In traditional logic, obversion's a "type of immediate inference in which from a given proposition another proposition's inferred whose subject's the same as the original subject, whose predicate's the contradictory of the original predicate, and whose quality's affirmative if the original proposition's quality was negative and vice versa". The quality of the inferred categorical proposition's changed but the truth value's equivalent to the original proposition. The immediately inferred proposi… (More on Obversion)