Reductio ad absurdum

An argument that concludes the negation of a proposition, on the grounds that a contradiction can be derived from that proposition. “Reductio ad absurdum” is literally “reduction to absurdity.” Here, “absurdity” is a contradiction. A reduction argument involves demonstrating that a certain assumption yields a contradiction. (See also Contradiction introduction,Modus tollens, Negation introduction, Indirect proof, and Proof by contradiction.)