Download Argument - University of Warwick

Philosophy in Practice
Simon Scott
Room S2.49
Email: [email protected]
Critical reasoning lectures
Reading: Kemp and Bowell, Critical Thinking: A Concise
Guide, 2nd or 3rd edition.
In course-handbook-speak:
To equip you with the concepts and techniques required to identify,
reconstruct, and evaluate arguments.
In more down-to-earth-language:
To make you better at assessing the attempts people make to
persuade you to do/believe certain things, and to become better at it
yourself.
The first 3 lectures
Lecture One: introduces you to some basic concepts
required for assessing attempts to persuade:
arguments, validity, soundness
Lecture Two: equips you with the skills needed for
identifying and reconstructing arguments.
i.e., knowing how people are trying to persuade you
Lecture Three: equips with the skills needed for
evaluating arguments.
i.e., knowing whether these attempts to persuade are
any good.
Good reasons?
“You should take Philosophy at university. Why? Because the
study of philosophy equips graduates with all sorts of
analytical, critical, and verbal skills. Not only does this help
them succeed at university, but it also makes them extremely
attractive to potential employers: the civil service, banking,
journalism, to name but a few. More generally, studying
philosophy makes you smarter: there are numerous studies
showing that philosophy students come out top along a
whole host of parameters as compared to students from
other subjects.”
Tasks of the Critical Thinker
Argument: the attempt to persuade by giving reasons.
Two main tasks of the critical thinker:
(a) Distinguish argumentative and non-argumentative attempts
to persuade.
(b) Assess whether arguments do in fact succeed in providing
you with good reasons for believing/acting.
Being able to do (a) and (b) means that you are a critical thinker.
Arguments vs. unsupported claims
One very basic skill in critical thinking is being able to
differentiate arguments from unsupported claims...
Arguments involve giving reasons.
You can think of giving reasons as essentially providing
support for the thing you are arguing for.
So an argument will always involve at least one claim being
offered in support of another claim; the former is to
provide reasons for believing that the latter is true.
Arguments vs. unsupported claims
Here is an unsupported claim:
“I think that gay marriage is something that
should be between a man and a woman.”
(Arnold Schwarzenegger, Aug 27th, 2003)
Arguments vs. unsupported claims
“Marriage should be between a man and a woman.
Thousands of years of history and tradition underpin this
principle. We should not ignore our heritage. Marriage is
also a reflection of the biological necessity of one-to-one
sexual union for procreation and the raising of children.
Same sex-couples can’t have children.”
(one of the standard arguments against gay-marriage)
Key point: regardless of whether you think this is any good as
an argument, there is at least an attempt being made to
offer reasons.
Arguments vs. unsupported claims
“I’ve always opposed gay marriage. I believe that we
should provide equal rights to people regardless of
their sexual orientation but I do not believe that
marriage should be between two people of the same
gender.”
(Mitt Romney, Jan 16th, 2012)
Diagnosis: the ‘reasons’ being offered in support are
essentially a restatement of the thing being argued for.
A poor attempt to persuade.
Arguments or unsupported
assertions?
(a)People who don’t support our operations in Iraq are
unpatriotic and want our troops to fail. (unsupported)
(b)Despite repeated attempts, no-one has ever come up
with a proof of God’s existence. Hence, we can
conclude that God doesn’t exist. (argument)
(c)If we deal with the nation’s debt quickly and decisively
then we will provide the basis for a more secure
economic future. (unsupported)
(d)Backwards time-travel is impossible. If it were at all
possible then people from the future would have
visited us. But as we all know, this has never
happened. (argument)
Arguments
Arguments have two components:
(i) The supporting claims (premises)
(ii) The claim for which the supporting claims are being given
(conclusion)
This enables us to formulate a more precise definition of what an
argument is:
Argument: a set of propositions, one of which is the conclusion,
and the remainder are premises. The premises are intended to
support (provide reasons for) the conclusion.
Propositions
‘The snow is white’ and ‘La neige est blanche.’
In more precise language: these sentences have the same
factual content.
