or
" that is required for the validity of the inference; what is required further is only required for the practical feasibility of the inference. Professor C. I. Lewis[37] has especially studied the narrower, formal relation which we may call "formal deducibility." He urges that the wider relation, that expressed by "not-
or
" should not be called "implication." That is, however, a matter of words. Provided our use of words is consistent, it matters little how we define them. The essential point of difference between the theory which I advocate and the theory advocated by Professor Lewis is this: He maintains that, when one proposition
is "formally deducible" from another