"If
is true, and
is true, then
is true."
From this apparatus the whole theory of deduction follows, except in so far as we are concerned with deduction from or to the existence or the universal truth of "propositional functions," which we shall consider in the next chapter.
There is? if I am not mistaken, a certain confusion in the minds of some authors as to the relation, between propositions, in virtue of which an inference is valid. In order that it may be valid to infer