricardian equivalence has stronger implications in
an economy where output is determined by aggregate demand.
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19.5. Alternative monetary policy regimes
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Yd D(Y , r,  )  G   D 45 Yn Y Figure 19.10: Given a fixed interest rate, a “Keynesian cross” diagram is sufficient
to display the equilibrium output level ( =  −  +1     and  given).
Consider the question: To what extent, if at all, will a deficit-financed
increase in  result in crowding out of current private consumption? As a
thought experiment, let us temporarily assume that Barro’s portrait of the
household sector is an acceptable approximation. Facing a deficit-financed
increase in , the household dynasties thus set aside savings to fully prepare
for the deficit-induced higher taxes in the future. In an economy with full
capacity utilization and inelastic labor supply private consumption would
fall correspondingly. In an economy with less than full capacity utilization
and involuntary unemployment, however, there is no reason that private consumption should fall. On the contrary, by shifting people from unemployment
to work, the higher  entails both higher production and higher disposable
income. So there is scope for a response involving a rise in private saving
without a reduction in private consumption. And the prediction of the ISLM model is that under the interest rate targeting rule, this is exactly what
will take place. How do we know? Because “the balanced budget multiplier”
is at least 1, as we shall now see.
The balanced budget multiplier
What will be the effect on  of a rise in  if we require an always balanced
budget? Letting the rise in  be financed by a corresponding rise in the tax
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
revenue, T implies
T =  +  0 ( ) = 
There will be an automatic rise in tax revenue via  0 ( )  0, but generally
an exactly balanced budget will require a simultaneous adjustment of the
fiscal tightness parameter,   of size
 =  −  0 ( )
Now,
 =




 +
 =
 +
( −  0 ( ) )




By ordering,
 =


1+



 0


+
From (19.41) with  =  +1 =  =  = 0 we find  =  (1 −
 )  0 Thus, the total effect on  of a unit increase in  under a balanced
budget policy approximately equals the total derivative w.r.t.  which is
1+


+ 

1 + 
=    0 = 1−  0 =

1 −  +   0
1 +  
1 + 1−
1 −  
≥ 1
=
 +   )0 ( )
1 −   − (+1
+1
where we have used (19.35). This is called the balanced budget multiplier. In
 +   = 0 it equals exactly 1. This is the famous Haavelmo result
case +1
+1
(Haavelmo, 1945).
If the interest rate were allowed to increase, as would be the case with a
constant  (the -exogenous regime), then the balanced budget multiplier
would be smaller because of the implied financial crowding-out effect.
Back to the Ricardian equivalence issue Let us now return to the issues of crowding out and Ricardian equivalence raised above. With a constant
interest rate we have under a balanced budget that  ≥  = T  0 in
view of the balanced budget multiplier being at least 1. Thereby, the change
in disposable income is  −T ≥ 0. With infinitely lived Barro-style dynasties the situation is the same if the government instead of a balanced budget
policy allows government debt temporarily to rise, thereby postponing the
extra taxation. Then from the raised current disposable income the households just set aside extra savings in the same amount. So in both cases,
with a constant interest rate the increased  generates a rise in output at
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19.5. Alternative monetary policy regimes
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least as high as the increase in  and, a fortiori, not less than the increase
in T This amounts to a nonnegative change in current after-tax income,
 − T and thereby private consumption,  tends to rise, if anything. So
there is no crowding out of private consumption, but possibly crowding in.
As  is raised and monetary policy keeps the interest rate unchanged, also
investment tends to be “crowded in” rather than “crowded out”.
We conclude that introducing Barro-style dynasties in a Keynesian framework will not take away the expansionary effect of the increase in  It will
only make it smaller than otherwise. The spending multiplier is at least
one in a situation with unemployment and abundant capacity. The quantitative importance of Ricardian non-equivalence is enhanced compared with
a situation with full employment and full capacity utilization as in classical
theory. There is the usual effect that taxing less now and more later increases
aggregate private consumption now, because the current tax cut raises aftertax income of current tax payers who are aware that the set of future tax
payers will partly include new people. In addition, current private beforetax income is raised because the rise in private consumption is not offset by
lower investment, but tends to raise aggregate demand and production in the
economy.
The paradox of thrift
An instructive special case of (19.30) is:
  =  +  +  + 
˜ −  +1 ) +  +   with
= 0 + 1 ( − T) − 2 ( −  +1 ) + (
T =  +  1  where 0  0 0  1  1 2  0 0   1  1
In addition to linearizing the consumption and tax revenue functions we have
assumed a negligible influence of expected future output on consumption and
investment. Under the interest rate targeting rule, the equilibrium condition,
 =   , now yields
 =
˜ − +1 ) +  + 
0 − 1  − 2 ( −  +1 ) + (

