4.464 The truth of tautology is certain, of propositions possible, of contradiction impossible.

(Certain, possible, impossible: here we have an indication of the gradation we need in the theory of probability.)

It’s dodgy though, isn’t it? The certain must belong to the class of the possible, surely, not be a separate class from it.

No article before “tautology” or “contradiction” here, or in 4.463, as per Wittgenstein’s wishes in Letters to Ogden, p. 30. No plural because “there are in fact no contradictions but there is only contradiction, for they all mean the same, i.e. nothing. And the same applies to tautology.”