Reason and Argument
Chapter 7
BASIC RULES OF ARGUMENT EVALUATION
If, after a proper reconstruction, the argument is not well-formed, then it is
enough to demonstrate that the argument is ill-formed -- no further evaluation is
necessary.
From this point forward, we assume that the argument to be evaluated is wellformed.
A. Don’t criticize an argument by denying its conclusion.
The principle of Good Criticism (GC): A good criticism of a well-formed argument
must either show that the argument is defeated or has an unjustified premise.
Example:
1. If God exists then no babies are born with cancer.
2. Some babies are born with cancer.
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3. It is not the case that God exists.
Bad criticism: “I know the argument is wrong because I know that God exists.”
Variations on this theme, such as “I have faith that God exists” are no good as
criticisms either.
B. Don’t accept an argument simply because you believe the conclusion.
Example:
1. If the earth is not round, then the vast majority of people are all wrong.
2. The vast majority of people can’t all be wrong.
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3. Therefore, the earth is round.
C. If the argument is valid, direct criticisms at individual premises.
If the argument is valid, then criticizing it’s premises is the only legitimate way to
criticize it. If the argument is cogent, it is also possible to criticize the argument
by citing evidence that defeats it. In general, it is not a good criticism of an
argument to present a competing argument without addressing the argument
itself.
D. Make your criticisms of premises substantial.
Claiming that a premise might be false is not a substantial criticism. To show
that the premise is not justified, you have to show that it is at least as likely to be
false as it is to be true.
Likewise, argument stoppers are not substantial criticisms. For example, if one
says, “Who’s to say that’s true?” then the arguer can quite properly reply “I’m
saying it’s true.” Asking a rhetorical question does nothing to undermine the
premise.
Also, noting that something is a matter of opinion does nothing to undermine it.
Some opinions turn out to be right, others wrong. Some opinions are better
supported than others. The fact that something is a person’s opinion does not
cast doubt on it.
E. Don’t accept competing arguments.
By definition, competing arguments can’t both be right, so it is irrational to accept
both (however, competing argument can both be wrong, so it may be rational to
reject both). It may be appropriate to withhold judgment in cases where
competing arguments both appear to be strong. However, they cannot both
literally be strong for you.
F. Don’t object to intermediate conclusions of compound arguments.
This is a corollary of C. Intermediate conclusions are conclusions in their own
right. Since they follow from other premises, you should direct your criticism at
one or more of those premises.
G. Don’t assume that an argument is strong just because each premise is
more than 50% likely.
An argument is strong only if the conjunction of all of the premises is more than
50% likely. See lottery paradox, and argument on p. 182
II. EVALUATING SPECIFIC TYPES OF PREMISES
A. Specific factual claims.
B. Generalizations.
Universal Generalizations – refuted by counter-examples
“near all” generalizations – cases where the generalization doesn’t hold are
significant, but not usually decisive
For all other generalizations, other methods must be used. For example, you
could refute a “some A’s are B’s” generalization by giving a strong argument to
the effect that “No A’s are B’s”.
C. Compound Sentences.
Conjunctions
Disjunctions
Inclusive versus exclusive
False dilemmas
Problems with conjoining premises (lottery paradox, and argument on p. 182)
Necessary and sufficient conditions, definitions and conditionals.
Ambiguity. Example of an argument that depends on ambiguity (not from the
text):
Professor Warren considers the following anti-abortion argument:
1) It is wrong to kill innocent human beings.
2) Fetuses are innocent human beings.
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3) Therefore, it is wrong to kill fetuses.
She claims that the plausibility of the premises rest on an equivocation on the
term ‘human being’:
Human in the genetic sense = being a member of the biological species homo
sapien.
This includes not only functioning children and adults, but also includes
fetuses (even very early fetuses) and living human bodies without
functioning brains (e.g. those in irreversible comas).
Human in the moral sense = being a full-fledged member of the moral
community.
The moral community is the set of beings with full moral rights, and
consists of all and only persons.
If ‘human being’ has the same sense in both premises then one of them is
question-begging. Either the argument assumes that it is wrong to kill something
merely because it is homo sapien, or the argument assumes that a fetus is a
member of the moral community. Both of these claims are contentious and
would require further argument.
Exercises p. 201
2.
1. All free countries allow people to drive more than 55 mph on all of the
highways.
2. The U.S. does not allow people to drive more than 55 mph on all of the
highways.
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3. The U.S. is not a free country.
Implicit definition:
Free country =df a country where citizens can do whatever they want.
Better definition:
Free country =df a country where civil rights, such as the right of free speech, the
right to vote, and the right to congregate, are respected and enforced.
4.
1. All altruistic acts are acts that are harmful to the person who performs them
and helpful to others. (EP)
2. If evolutionary theory is true, then people always act to maximize chances for
survival. (EP)
3. Evolutionary theory is true. (IP)
4. People always act to maximize chances for survival. (2,3)
5. No act that maximizes chances for survival is an act that is harmful to the
person who performs it. (IP)
6. Therefore, no act that maximizes chances for survival is an act of altruism
(1,5)
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6. Therefore, people never act altruistically. (4,6)