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Logical fallacies

Logical fallacies. Problems with premises Premise is false Premise is an unwarranted assumption Hidden premise. Attacking the person UFO sighters are crazy Members of the government must be lying because they are corrupt Name calling in itself is not a logical fallacy

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Logical fallacies

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  1. Logical fallacies

  2. Problems with premises • Premise is false • Premise is an unwarranted assumption • Hidden premise

  3. Attacking the person • UFO sighters are crazy • Members of the government must be lying because they are corrupt • Name calling in itself is not a logical fallacy • “poisoning the well” • His argument is just like Hitler’s position Ad hominem

  4. Claim held by individual is true because that person speaks from authority • Airline pilots • Judges • Professors • Popular belief • Antiquity • Similar to ‘appeal to nature’ – because something is natural it is justified Appeal to authority

  5. Assuming that the conclusion is true in one of the premises • Example: • “How long has it been since you stopped beating your wife?” • Similar to tautology • Circular reasoning – conclusion is also the premise Begging the question

  6. Adding a ‘premise’ in order to distract the opponent from the real argument Red herring

  7. Assuming that two events are linked by cause when they may be just coincidental • Correlation in a controlled experiment, though, may suggest causation • Similar to post-hoc ergo propter hoc • “After this, therefore because of this” False cause

  8. Assuming that two events / ideas are similar when they have some important difference • Similar to composition / division • What’s true about one part of something has to be true for all False analogy

  9. “doesn’t follow” • No logical connection exists Non-sequitur

  10. Assuming that, if you accept one premise, you also have to accept more extreme cases • “if A happens, then Z will happen too. Therefore, A shouldn’t happen” Slippery slope

  11. “either-or”, false dichotomy • Falsely assumes that there are only two alternatives Black-or-white

  12. Adding new premises to respond to critics and strengthen the argument • Changing the rules of the game as you go • Similar to “moving goalpost” • Changing the criteria for a good argument if the opponent comes up with evidence • Called ad-hoc reasoning Special pleading

  13. Making the opponent’s argument into a position that is easier to attack Straw Man

  14. Basing a conclusion on insufficient or biased evidence Hasty generalization

  15. “you too” • Responding to criticism by attacking the critic • Similar to ad hominem Tuquoque

  16. Ad populum • Appeal to positive emotions (e.g. patriotism) • Appeal to negative emotions (e.g. fear) • May include slippery slope, irrelevant thesis, etc. Appeal to emotion

  17. http://atheistuniverse.net/photo/thou-shalt-not-commit-logical-fallacieshttp://atheistuniverse.net/photo/thou-shalt-not-commit-logical-fallacies • http://www.theskepticsguide.org/resources/logicalfallacies.aspx • http://owl.english.purdue.edu/owl/resource/659/03/

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