TRUTH

Although a deductive argument must be valid in order to be a good argument, validity is not enough. One reason is that an argument can be valid even when some (or all) of the statements it contains are false. For example:

(1) No fathers are female. (2) Sam is a father.

(3) Sam is not female. (from 1–2)

Suppose that Sam has no children or that Sam is female, so premise 2 is false. That would be a serious defect in this argument. Nonetheless, this argument satisfies our definition of validity: If the premises were true, then the conclu- sion could not be false. There is no way that Sam could be female if Sam is a father and no fathers are female. This example makes it obvious that validity is not the same as truth. It also makes it obvious that another requirement of a good argument is that all of its premises must be true.