100-07-08 Evaluating Deductive Arguments

100-07-08 Evaluating Deductive Arguments - P&A,...

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Evaluating Deductive Arguments DEDUCTIVE and INDUCTIVE ARGUMENTS Deductive arguments are those in which the truth of the premises guarantees the truth of the conclusion ( 10; DP, 77). All other arguments can be called inductive; in inductive arguments the truth of the premises makes the truth of the conclusion more likely or probable ( DP, 77). VALIDITY AND SOUNDNESS Deductive arguments are valid if and only if the truth of the premises guarantees the truth of the conclusion ( P&A, 12). That does not mean that the premises are true, but rather that if the premises are true, the conclusion must be, example, 12) . A valid argument is sound when the premises are true (13). SOME COMMON, VALID ARGUMENT FORMS Validity does not depend on the content of the propositions involved in an argument, but on the form of the argument. There are some common forms of valid arguments displayed in
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Unformatted text preview: P&A, 14-21; the mistakes people frequently make are also displayed. Valid Argument Form Corresponding Mistake 1. Modus Ponens Fallacy affirming the Consequent If p then q If p then q p q Therefore, q Therefore, p 2. Modus Tollens Fallacy of Denying The Antecedent If p then q If p then q If p then q Not q Not p Therefore, not p Not q 3. MPT Conjunctive Fallacy Not (p and q) Not (p and q) Not (p and q) p q Not p Therefore, not q Therefore, Not p Therefore, q 4. MTP Disjunctive Fallacy p or q p or q p or q Not p not q p Therefore, q Therefore, p Not q Conjunction Introduction p q Therefore, p and q (and q and p) Conjunction Elimination P and q Therefore, P (and q) Disjunction Introduction p ( or q) Therefore, p or q Double Negation p Not not-p Therefore, not not-p Therefore, p Note summary of logical consequences 20....
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This note was uploaded on 04/18/2008 for the course PHL 100 taught by Professor Boyle during the Spring '08 term at University of Toronto- Toronto.

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100-07-08 Evaluating Deductive Arguments - P&A,...

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