. Between "
implies not-
" and "
implies not-
" there is a formal relation which enables us to know that the first implies the second, without having first to know that the first is false or to know that the second is true. It is under such circumstances that the relation of implication is practically useful for drawing inferences.
But this formal relation is only required in order that we may be able to know that either the premiss is false or the conclusion is true. It is the truth of "not-