:For the mathematical form of proof by contradiction, see Proof by contradiction.
Reductio ad absurdum (Latin: "reduction to the absurd") is a form of argument in which a proposition is disproven by following its implications logically to an absurd consequence.
A common species of reductio ad absurdum is proof by contradiction (also called indirect proof) where a proposition is proved true by proving that it is impossible for it to be false. For example, if A is false, then B is also false; but B is true, therefore A cannot be false and therefore A is true. In practice such arguments are f...