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phil001notesWeek5 - Dr Mcs Philosophy 001(1091 Lecture...

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1091001notesWeek5 © 1 Dr Mc’s Philosophy 001 (1091) Lecture Notes, Week 5 © If you know that an argument is valid, should you accept its conclusion? Leibniz’s argument: 1. If (a Judeo-Christian) God exists, then this is the best of all possible worlds. 2. (A Judeo-Christian) God exists. 3. This is the best of all possible worlds. Voltaire’s argument: 1. If (a Judeo-Christian) God exists, then this is the best of all possible worlds. 2. This is not the best of all possible worlds. 3. (A Judeo-Christian) God does not exist. Two valid arguments, but it would not be rational to accept them both. The conclusion of one is in conflict with a premise of the other. It is not rational to accept both at the same time. Soundness and Strength We must deal with deductive and inductive arguments separately. I. Deductive soundness and strength An argument is deductively sound if and only if (i) it is valid, and (ii) all its premises are true. Examples? Valid arguments whose premises correspond to the facts. 1. If Dr Mc is tall er than 12 feet, then she’s taller than 10 feet. 2. Dr Mc is not taller than 10 feet. 3. Dr Mc is not taller than 12 feet. D4.1 . An argument is deductively strong for a person if and only if i) it is deductively valid, and ii) it is reasonable for the person to beli eve all the argument’s premises. Examples of strong arguments depend upon the person in question. The above argument is (I hope!) strong for all of us. I.e., it is reasonable for all of us to think it is sound. 1. If there are exactly 13 people in this room now, everybody in 001 this term will get an A. 2. There are exactly 13 people in this room now. 3. Everybody in 001 this term will get an A. This is valid. Is it a deductively strong argument for you?
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