Download Kripke, A Priori Knowledge, Necessity and Contingency

Being and Knowledge
Handout on Kripke
Kripke on Necessity, Contingency and the A Priori
A. The Classic Connections
TYPE
“Type” is a way of discerning
what the parts of the proposition
encompassing the judgment refer
to.
Proposition is
composed of
concepts;
Analytic
judgment about
relations
between those
concepts
METHOD
The epistemic way in which
that judgment can be
discerned as true or false.
A Priori
The judgment
contained
within the
proposition is
known via
reason alone.
STATUS
The status of the truth of the
judgment known.
Necessary
True in all
possible worlds.
The classic understanding sees these as all connected via biconditionals. So:
(X is analytic IFF X is a priori) and (X is apriori IFF X is necessary)
Proposition is
The judgment
composed of
contained
terms referring
within the
to sense
proposition is
Synthetic
contents;
A Posteriori
known
Contingent
judgment is
through some
about relations
form of
between those
sensation.
contents
The classic understanding sees these as all connected via biconditionals. So:
False in some
possible world.
(X is synthetic IFF X is a posteriori) and (X is a posteriori IFF X is contingent)
Note: Kant attacks the left conjunct here himself, suggesting that some synthetic statements are a priori.
B. Some Vocabulary
Some vocabulary:
a. Rigid Designator (RD): names refer to the same object in all PW. (ex. “Aristotle was the
student of Plato”). So the relation between the name and its “referent” is one of necessity.
b. Strongly Rigid Designator: (SRD): a name that refers to an object that does exist in all PW.
c. Definite Description (DD): a description used to give a “sense” to a name, or a way of
accessing what the name points to (ex. “Aristotle was the student of Plato”). What a DD points
to in a given world may not be what it points to in another PW. So the relation between a DD and
what it allows you to point to is one of contingency (DD’s are non-rigid designators).
C. Kripke’s Claim: metaphysics (necessity) and epistemology (a prioricity) are different concepts.
As a result, they come apart.
Note that if they did not come apart, this biconditional would be true:
X is necessary if and only if X is a priori
Since Kripke thinks that the two are totally different concepts, he wants to argue that the
biconditional is false. Since this is a biconditional, it has two parts:
1. If X is necessary, then X is a priori
This conditional seems intuitive; it seems to be the case that if something necessary is the case,
then you cannot learn about it by observation of the world. This is an old dogma taken as
obvious since the modern philosophy period (especially Hume). Kripke will argue that some
necessary truths are known a posteriori.
2. If X is a priori, then it is necessary
This again seems true, and has been classically taken as obvious, namely that a truth that is
known through reason alone cannot be contingent. Yet, Kripke will argue that some a priori
truths are contingent.
C1. Argument One: Some Necessary Truths are known through Experience
Let’s take some identity statements, and assume they are all true (they are):
1.
2.
3.
4.
Hesperus = the star right there in the morning sky.
Phosphorus = the star right there in the evening sky.
The star right there in the morning sky = the star right there in the evening sky.
Hesperus = Phosphorus
Claim one: the truth of (4) is a posteriori.
Knowing (1) and (2) does not entail knowing (3) or (4). It seems that even if (1) and (2) are true,
there is no a priori way of knowing that what was pointed to in the two different situations was
the same object. As a result, knowing (4) must be known a posteriori, or by empirical
investigation.
Claim two: the truth of (4) is necessary.
Of course, this claim follows from the claims about rigid designators. But let’s think about the
argument.
1. Suppose that X = Y
2. ‘X’ refers to P in all possible worlds (names are rigid designators)
3.
4.
5.
6.
‘Y’ refers to P in all possible worlds (names are rigid designators)
So, X = Y if and only if P = P (from (1) to (3)
Necessarily, P = P (an object is what it is, and nothing besides!)
So, necessarily, X = Y
If this is right, the truth of (4) is necessary. But we also saw that the truth of (4) is known a
posteriori. Result: some necessary truths are a posteriori.
C2. Argument Two: Some a Priori Truths are Contingent
Kripke uses the example of the standard meter stick in Paris (the one in the museum).
1. The King said (at some point), “Stick S at t (that one over there, right now) is one meter long”.
2. “Stick S is one meter long” is true.
Claim One: the truth of (2) is known a priori.
Think about this claim. How is its truth fixed? Note, and remember here, that the stick itself is
the fiat determiner of what “one meter” is. So you can’t claim that you learned via empirical
investigation that the stick is one meter long. As a result, the claim must be a priori.
Claim Two: the truth of (2) is contingent.
3. “One Meter” is a rigid designator.
4. “Stick S at t” is a definite description.
If (3) and (4) are true, then “Stick S at t” is really a way of indicating something, it’s a way of
pointing to something (in this case, “one meter”). Because we know that DD do not point to the
same things in all possible worlds, it is possible that Stick S at t could point to a very different
length in another world. As a result, “Stick S at t is one meter” is a contingent truth.
Thus, some a priori claims are contingent.