(Lat., reduction to absurdity) The process of reasoning that derives a contradiction from some set of assumptions, and concludes that the set as a whole is untenable, so that at least one of them is to be rejected. Formally, if A1…An ⊦ (B & ¬B), then A1…An-1 ⊦ ¬An.
Philosophy dictionary. Academic. 2011.