contrapositive

Noun

 * 1)  The inverse of the converse of a given logical implication.

Usage notes

 * From a conditional statement, its inverse, its converse, and its contrapositive are defined as follows:
 * Proposition: "If P then Q."
 * Inverse: "If not P then not Q."
 * Converse: "If Q then P."
 * Contrapositive: "If not Q then not P."
 * If a conditional statement is true then its contrapositive is, too. Thus, if the statement "If I'm Roman, then I can speak Latin" is true, then it logically follows that the statement "If I can't speak Latin, then I'm not Roman" must also be true.
 * In (more generally, logics employing the law of excluded middle), a conditional statement is true if and only if its contrapositive is true. In this framework, if the statement "If I can't speak Latin, then I'm not Roman" is true, then the statement "If I'm Roman, then I can speak latin" must also be true

Translations

 * Finnish: kontrapositio
 * German: Kontraposition
 * Icelandic: mótskilyrðing