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A proposition derived by negating and permuting the terms of another, equivalent proposition; for example, All not-Y is not-X is the contrapositive of All X is Y.
(Logic) placed opposite or against
a. a conditional statement derived from another by negating and interchanging antecedent and consequent
b. a categorial proposition obtained from another, esp validly, by any of a number of operations including negation, transferring the terms, changing their quality, and also possibly weakening from universal to particular
con•tra•pos•i•tive(ˌkɒn trəˈpɒz ɪ tɪv)
1. of or pertaining to contraposition.n.
2. a contrapositive statement.