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Logical Fallacies
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Logical Fallacies

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Logical fallacies lecture

Logical fallacies lecture

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  • 1. logical fallacieslogical fallacies THE ART OF DEBATETHE ART OF DEBATE From OWL English PurdueFrom OWL English Purdue
  • 2. What is a logicalWhat is a logical fallacy?fallacy? Fallacies are common errors in reasoning that willFallacies are common errors in reasoning that will undermine the logic of your argument.undermine the logic of your argument. Fallacies can be either illegitimate arguments orFallacies can be either illegitimate arguments or irrelevant pointsirrelevant points They are often identified because they lack evidence thatThey are often identified because they lack evidence that supports their claim.supports their claim. Avoid these fallaciesAvoid these fallacies
  • 3. Types of LogicalTypes of Logical FallaciesFallacies SLIPPERY SLOPESLIPPERY SLOPE HASTY GENERALIZATIONHASTY GENERALIZATION POST HOC ERGO PROPTER HOCPOST HOC ERGO PROPTER HOC GENERIC FALLACYGENERIC FALLACY BEGGING THE CLAIMBEGGING THE CLAIM CIRCULAR ARGUMENTCIRCULAR ARGUMENT EITHER/ OREITHER/ OR AD HOMINEMAD HOMINEM AD POPULUMAD POPULUM RED HERRINGRED HERRING STRAW MANSTRAW MAN
  • 4. Slippery SlopeSlippery Slope This is a conclusion based on the premise that isThis is a conclusion based on the premise that is AA happens, then eventually through a series of small steps,happens, then eventually through a series of small steps, throughthrough BB,, CC, ...., ....XX,, YY,, ZZ will happen, too, basicallywill happen, too, basically equatingequating AA andand ZZ. So , if we don’t want. So , if we don’t want ZZ to occur,to occur, AA must not be allowed to occur either.must not be allowed to occur either.
  • 5. Slippery SlopeSlippery Slope This is a conclusion based on the premise that isThis is a conclusion based on the premise that is AA happens, then eventuallyhappens, then eventually through a series of small steps, throughthrough a series of small steps, through BB,, CC, ...., ....XX,, YY,, ZZ will happen, too, basicallywill happen, too, basically equatingequating AA andand ZZ. So , if we don’t want. So , if we don’t want ZZ to occur,to occur, AA must not be allowed to occurmust not be allowed to occur either.either. Example:Example: If we ban Hummers because they are badIf we ban Hummers because they are bad for the environment, eventually the government will banfor the environment, eventually the government will ban all cars, so we should not ban Hummers.all cars, so we should not ban Hummers. In this example the author is equating banningIn this example the author is equating banning Hummers with banning all cars, which is not the sameHummers with banning all cars, which is not the same thing.thing.
  • 6. Hasty GeneralizationHasty Generalization This is conclusion based on insufficient or biasedThis is conclusion based on insufficient or biased evidence.evidence. In other words, you are rushing to a conclusion beforeIn other words, you are rushing to a conclusion before you have all the relevant facts.you have all the relevant facts.
  • 7. Hasty GeneralizationHasty Generalization This is conclusion based on insufficient or biasedThis is conclusion based on insufficient or biased evidence.evidence. In other words, you are rushing to a conclusion beforeIn other words, you are rushing to a conclusion before you have all the relevant facts.you have all the relevant facts. Example:Example: Even though it’s only the first day, I canEven though it’s only the first day, I can tell this is going to be a boring course.tell this is going to be a boring course. Write your own fallacy.Write your own fallacy.
  • 8. post hoc ergo propter hocpost hoc ergo propter hoc This is the conclusion that assumes that ifThis is the conclusion that assumes that if AA occurredoccurred afterafter BB thenthen BB must have causedmust have caused AA
  • 9. post hoc ergo propter hocpost hoc ergo propter hoc This is the conclusion that assumes that ifThis is the conclusion that assumes that if AA occurredoccurred afterafter BB thenthen BB must have causedmust have caused AA ExampleExample: I drank bottled water and now I am sick,: I drank bottled water and now I am sick, so the water must have made me sick.so the water must have made me sick. In this example the author assumes that if one eventIn this example the author assumes that if one event chronologically follows another the first event mustchronologically follows another the first event must have caused the second.have caused the second. Write your own fallacy.Write your own fallacy.
  • 10. generic fallacygeneric fallacy A conclusion is based on an argument that the originsA conclusion is based on an argument that the origins of a person, idea, institution, or theory determine itsof a person, idea, institution, or theory determine its character, nature or worth.character, nature or worth.
  • 11. generic fallacygeneric fallacy A conclusion is based on an argument that the originsA conclusion is based on an argument that the origins of a person, idea, institution, or theory determine itsof a person, idea, institution, or theory determine its character, nature or worth.character, nature or worth. Example:Example: The Volkswagen Beetle is an evil carThe Volkswagen Beetle is an evil car because it was originally designed by Hitler’s army.because it was originally designed by Hitler’s army. Write your own fallacy.Write your own fallacy.
