n.
In logic , a statement that cannot be denied without inconsistency.
Thus, "All bachelors are either male or not male" is held to assert, with regard to anything whatsoever that is a bachelor, that it is male or it is not male. In the propositional calculus , even complicated symbolic expressions such as [(A 2283; B) 2227; (C 2283; 00AC; B)] 2283; (C 2283; 00AC; A) can be shown to be tautologies by displaying in a truth table every possible combination of T (true) and F (false) of its arguments A, B, C. A tautology can be purely formal (a statement form rather than a statement), and in some usages only such formal truths are tautologies.