hw3s - Homework#3 Solutions Philosophy 12A March 8 2010...

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Unformatted text preview: Homework #3 Solutions Philosophy 12A March 8, 2010 Part One 1. A → C B → C A ∨ B ∴ C is a valid argument. There are no rows in which all of its premises are true and its conclusion is false: A B C A → C B → C A ∨ B C > > > > > > > > > ⊥ ⊥ ⊥ > ⊥ > ⊥ > > > > > > ⊥ ⊥ ⊥ > > ⊥ ⊥ > > > > > > ⊥ > ⊥ > ⊥ > ⊥ ⊥ ⊥ > > > ⊥ > ⊥ ⊥ ⊥ > > ⊥ ⊥ 2. I → N ( ∼ K ∨ D) ↔ N D → ∼ I ∴ ∼ I → (N → K) is an in valid argument. Here’s a row that makes all its premises true and its conclusion false: D I K N I → N ( ∼ K ∨ D) ↔ N D → ∼ I ∼ I → (N → K) > ⊥ ⊥ > > > > ⊥ 3. ( ∼ O → ∼ S) & (O → (M & ∼ I)) ∼ I → ∼ M ∴ ∼ S is a valid argument. For the conclusion ‘ ∼ S ’ to be false, we require ‘ S ’ to be true. Now, for the first premise of this argument to be true, its first conjunct ‘ ∼ O → ∼ S ’ must be true. Hence, the antecedent ‘ ∼ O ’ of this first conjunct must be false (since its consequent ‘...
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This note was uploaded on 04/22/2010 for the course PHIL 63170 taught by Professor Fitelson during the Spring '10 term at Berkeley.

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