Contraposition

Part of speech: noun

Pronunciation: /ˈkɒntɹəpəˈzɪʃən/

Definitions

1. A method used in logic that involves reversing and negating the components of a conditional statement, thereby yielding an equivalent proposition
2. A logical technique that alters a conditional statement by switching and negating both terms to arrive at a valid equivalent form
3. The process in logic of forming an equivalent proposition by interchanging the hypothesis and conclusion of a conditional statement and negating both

Etymology: "Contraposition" arrived in English from French "contraposition," itself built from Latin roots: "contra," meaning "against" or "opposite," and "positio," meaning "placing" or "position." The literal sense is therefore a placing-against, or a setting of one thing opposite another. The logical sense grows from that spatial picture. In traditional logic, a conditional such as "if it rains, the ground is wet" is turned around by swapping its two parts and negating both, giving "if the ground is not wet, it is not raining." The new statement is placed opposite the old one, and the two stand or fall together. The term thus keeps the original image of two positions facing each other, now applied to propositions rather than objects.

Synonyms: reversal, opposition