The Language of Argument

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Refutation by Parallel Reasoning

REFUTATION by PARAllEl REASONINg

Even if its premises and conclusion cannot be refuted by any counterexam-

ple or reductio, a deductive argument can also be refuted by showing that

it is invalid. We know that an argument is not valid if it starts from true

premises and leads to a false conclusion. Often, however, we cannot point

this out to refute an argument, because the truth or falsity of the conclusion

is the very thing at issue. When this problem arises, a typical device is to

point out that by arguing in the same way, or a similar way, we can reach a

conclusion that is unsatisfactory.

Here is a simple example:

Cary: Most of the people in this class are college students. Most college

students study hard. Therefore, most of the people in this class study

hard.

David: That’s just like arguing that most whales live in the sea, and most

animals that live in the sea are fish, so most whales are fish.

At first sight, it might not be clear how the second argument could show

anything about the first argument. What do whales have to do with students?

The point, however, is simply that the two arguments share a basic form:

Most As are Bs, and most Bs are Cs, so most As are Cs. Thus, if the second

argument is not valid by virtue of that form, then the first is also not valid by

virtue of that same form. The second argument is obviously not valid, since

its premises are true but its conclusion is false. This shows that the first argu-

ment is not valid, at least by virtue of this shared form. Even though the first

argument still might be valid on some other basis, its defenders at least owe

an alternative account of its validity. Often there will be none.

Refuting an argument by showing that it is just like another argument that

is obviously no good is a common device in everyday discussions. Here’s

another example:

matthew: If I had a higher salary, I could buy more things; so, if

everyone had higher salaries, everyone could buy more things.

Kirsty: That’s just like arguing that, if one person stands up at a ball

game, he will get a better view; so, if everyone stands up, everyone

will get a better view.

At first sight, it may not be obvious whether Matthew’s style of reasoning

is valid or not. Kirsty’s response shows that Matthew’s argument is invalid

by providing an instance in which the same style of reasoning takes us

Find five more examples of attacking straw men in your local newspaper, in a

talk show on television, or in a college course.

Discussion Question

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