Wittgenstein is to be credited with the invention or at least the popularization of truth tables (4.31) and truth conditions (4.431) which now constitute the standard semantic analysis of first-order sentential logic. The philosophical significance of such a method for Wittgenstein was that it alleviated a confusion, namely the idea that logical inferences are justified by rules. If an argument form is valid, the conjunction of the premises will be logically equivalent to the conclusion and this can be clearly seen in a truth table; it is "displayed". The concept of tautology is thus central to Wittgenstein's Tractarian account of logical consequence, which is strictly deductive.