contraposition

logic

Also known as: contrapositive

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July 23, 2026

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In logic, contraposition refers to the relationship between two propositions where the subject and predicate of one are the negations of the predicate and subject of the other. A contrapositive is a proposition formed by negating and interchanging both the subject and predicate of a given proposition.12

For example, the contrapositive of "If A, then B" is "If not B, then not A". This means that if the second part of a statement is false, then the first part must also be false. The two propositions involved in contraposition are called contraposita. This is different from a converse, which simply interchanges the subject and predicate without negation.234

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syllogistic
…type of inference is called contraposition and is produced by the fact that some propositions imply the proposition that results from the original proposition when both of its term variables are negated and their order reversed.
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…type of inference is called contraposition and is produced by the fact that some propositions imply the proposition that results from the original proposition when both of its term variables are negated and their order reversed.
Read More