PHIL 110 Lecture Notes - Lecture 8: Modus Ponens, First-Order Logic, Modus Tollens
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16 Mar 2017
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Dr mc"s philosophy 110 (1171) part notes 5#1 . Avoids having to do the whole truth table. Assign t to all the premises and f to the conclusion, and see if you can assign truth values to the atomic components in keeping with that. Problem: it can be difficult to tell whether you cannot, or it just did not. Full truth tables are better for establishing validity. Find an interpretation in which they are all true. B a, c b, ~c a. If the premises of an argument are inconsistent, the argument is valid. If it is consistent, we can check the counterexample set for consistency. If it is consistent, the argument is invalid. Some have said it really does reflect ordinary english: If hitler was a good guy, then i"m a monkey"s uncle. The idea is that the speaker is asserting a true sentence, but the antecedent and consequent are both false.