Testing for PL Validity

Abstract

It may seem that the argument whose most sophisticated PL argument consistency form was developed in the last chapter must be valid since no possible world could be such that “All heads of horses are heads of animals” would be false. Although we can perhaps not conceive of such a world, this failure of conception is not conclusive, as we can see by returning to fundamental questions about validity. We would not, for example, consider the following argument SL valid even though its conclusion is true:

Jeeves is a good butler.

Therefore, Paris is the capital of France.