1 − 1 (1 −  1 )
(19.54)
Consider a negative demand shock (  0). This leads to lower production and higher unemployment. Suppose people respond by prudence and
attempt to save more, say by reducing 0 and/or 1  This worsens the incipient recession and the attempt at increasing saving is defeated. The reason is
that the decreased propensity to consume lowers aggregate demand, thereby
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
reducing production. The resulting lower income brings aggregate consumption further down and so on through the renowned Keynes-Kahn multiplier
process.23 Whereas consumption is reduced, aggregate private saving is not
increased, in spite of the endeavours at the individual level to increase saving.
Indeed, aggregate private saving is
  =  − T −  =   −  − T =  +  +  − T
(19.55)

˜
and remains unchanged because  = (−
+1 ) is unchanged for fixed  What
happens is only that income is reduced exactly as much as consumption.
This is Keynes’ famous paradox of thrift. It is an example of a fallacy of
composition, a term used by philosophers to denote the error of concluding
from what is locally valid to what is globally valid. Such inference overlooks
the possibility that when many agents act at the same time, the conditions
framing each agent’s actions are affected.

By allowing consumption and investment to depend on +1
as before, the
paradox of thrift comes through in an even stronger form. In response to a
decrease in 0 and/or 1 , aggregate private saving will go down, because  on
the right-hand side of (19.55) will go down.
Digression: the loanable funds theory of the interest rate To Keynes’
conclusions that unemployment could be a state of rest and an increased
propensity to save would make things worse, many of his contemporaries
objected (for instance name, year) that the interest rate would adjust so as
to bring the demand for new loans, coming from investors, in line with an
increased supply of new loans, coming from savers. This is called the “loanable funds theory of the interest rate” according to which the interest rate
is determined by “the supply and demand for saving”. The problem with
this theory is that it does not take into account that the aggregate saving
depends not only on the interest rate, but also on aggregate income (that
the same could be said about investment is of no help for the theory).
To clarify the issue, we consider the simplest possible case where  =
( ) and  = () 0    1   0   0  =  =  − 
(no expectational errors) and where government spending and taxation are
ignored. Let  denote aggregate saving. Then in our closed economy, 
=  −  =  − ( ) ≡ ( )  = 1 −   0  = −  0
Equilibrium in the economy now requires
( ) = ()
23
Keynes (1936, pp. 113 ff.)
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(19.56)
19.5. Alternative monetary policy regimes
757
which may be interpreted as supply of saving being equilibrated with demand
for saving. Conditional on a given income level,  , we could draw an upwardsloping supply curve and a downward-sloping demand curve in the ( )
plane. But this would not determine  since the position of the supply curve
will depend on the endogenous variable,  At least one extra equation is
needed. This is what the money market equilibrium condition,  =
( ) delivers, combined with the definition  =  −  and exogeneity of
 and  Indeed, (19.56) is nothing but an IS equation since by adding
consumption on both sides of the equation, we get  = ( ) + () And
whether we combine the LM equation with this or with (19.56), the solution
for the pair ( ) will be the same.
A liquidity trap
In case of a large adverse demand shock, the IS curve may be moved so much
leftward in the IS-LM diagram that whatever the money supply, output will
end up smaller than the natural level,   Then the economy is in a liquidity
trap: conventional monetary policy can not accomplish an equilibrium close
to the natural rate. It is a trap in the sense that when the central bank
strives to stimulate aggregate demand by lowering the interest rate through
open market operations, it is like attempting to fill a leaking bucket with
water. The phenomenon is illustrated in Fig. 19.11.
The background is that the nominal interest rate has a lower bound, 0.
An increase in  can not bring  below 0. Agents would prefer holding cash
at zero interest rather than short-term bonds at negative interest. That is,
equilibrium in the asset markets is then consistent with the “=” in the LM
equation being replaced by “≥”.
When an economy is at the zero lower bound, the spending multiplier
tends to be relatively large for two reasons. The first reason is the more
trivial one that being in a liquidity trap is a symptom of a serious deficient
aggregate demand problem and low capacity utilization so that there is no
hindrance for fast expansion of production. The second reason is that there
will be no financial crowding-out effect of a fiscal stimulus as long as the
central bank maintains its policy of attempting an interest rate as low as
possible.
Note that the economy can be in a liquidity trap, as we have defined it,
before the zero lower bound on the nominal interest rate has been reached.
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
i LM M
ISe , ,G ,D P
Yn , L
Y Figure 19.11: A situation where the given IS curve is such that no non-negative
nominal interest rate can generate full employment ( +1        and 
given).
19.5.3
A counter-cyclical interest rate rule
Suppose the central bank conducts stabilization policy by using the countercyclical interest rate rule
 = 0 + 1 
1  0
(19.57)
where 0 and 1 are policy parameters and 0  if negative, is not so small that
the zero bound for  becomes topical under “normal circumstances”. This
policy rule is “counter-cyclical” in the sense of being intended to dampen
the deviations of  from its trend. The policy is counter-cyclical although
the interest rate behaves “pro-cyclically” in the terminology of business cycle
econometrics where a variable is called pro- or counter-cyclical depending on
whether its correlation with output is positive or negative, respectively.
If the LM curve in Fig. 19.8 is made linear and its label changed into
IRR (for Interest Rate Rule), that figure covers the interest rate rule (19.57).
Instead of a LM curve, we have an upward sloping IRR curve. Both  and 
are here endogenous. The fixed interest rate target from above is a limiting
case of this interest rate rule, namely the case 1 = 0. But by having 1  0
the counter-cyclical interest rate rule yields qualitative effects more in line
with those of a money targeting rule. If 1  | from (19.44), the
stabilizing response of  to a decrease in  is even stronger than under the
money targeting rule.
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19.6. Conclusion
759
Comparative statics
Inserting (19.57) into (IS) gives
 = ( 0 + 1  −  +1   ) +  +  
By taking the differential on both sides we find



