modus tollens

logic

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June 30, 2026

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Modus tollens is a fundamental rule of inference in propositional logic. It is a method of reasoning that follows a specific structure: If a hypothetical proposition is true (If A, then B), and its consequent is false (not B), then its antecedent must also be false (therefore, not A).12

For example: If an angle is inscribed in a semicircle, then it is a right angle. This angle is not a right angle; therefore, this angle is not inscribed in a semicircle. This form of reasoning is crucial in constructing valid arguments and understanding logical relationships.1

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modus ponens and modus tollens
modus tollens, in propositional logic, two types of inference that can be drawn from a hypothetical proposition—i.e., from a proposition of the form “If A, then B” (symbolically A ⊃ B, in which ⊃ signifies “If . . . then”). Modus ponens refers to inferences…
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modus tollens, in propositional logic, two types of inference that can be drawn from a hypothetical proposition—i.e., from a proposition of the form “If A, then B” (symbolically A ⊃ B, in which ⊃ signifies “If . . . then”). Modus ponens refers to inferences…
Read More