PHIL 100 Lecture Notes - Lecture 6: Categorical Proposition, If And Only If
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Denying the antecedent: if p, then q, ~p, ~q. Affirming the consequent: if p, then q, q, p. Argument by elimination: either p or q, ~p, q. Affirming the antecedent: if p, then q, p, q. Denying the consequent: if q, then r, ~r, ~q. Hypothetical syllogism: if p, then q, if q, then r, if p, then r. Contraposition: if p, then q, if ~q, then ~p. Equivalence: p if and only if q, ~p, ~q. If p is true, it doesn"t follow that s is justified in believing p. If s is justified in believing p, it does follow that p is true. 2. invalid: test for invalidity by assuming that all premises are true and seeing whether it is still possible for the conclusion to be false. If this is possible, the argument is invalid. (12) if [antecedent], then [consequent] In a true conditional, if the antecedent is true, so is the consequent.
