The Language of Argument

9 1

so m e st a n d a r d s f o r ev a l u a t i n g A r g u m e n t s

argument for assuming something that it does not really need to assume.

Nonetheless, if an argument does need to meet certain standards in order

to support its conclusion, then it is legitimate to add premises that really

are necessary for the argument to meet those standards. Thus, in order to

determine which assumptions we can fairly ascribe to an argument, we first

need to determine precisely which standards that argument needs to meet in

order to succeed or be good.

Evaluating arguments is a complex business. In fact, this entire book is

aimed primarily at developing procedures for doing so. We will find that

different standards apply to different arguments. There are, however, cer-

tain basic terms used in evaluating many arguments that we can introduce

briefly now. They are validity, truth, and soundness. Here they will be in-

troduced informally. Later (in Chapters 6 and 7) they will be examined with

more rigor.

Validity

In some good arguments, the conclusion is said to follow from the premises.

However, this commonsense notion of following from is hard to pin down

precisely. The conclusion follows from the premises only when the content

of the conclusion is related appropriately to the content of the premises, but

which relations count as appropriate?

To avoid this difficult question, most logicians instead discuss whether an

argument is valid. Calling something “valid” can mean a variety of things,

but in this context validity is a technical notion. Here “valid” does not mean

“good,” and “invalid” does not mean “bad.” This will be our definition of

validity:

An argument is valid if and only if it is not possible that all of its premises

are true and its conclusion false.

Alternatively, one could say that its conclusion must be true if its premises

are all true (or, again, that at least one of its premises must be false if its con-

clusion is false). The point is that a certain combination—true premises and

a false conclusion—is ruled out as impossible.

The following argument passes this test for validity:

(1) All senators are paid.

(2) Sam is a senator.

∴(3) Sam is paid. (from 1–2)

Clearly, if the two premises are both true, there is no way for the conclusion

to fail to be true. To see this, just try to tell a coherent story in which every

single senator is paid and Sam is a senator, but Sam is not paid. You can’t

do it.

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