  • 12. Begging the claimBegging the claim The conclusion that the writer should prove isThe conclusion that the writer should prove is validated within the claimvalidated within the claim
  • 13. Begging the claimBegging the claim The conclusion that the writer’s proof is validatedThe conclusion that the writer’s proof is validated within the claimwithin the claim Example:Example: Filthy and polluting coal should beFilthy and polluting coal should be banned.banned. Write your own fallacy.Write your own fallacy.
  • 14. Circular argumentCircular argument This restates the argument rather than actuallyThis restates the argument rather than actually proving it.proving it.
  • 15. Circular argumentCircular argument This restates the argument rather than actuallyThis restates the argument rather than actually proving it.proving it. Example:Example: George Bush is a good communicatorGeorge Bush is a good communicator because he speaks effectively.because he speaks effectively. Write your own fallacy.Write your own fallacy.
  • 16. Either/orEither/or This is a conclusion that oversimplifies the argument byThis is a conclusion that oversimplifies the argument by reducing it to only two sides or choices.reducing it to only two sides or choices.
  • 17. Either/orEither/or This is a conclusion that oversimplifies the argument byThis is a conclusion that oversimplifies the argument by reducing it to only two sides or choices.reducing it to only two sides or choices. Example:Example: We can either stop using cars or destroyWe can either stop using cars or destroy the earth.the earth. Write your own fallacy.Write your own fallacy.
  • 18. Ad HominemAd Hominem This is an attack on the character of a person ratherThis is an attack on the character of a person rather than their opinions or argumentsthan their opinions or arguments
  • 19. Ad HominemAd Hominem This is an attack on the character of a person ratherThis is an attack on the character of a person rather than their opinions or argumentsthan their opinions or arguments Example:Example: Green Peace’s strategies aren’t effectiveGreen Peace’s strategies aren’t effective because they are all dirty, lazy hippies.because they are all dirty, lazy hippies. Write your own fallacy.Write your own fallacy.
  • 20. Ad PopulumAd Populum This is an emotional appeal that speaks to positive (suchThis is an emotional appeal that speaks to positive (such as patriotism, religion, democracy) or negative (such asas patriotism, religion, democracy) or negative (such as terrorism or fascism) concepts rather than the realterrorism or fascism) concepts rather than the real issue at handissue at hand
  • 21. Ad PopulumAd Populum This is an emotional appeal that speaks to positive (suchThis is an emotional appeal that speaks to positive (such as patriotism, religion, democracy) or negative (such asas patriotism, religion, democracy) or negative (such as terrorism or fascism) concepts rather than the realterrorism or fascism) concepts rather than the real issue at handissue at hand Example:Example: If you were a true American you wouldIf you were a true American you would support the rights of people to choose whatever vehiclesupport the rights of people to choose whatever vehicle they want.they want. Write your own fallacy.Write your own fallacy.
  • 22. Red HerringRed Herring This is a diversionary tactic that avoids the key issues,This is a diversionary tactic that avoids the key issues, often by avoiding opposing arguments rather thanoften by avoiding opposing arguments rather than addressing them.addressing them.
  • 23. Red HerringRed Herring This is a diversionary tactic that avoids the key issues,This is a diversionary tactic that avoids the key issues, often by avoiding opposing arguments rather thanoften by avoiding opposing arguments rather than addressing them.addressing them. Example:Example: The level of mercury in seafood may beThe level of mercury in seafood may be unsafe, but what will fishers do to support theirunsafe, but what will fishers do to support their families?families? Write your own fallacy.Write your own fallacy.
  • 24. Straw manStraw man This move oversimplifies an opponent’s viewpoint andThis move oversimplifies an opponent’s viewpoint and then attacks that hollow argument.then attacks that hollow argument.
  • 25. Straw manStraw man This move oversimplifies an opponent’s viewpoint and then attacksThis move oversimplifies an opponent’s viewpoint and then attacks that hollow argument.that hollow argument. People who don’t support the proposed state minimum wagePeople who don’t support the proposed state minimum wage increase hate the poor.increase hate the poor. Write your own fallacy.Write your own fallacy.
  • 26. Moral EquivalenceMoral Equivalence This fallacy compares minor misdeeds with majorThis fallacy compares minor misdeeds with major atrocities.atrocities.
  • 27. Moral EquivalenceMoral Equivalence This fallacy compares minor misdeeds with majorThis fallacy compares minor misdeeds with major atrocities.atrocities. Example:Example: That parking attendant who gave me aThat parking attendant who gave me a ticket is as bad as Hitler.ticket is as bad as Hitler.
  • 28. Moral EquivalenceMoral Equivalence This fallacy compares minor misdeeds with majorThis fallacy compares minor misdeeds with major atrocities.atrocities. Example:Example: That parking attendant who gave me aThat parking attendant who gave me a ticket is as bad as Hitler.ticket is as bad as Hitler. Write your own fallacy.Write your own fallacy.