1

 +1


1
1

=
∈ (0
)

1 −  −  1
1 − 
 
=
 0
1 −  −  1

= −
 0
1 −  −  1
=
= 0
We see that all multipliers become become close to 0 if the reaction coefficient
1 is large enough. In particular, undesired fluctuations due to demand shocks
are damped this way.
The corresponding changes in  are given as  = 1   for  =
   1   +1  and   respectively. From (19.53) we find the corresponding
changes in  as  =  ( + 1  )  for  =    1 , and  +1 ;
finally, from (19.53) we have again  =   0
19.5.4
Further aspects
(unfinished)
Extending the model with an interest rate spread (banks’ lending rate =
 +   )
Empirics about spending multipliers and their dependence on the state
of the economy.
Refutation of Say’s law for an economy with many industries.
19.6
Conclusion
The IS-LM framework is based on the presumption that for short-run analysis
of effects of demand shocks in an industrialized economy it makes sense, as
a first approximation, to treat the nominal price level as a predetermined
variable. This approach may build on the assumption that the wage level
is predetermined and that the marginal cost curve is horizontal. When this
is combined with constant markups due to a more or less constant price
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
elasticity of demand at firm level, a price level which is independent of output
in the short run follows. An alternative - or supplementary - rationale for the
presumed price insensitiveness builds on the menu cost theory: the idea that
there are fixed costs (pecuniary or non-pecuniary) associated with changing
prices. The main theoretical insight of the menu cost theory is that even
small menu costs can be enough to prevent firms from changing their price.
This is because the opportunity cost of not changing price is only of second
order, i.e., “small”; this is a reflection of the envelope theorem. So, nominal
prices become sticky in the short run even if marginal costs, MC, are rising.
But owing to imperfect competition (price  MC ), the effect on aggregate
output, employment, and welfare of not changing prices is of first order, i.e.,
“large”.
Traditionally, the IS-LM model has been seen as only one building block of
the more elaborate aggregate supply-aggregate demand (AS-AD) framework
of many macroeconomic textbooks. In that framework the IS-LM model
describes just the demand side of a larger model where the level of nominal wages is an exogenous constant in the short run, but the price level is
endogenous.
In this chapter we have interpreted the IS-LM model in another way,
namely as an independent model in its own right, based on the approximation
that both nominal wages and prices are predetermined in the short run;
“fixed” means set in advance by agents operating in imperfectly competitive
markets and being hesitant with regard to frequent or large price changes.
Given the pre-set wages and prices, output and employment become fully
demand-determined. Not prices on goods and services, but quantities are
the equilibrating factors. This is a complete upside-down compared with the
long-run theory of the previous chapters where output and employment were
supply-driven − with absolute and relative prices as the equilibrating factors.
Both theory and empirics support the view that when aggregate production is demand determined, the level of production and employment is
significantly sensitive to fiscal and monetary policy.
19.7
Literature notes
(incomplete)
Further examinations of the role Walras’ law and refutation of Say’s law in
macroeconomics are contained in Patinkin, D., 2008, Walras’ law, The New
Palgrave Dictionary of Economics, 2nd edition, and Malinvaud, E., 1998,
Macroeconomic Theory, Vol. B, Elsevier. The latter text gives a thorough
account of macroeconomics with quantity rationing.
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19.7. Literature notes
761
In the vocabulary of Walrasian economics, the term equilibrium is reserved to states where all markets clear unless the price in question is zero.
