That e.g. the propositions “p” and “\~p” in the connexion “\~(p . \~p)” give a tautology shows that they contradict one another. That the propositions “p ⊃ q”, “p” and “q” connected together in the form “(p ⊃ q) . (p) : ⊃ : (q)” give a tautology shows that “q” follows from “p” and “p ⊃ q”. That “(x) . fx : ⊃ : fa” is a tautology shows that fa follows from (x) . fx, etc. etc.