Critical Thinking Ch 6 Logical Fallacies II Fallacies

Critical Thinking Ch 6 Logical Fallacies II Fallacies of Insufficient Evidence 1 Lecture Notes © 2008 Mc. Graw Hill Higher Education

The Fallacies of Insufficient Evidence 1. 2. 3. 4. 5. 6. 7. 8. 9. Inappropriate Appeal to Authority Appeal to Ignorance False Alternatives Loaded Questionable Cause Hasty Generalizations Slippery Slope Weak Analogy Inconsistency 2 Lecture Notes © 2008 Mc. Graw Hill Higher Education

1 Inappropriate Appeal to Authority …citing an authority who, there is good reason to believe, is unreliable. ¢ Ways we can question reliability: ¢ Are they an authority/expert? l Are they biased? l Are they citing their source correctly? l Does the authority disagree with expert consensus? l 3 Lecture Notes © 2008 Mc. Graw Hill Higher Education

2 Appeal to Ignorance ¢ …claims that, the failure to prove something false, entails that it is true. l ¢ e. g. , There must not be intelligent life on other planets. We have never found any. Exception: l If a search is exhaustive (we looked everywhere), or extensive (we tested for years), then a lack of evidence can be sufficient evidence. 4 Lecture Notes © 2008 Mc. Graw Hill Higher Education

3 False Alternatives ¢ Insisting that there are less choices than there actually are. l ¢ e. g. , You can either study or work, but you don’t want to work, so you must study. They also can be in the form of an “if then. ” l e. g. , If we don’t get married, our lives will be worthless and we don’t want that! So we should get married. 5 Lecture Notes © 2008 Mc. Graw Hill Higher Education

4 Loaded Question Contains a presupposition such that, either way you answer it, you will appear to endorse that assumption. ¢ Examples: l Have you stopped cheating on your exams? ¢ 6 Lecture Notes © 2008 Mc. Graw Hill Higher Education

5 Questionable Cause ¢ …claims, without sufficient evidence, that one thing is the cause of something else. l The post hoc fallacy: A causes B just because A came before B. • e. g. , I’d drunk the ginseng tea and I was better by the next day. The tea must have made me better. l Correlation fallacy: the constant conjunction of A and B entails that they are causally related. • e. g. , Every time I go to the washroom, the phone rings. l Oversimplified cause fallacy: A is the cause of B when clearly B has many causes. • e. g. , Employment has been weak. Government stimulus must have Lecture Notes © 2008 Mc. Graw Hill Higher not 7 been sufficient. Education

6 Hasty Generalization ¢ ¢ …draws a general conclusion from a sample that is biased or too small. l Biased sample: I polled 1000 patrons from 100 malls, only 5% of them don’t drive. I guess most Malaysians drive. l Too small of a sample: I asked my professors if they liked MJ, and only one did. I guess professors don’t like MJ. If it doesn’t have a “general conclusion, ” then it’s not a generalization. 8 Lecture Notes © 2008 Mc. Graw Hill Higher Education

7 The Slippery Slope ¢ …claims, without sufficient evidence, that a seemingly harmless action will lead to a terrible one. l e. g. , Dr Friedman has proposed that we let AIG and GM go bankrupt. No sensible person should listen to such an proposal. If we allow AIG and GM to fall, the whole US economy will collapse. 9 Lecture Notes © 2008 Mc. Graw Hill Higher Education

8 Weak Analogy ¢ ¢ …compares two (or more) things that aren’t really comparable in the relevant respect. l e. g. , Lettuce is leafy and green and good on burgers. Poison Ivy is leafy and green. It would be good on burgers too. Exception: l e. g. Yingluck lives in a mansion and she is rich. Abhisit lives in a mansion. Abhisit is probably rich too. 10 Lecture Notes © 2008 Mc. Graw Hill Higher Education

9 Inconsistency ¢ …espouses two logically contradictory claims. l ¢ e. g. , Nobody goes there anymore; it’s too crowded. The only exception to this rule: l Laden is dead even though he isn’t. • If you mean “he’s emotionally dead, you are just being unclear (by being ambiguous). 11 Lecture Notes © 2008 Mc. Graw Hill Higher Education

Tutorial All marked ones ¢ Exercise 6. 1, Parts 1 and 2 ¢ 12 Lecture Notes © 2008 Mc. Graw Hill Higher Education