Ever since I was engaged on Principia Mathematica, I have had a certainmethod of whichat first Iwasscarcely conscious, but which has gradually become more explicit in my thinking. The method consists in an attempt to build a bridge between the world of sense and the world of science.
Omnium Rerum Principia Parva Sunt."
...a theorem of propositional logic if and only if f(p1, p2 ,..., pn) is a tautology . ... He (Emil L.Post) uses the word to discuss the adequacy of a system of functions to express all the possible truth tables (this is nowadays called truth-functional completeness). In this way he shows not only that through the connectives of Principia (? and ?) one can generate all possible truth tables but also that there are only two connectives which can, singly generate all the truth tables.