"Proof in logic is merely a mechanical expedient to facilitate the recognition of tautologies in complicated cases."
"The propositions of logic are tautologies. Therefore the propositions of logic say nothing. "
"What belongs to its application, logic can not anticipate."
"And this is what we do, when we "prove" a logical proposition. For, without bothering about sense or meaning, we construct the logical proposition out of others using rules that only deal with signs."
Ludwig Wittgenstein --Tractatus Logico-Philosophicus