In logic, the contrapositive of a conditional statement is found by inverting both the antecedent and consequent and then switching their order in the relationship. For example, the contrapositive of p→q is ¬q→¬p.
A conditional statement and its contrapositive are logically equivalent. This is evident by viewing their truth table but can also be seen through example. Consider the statement all iguanas are reptiles, i→r. The contrapositive is ¬r→¬i ,or if something is not a reptile then it is not an iguana.« Back to Glossary Index