On this background it may be a surprise that one may talk about “Keynesian equilibrium with unemployment”. This is an established terminology
within “macroeconomics with quantity rationing”; and in Section 19.2 we
explained what is meant by “equilibrium” in this context. There is an alternative terminology where a state of affairs with involuntary unemployment is
called a disequilibrium. See for example Leijonhufvud, A. (1968), On Keynesian Economics and the Economics of Keynes, Oxford University Press, and
Herings, J. J. (1996), Static and Dynamic Aspects of General Disequilibrium
Theory, Kluwer. Although terminologies may differ, contributors to this field
of macroeconomics (Patinkin, Clower, Benassy, Grandmont, Younès, Dreze,
Malinvaud, Roberts, Böhm) seem to agree that the important aspects of
the matter are the dynamic processes triggered by clearing and non-clearing
markets.
In the wake of the development of the “menu cost theory” by Akerlof and
Yellen (1985a, 1985b) and Mankiw (1985), a path-breaking paper by Blanchard and Kiyotaki (1987) integrated (a) ideas from the quantity rationing
framework, (b) price and wage setting by market participants with market
power, and (c) the existence of menu costs in a general equilibrium model
with monopolistic competition. We return to this model in Chapter 22.
The IS-LM model was presented in a famous article by Hicks (1937) in
an attempt to summarize the analytical content of Keynes’ General Theory of Employment, Interest and Money (1936). Keynes () approved the
presentation. Of course Keynes’ book contained many additional ideas and
there has subsequently been controversies about “what Keynes really meant”
(see, e.g., Leijonhufvud 1968). But the IS-LM model has remained a cornerstone of mainstream short-run macroeconomics. The demand side of the
large macro-econometric models which governments, financial institutions,
and trade unions apply to predict macroeconomic evolution in the near future is built on the IS-LM model. Empirically the IS-LM model does a quite
good job (see Gali 1992 and Rudebusch and Svensson 1998). At the theoretical level the IS-LM model has been criticized for being ad hoc, i.e., not derived from “primitives” (optimizing firms and households, given technology,
preferences, budget constraints, and market structure). In recent years, however, more elaborate micro-founded versions of the IS-LM model have been
provided (McCallum and Nelson 1999, Sims 2000, Dubey and Geanakoplos
2003, Walsh 2003, and Woodford 2003). Some of these “modernizations” are
considered in later chapters.
To be added:
The case with investment goods industries with monopolistic competition:
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CHAPTER 19. THE THEORY OF EFFECTIVE DEMAND
Kiyotaki, QJE 1987.
Keynes 1937. Comparison between Keynes (1936) and Keynes (1939).
Balanced budget multiplier: Haavelmo (1945).
The natural range of unemployment: McDonald.
Keynes and DeLong: Say’s law vs. the treasury view.
19.8
Appendix
A. The envelope theorem
ENVELOPE THEOREM FOR AN UNCONSTRAINED MAXIMUM Let
 =  ( ) be a continuously differentiable function of two variables, of which
one, , is conceived as a parameter and the other,  as a control variable.
Let () be a value of  at which 
( ) = 0, i.e., 
( ()) = 0. Let


 () ≡ ( ()). Provided  () is differentiable,
 0 () =

( ())

where  denotes the partial derivative of ( ) w.r.t. the first argument.
Proof  0 () = 
( ()) +

= 0 by definition of (). ¤

( ()) 0 ()

=

( ()),

since

( ())

That is, when calculating the total derivative of a function w.r.t. a parameter and evaluating this derivative at an interior maximum w.r.t. a control
variable, the envelope theorem allows us to ignore the terms that arise from
the chain rule. This is also the case if we calculate the total derivative at an
interior minimum.24
B. The opportunity cost of not changing price is of second order
(no text yet available)
19.9
Exercises
24
For extensions and more rigorous framing of the envelope theorem, see for example
Sydsaeter et al. (2006).
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