Here is Ludwig Wittgenstein from his Tractatus Logico Philosophicus, a seminal text on the Philosophy of Logic:
‘The Tautology is unconditionally true; the Contradiction is in no condition true…the Truth of Tautology is certain, of Proposition possible, of Contradiction impossible.
‘Tautology and Contradiction are without sense..Tautology leaves to Reality the whole infinite logical space; Contradiction fills the whole logical space and leaves no point to Reality.
Neither one of them therefore can in any way determine Reality..(They) are the limiting case of the combination of symbols, namely their dissolution.‘
O.K. So what in heaven’s name is a ‘Tautology’? I’m glad you asked. For strictly speaking, we don’t know.
What is a Contradiction? We are not too sure either.
But here are examples of what we think they mean:
‘It is raining’ is a proposition. You can verify its truth by looking out the window. ‘It is raining or not raining’ is a Tautology: it’s truth, a Logician would say, is certain. ‘It is both raining and not raining’ is a Contradiction: it’s truth, a Logician would say, is impossible.
‘It is neither raining nor not-raining’ however is Sweet Nonsense. The Logician does not see the need to dignify it with a comment.
Ludwig Wittgenstein taught Logic and Language at Cambridge with Bertrand Russell [Principia Mathematica] and was a reluctant founder of Analytical Philosophy.
I always liked Professor Wittgenstein. He was the established star at Cambridge, a serious philosopher who also had a fan-following. [Stranger things happen. Paris shut-down for Jean-Paul Sartre’s funeral.]
And Wittgenstein just turned and walked away from it all once he stopped believing in what he was teaching. That’s intellectual honesty.
In his celebrated phrase of informed and abject capitulation: ‘Whereof one cannot speak, thereof one must be silent.’