Unformatted text preview: Modus Tollens If P then Q. Not Q. Therefore, not P. Example: If the earth were flat, the hull of a receding ship would not disappear before the sails. The hull of a receding ship does disappear before the sails. Therefore, the earth is not flat. Two invalid argument forms: Denying the Antecedent If P then Q. Not P. Therefore, not Q. Example: If I owned all the gold in Fort Knox, I would be wealthy. I do not own all the gold in Fort Knox. Therefore, I am not wealthy. Affirming the Consequent If P then Q. Q. Therefore, P. Example: If Jones is gay, he supports gay rights. Jones supports gay rights. Therefore, Jones is gay....
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- Fall '07
- Logic, Modus ponens, Modus tollens, Affirming the consequent, Argument form