Rationality and Truth


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1 THE UNIVERSITY OF BRITISH COLUMBIA Philosophy 1101 – Introduction to Philosophy Richard Johns September 2010 Logic, Rationality and Truth 1. Logical Arguments In this week’s reading from the textbook, we read W. K. Clifford’s view that beliefs must be supported by evidence. But if the belief has been accepted on insufficient evidence, the pleasure is a stolen one. Not only does it deceive us by giving us a sense of power which we do not really possess, but it is sinful, because it is stolen in defiance of our duty to mankind. The duty is to guard ourselves from such beliefs as from a pestilence … (in Pojman, p. 262.) In the language used by logicians, we say that conclusions must be supported by premises. Philosophers (in the analytic tradition), like W. K. Clifford, place a very high value on logical arguments as a means to discover truth. Consider, for example, the claim that s sometimes made, that “Heterosexual men are more promiscuous than heterosexual women.” According to do one survey, for example, Men average 7 sexual partners per lifetime, and women only 4. The claim above has been questioned on purely logical grounds, using the following argument that attempts to establish a contrary conclusion. Premise . The number of (heterosexual) men equals the number of (heterosexual) women (at least approximately). The average number of sexual relationships for men in the population is by definition S divided by N , where S is the sum of all the numbers of such relationships for individual men, and N the number of men. It is clear however that S also equals the number of distinct (hetero)sexual relationships in the population, for each sexual partner that each man has defines a unique sexual relationship, consisting of one man and one woman. Further, the total number of (hetero)sexual relationships involving females also takes this value S . Then, since the number of women is also N , the average number of sexual partners per woman is S / N . Conclusion . (Heterosexual) Women are, on average, exactly as promiscuous as heterosexual men.
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2 The paragraph of text between the premise and conclusion contains reasoning . The author’s intent is that the reader be led to “see” that the conclusion is true, just as long as the premise is, or that the conclusion “follows from” the premise. Does the reasoning above convince you? Are you persuaded that (heterosexual) men and women are equally promiscuous? If you are properly convinced, then the argument is said to be deductively valid. The word “properly” is needed in the previous sentence, since people are sometimes convinced by flimsy reasoning. Consider the following. Premises . 1. Almost all philosophy professors are men. 2. The vast majority of men drink beer
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This note was uploaded on 11/30/2010 for the course PHIL 1101 taught by Professor Johns during the Fall '10 term at Langara.

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