Deviant logics reject standard assumptions. Most logicians have assumed that statements are either true or false, but not both, and that true and false are the only truth values. Deviant logics question such ideas. Maybe we need more than two truth values (many-valued logic). Or maybe “A” and “not-A” can both be true (paraconsistent logic) or both be false (intuitionist logic). Or maybe standard IF-THEN inferences are mistaken (relevance logic).