that every proposition possesses one of these properties. This now by no means appears self-evident, no more so than the proposition "All roses are either yellow or red" would sound even if it were true. Indeed our proposition now gets quite the character of a proposition of natural science and this is a certain symptom of its being falsely understood.
6.112 The correct explanation of logical propositions must give them a peculiar position among all propositions.
6.113 It is the characteristic mark of logical propositions that one can perceive in the symbol alone that they are true; and this fact contains in itself the whole philosophy of logic. And so also it is one of the most important facts that the truth or falsehood of non-logical propositions can not be recognized from the propositions alone.
6.12 The fact that the propositions of logic are tautologies shows the formal—logical—properties of language, of the world.
That its constituent parts connected together in this way give a tautology characterizes the logic of its constituent parts.
In order that propositions connected together in a definite way may give a tautology they must have definite properties of structure. That they give a tautology when so connected shows therefore that they possess these properties of structure.
6.1201 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".