Contraposition

Con"tra*po*si"tion (?), n. [Pref. contra- + position: cf. f. conterposition.] 1. A placing over against; opposite position. [Obs.] F. Potter.

2. (Logic) A so-called immediate inference which consists in denying the original subject of the contradictory predicate; e.g.: Every S is P; therefore, no Not-P is S.