That is, they both depict the world in a certain way that
could be either true or false: depending on what colour
the stuff is that falls in winter.
The factual content = the proposition expressed by the
sentence.
Propositions
Proposition: the factual content expressed by a declarative
sentence (or utterance, if spoken), on a particular occasion.
Propositions can be true or false.
Different sentences can express the same proposition. (e.g.,
‘The snow is white’ and ‘La neige est blanche’)
The same sentence can express different propositions. (e.g.,
‘I saw her duck’)
Arguments
A slightly more refined definition of an argument:
Argument: Arguments are sets of propositions (which
can be true or false), one of which is the conclusion,
and the remainder are premises. The truth of the
premises is intended to support the truth of the
conclusion.
Standard form
The clearest way to set out an argument is to put it into what
is called Standard Form.
This involves setting out the premises in the order that the
occur in the reasoning, and then the conclusion, with an
inference bar separating the two (signifying therefore).
P1: If backwards time travel were possible, then people
would have come back from the future to visit us.
P2: People haven’t come back from the future to visit us.
--------------------------------------------------------------------------------C: Backwards time travel is impossible.
standard form
Note the contrast with:
“Backwards time-travel is impossible. The reasons for
thinking this are obvious. If it were at all possible then
people from the future would have visited us. But as we
all know, this has never happened.”
- The move from this to the same argument in standard
form is called a reconstruction.
- Part of being a good critical thinker is being able to
reconstruct arguments into standard form.
Reconstructing an argument
•
•
•
•
First, identify whether there is an argument(s)
Identify the conclusion
Identify the premises of the argument(s)
Reconstruct the argument in standard form
•
•
•
•
Number the premises and write them out in order
Draw in the inference bar
Write out the conclusion
Evaluate the argument
Descartes’ indivisibility argument
“There is a great difference between the mind and the
body, inasmuch as the body is by its very nature always
divisible, while the mind is utterly indivisible. For when I
consider the mind, or myself in so far as I am merely a
thinking thing, I am unable to distinguish any parts within
myself; I understand myself to be something quite single
and complete…
By contrast, there is no corporeal or extended thing
that I can think of which in my thought I cannot easily
divide into parts; and this very fact makes me understand
that it is divisible.
This one argument would be enough to show me that
the mind is completely different from the body…”
(Descartes, Meditations, Meditation 6)
Descartes’ indivisibility argument
P1: The mind is by its very nature indivisible.
P2: The body is by its very nature divisible.
--------------------------------------------------------------------------------C1: The mind and body have different properties.
P3: X is identical to Y if, and only if, for any property had by X
at time t, Y also has that property at time t (and vice versa).
--------------------------------------------------------------------------------C2: The mind and the body are distinct.
What makes a good argument?
There are two ways in which an argument might
succeed:
1. There might be a particularly tight connection
between the supposed truth of the premises and
the truth of the conclusion (related to the idea of
the premises supporting the conclusion).
2. The premises are in fact true.
Focus on (1)
Deductive validity
A more specific way of cashing out (1) is to say that a good
argument will be deductively valid.
Deductive Validity: an argument is deductively valid just
in case it would be impossible for the premises to all be
true but for the conclusion to be false.
Alternatively:
Deductive Validity: to say that an argument is
deductively valid is to say that if the premises were all
true, then the conclusion would have to be true.
Both definitions amount to the same thing
Deductive validity
P1: The prime minister’s dog is infested with fleas.
P2: All fleas are bacteria.
-------------------------------------------------------------------C: The prime minister’s dog is infested with bacteria.
Valid argument
P1: Colette owned a dog.
P2: All French bulldogs are dogs.
---------------------------------------------------------------------C: Colette owned a French bulldog.
Invalid argument
Invalidity
Invalidity is just the negation of validity:
Invalidity: an argument is invalid just in case it is
possible for the premises to all be true and for the
conclusion to be false.
Alternatively:
Invalidity: to say that an argument is invalid is to say
that if the premises were all true, then the conclusion
need not be true.
Both definitions amount to the same thing.