Saying that an argument is valid is equivalent to saying that
it is logically impossible that the premises of the argument are
true and the conclusion false. A less precise but intuitively
clear way of putting this is to say that in a valid argument IF
the premises are true, then the conclusion must be true.
Arguments of a valid FORM are valid even if they are completely
absurd. For example, the following argument is valid:
All women are cats.
This argument has false premises and a false conclusion. This
brings out the hypothetical character of validity. What the validity
of these arguments amounts to is that it assures us the conclusion
must be true IF the premises are true.
All cats are men.
All women are men.
If an argument can be valid and yet have a preposterously false
conclusion, what good is validity? Why should we be concerned
with validity at all? The answer is that a valid argument is
truth preserving. Truth in the premises of a valid argument is
preserved in the conclusion. Of course, if the premises are not
true to begin with, then even a valid argument cannot ensure that
the conclusion is true. But ONLY valid arguments are truth preserving.
An analogy might help clarify this point. Roughly, valid arguments
preserve truth like good freezers preserve food. If the food
you place in a freezer is spoiled to begin with, then even a good
freezer cannot preserve it. But if the food placed in a good
freezer is fresh, then the freezer will preserve it. Good freezers
and valid arguments preserve food and truth, respectively. But
just as the former cannot preserve food when the food is spoiled,
so the latter cannot preserve truth when the premises are false.
Nevertheless food freezers and valid arguments are worth having
because they do preserve something good when one has it, and without
them one may wind up with something rotten even when beginning
with something impeccable. Thus validity is to be desired and
invalidity is to be eschewed.