Modus tollens
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Modus tollens ("mode of taking") is a logical argument, or rule of inference. (Compare with modus ponens, or "mode of putting.")
[edit] As an argument
A modus tollens argument has the following form:
- P1: If X, then Y.
- P2: Not Y.
- C1: Therefore, not X.
For example:
- P1: If it is raining, the ground is wet.
- P2: The ground is not wet.
- C1: Therefore, it is not raining.
[edit] As a rule of inference
In propositional logic:
In first-order logic:
[edit] External links
- See the Wikipedia article on Modus tollens.