intro phil - informal fallacies (x12) (-) (1).pptx

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Informal logical fallacies William A. Bauer Bauer - Informal logical fallacies 1
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What is a logical fallacy? A fallacy is a formal or informal flaw in reasoning For instance: (P1) If the fetus is a person, abortion is wrong If A, then B (P2) The fetus is a person [has full rights] A (C) Hence, abortion is wrong Hence, B Bauer - Informal logical fallacies Yes . Convincing? No . Problem : Premise 2 is just as controversial as the conclusion and assumes what the arguer wants, thus begging the question (an informal fallacy) 2
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First category of fallacies: FORMAL A problem with the logical form of a deductive argument The problem is the form, not the content FORM EXAMPLE If A, then B If Socrates is human, Socrates is mortal. Not A Socrates is not human. Not B So, Socrates is not mortal. Bauer - Informal logical fallacies INVALID Denying the antecedent 3
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Second category of fallacies: INFORMAL Occur when the premises do not effectively support the conclusion for reasons other than form Can be due to logical or extra-logical factors (psychological, semantic, statistical) Here we cover 12 (out of 100s) of informal fallacies Bauer - Informal logical fallacies 4
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Fallacy: Ad Hominem Person X claims that p + X has some negative trait Thus, p is false (p = any statement or proposition) Ronald argues that we do not need Wall Street regulations. But this guy won’t release his own tax returns. Thus, we should keep Wall Street regulations. Truth or falsity of p has nothing to do with character, behavior, or traits of X (unless p is about X’s character, etc.) Bauer - Informal logical fallacies 5
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Fallacy: Ad Hominem Bauer - Informal logical fallacies “ad hominem”: to the man , against the man [personal attack] Variations include Insults: can you recall any recent examples in the news? tu quoque (you too), e.g., “you’re a liar too!” dismissing X’s claim that p because it is inconsistent with X’s other beliefs or practices 6
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Fallacy: Appeal to Nature Action (or event, or object) X is natural Thus, X is right (or good) Action (or event, or object) X is not natural Thus, X is wrong (or bad) Just because X is natural (or unnatural) does not entail that it is good (or bad) Bauer - Informal logical fallacies Form 1 Form 2 7
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Fallacy: Appeal to Nature Herbal Cure is an all-natural pain reliever Thus, you should use Herbal Cure Many alternative medicines are no better than a placebo Some natural things are very bad, some unnatural things are very good Bauer - Informal logical fallacies 8
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Fallacy: Appeal to Nature Homosexual acts are unnatural Thus, homosexual acts are wrong Assuming for the sake of argument that homosexual acts are considered “unnatural” this alone does not establish the wrongness of such acts Also, what makes an action ‘unnatural’?
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  • Fall '16
  • Jon Newton
  • Logic, William A. Bauer

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