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Intorduction to logical fallacies

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  1. 1. Fallacies of Arguement
  2. 2. Origins of Word <ul><li>The word “fallacy” may derive from the Latin word fallere meaning, “to deceive, to trip, to lead into error or to trick.” The word may also derive from the Greek phelos, meaning “deceitful.” </li></ul>
  3. 3. About Fallacies <ul><li>Fallacies tend to exploit common psychological aspects of our mind: many people think that they are good arguments. </li></ul><ul><li>One reason why there are so many fallacies is that many people use arguments to persuade other people, and to win debates, rather than to find the truth. </li></ul><ul><li>As someone said: “Arguments are to people as what lampposts are for drunks: they are used for support rather than illumination”. </li></ul>
  4. 4. More about Fallacies <ul><li>There is probably a good evolutionary reason for why people want to persuade, rather than find the truth: it is much easier to persuade, and there are immediate pay-offs to persuading others, while finding the truth is hard, and even if you find it, there may not be an immediate pay-off. </li></ul>
  5. 5. Still More About Fallacies <ul><li>Since we are doing philosophy in this course, our goal of arguments is to find the truth, not to win or persuade. </li></ul><ul><li>Accordingly, in this course a good argument is understood as an argument that gets us closer to the truth, i.e. an argument that is sound. </li></ul>
  6. 6. Beware of the Fallacy <ul><li>Of course, lawyers, politicians, car sales people, and basically everyone else (!) defines a good argument as one that is persuasive, sound or not. </li></ul>
  7. 7. Argumentum ad Hominem (Abusive) <ul><li>Literally means against the man </li></ul><ul><li>Attacking the arguer instead of their argument. </li></ul>
  8. 8. Argumentum ad Hominem <ul><li>“ We must dismiss the conclusion of Ms. Smith’s argument because it is clear to me at this point that Ms. Smith is a liar and a thief!” </li></ul><ul><li>“ Einstein couldn't have been right about Relativity, for just look at the way he combs his hair. ” </li></ul>
  9. 9. Ad Hominem <ul><li>Billy-Bob says we should make dog fighting an Olympic sport but he’s a redneck. Therefore, we shouldn't allow it. </li></ul>
  10. 10. ad Hominem (Circumstantial) <ul><li>An attempt to refute another’s argument by attacking an the arguer’s circumstances, situation, or motives. </li></ul><ul><li>“ I believe murderers should die for the sake of the victim’s family.” </li></ul><ul><li>“ Well, since your cousin was murdered, it isn’t hard to see why you feel that way.” </li></ul>
  11. 11. ad Hominem ( Hypocrisy ) <ul><li>Person A makes claim X. </li></ul><ul><li>Person B asserts that A's actions or past claims are inconsistent with the truth of claim X. </li></ul><ul><li>Therefore X is false. </li></ul>
  12. 12. ad Hominem ( Hypocrisy ) <ul><li>Peter: &quot;Based on the arguments I have presented, it is evident that it is morally wrong to use animals for food or clothing.&quot; Bill: &quot;But you are wearing a leather jacket and you have a roast beef sandwich in your hand! How can you say that using animals for food and clothing is wrong!&quot; </li></ul>
  13. 13. Argumentum ad Baculum <ul><li>Also called an Appeal to force </li></ul><ul><li>The Latin term &quot;argumentum ad baculum&quot; literally means &quot;argument to the stick&quot; - this fallacy makes an implicit or explicit threat of physical or psychological violence against others if they refuse to accept the conclusions offered. </li></ul>
  14. 14. Argumentum ad Baculum <ul><li>Person L says accept argument A or event x will happen. </li></ul><ul><li>Event x is bad, dangerous or threatening.. </li></ul><ul><li>Therefore, argument A is a good argument. </li></ul>
  15. 15. Argumentum ad Baculum <ul><li>“ Dear Professor Duboise, when considering my grade in your class please keep in mind that my father is the Dean (your boss). </li></ul>
  16. 16. Post Hoc Ergo Propter Hoc <ul><li>Also called False Cause </li></ul><ul><li>A happened </li></ul><ul><li>B happened after A </li></ul><ul><li>Therefore, A caused B </li></ul>
  17. 17. Post Hoc Ergo Propter Hoc <ul><li>&quot;I wore my lucky shoes yesterday and didn’t drown when the boat went down. Therefore the shoes caused me not to drown. &quot; </li></ul>
  18. 18. Post Hoc Ergo Propter Hoc <ul><li>Women were allowed to vote in the early 1900’s and then we had two world wars. Clearly giving them the vote was a bad idea. </li></ul>
  19. 19. Slippery Slope ( camels nose ) <ul><li>If A is allowed to happen then X, Y and Z will also happen. </li></ul><ul><li>No proof is given as to why XYZ will happen. </li></ul>
  20. 20. Slippery Slope ( camels nose ) <ul><li>&quot;We have to stop the tuition increase! The next thing you know, they'll be charging $40,000 a semester!&quot; </li></ul><ul><li>&quot;We've got to stop them from banning pornography. Once they start banning one form of literature, they will never stop. Next thing you know, they will be burning all the books!&quot; </li></ul>
  21. 21. Hasty Generalization <ul><li>Sample S, which is too small, is taken from population P. </li></ul><ul><li>Conclusion C is drawn about Population P based on S. </li></ul>
  22. 22. Hasty Generalization <ul><li>&quot;Wow!  Did you see that teenager run that red light?  Teenage drivers are really pathetic.&quot; </li></ul><ul><li>Bob is from Callander and he is a tool. I bet the whole town is full of morons. </li></ul>
  23. 23. Ad Populum <ul><li>Most people approve of X (have favorable emotions towards X). </li></ul><ul><li>Therefore X is true. </li></ul>
  24. 24. Ad Populum <ul><li>For example, suppose that a skilled speaker managed to get most people to absolutely love the claim that 1+1=3. It would still not be rational to accept this claim simply because most people approved of it </li></ul>
  25. 25. Ad Populum <ul><li>&quot;I read the other day that most people really like the new gun control laws. I was sort of suspicious of them, but I guess if most people like them, then they must be okay.&quot; </li></ul>
  26. 26. Ad Populum
  27. 27. Fallacy Review <ul><li>Person A makes claim X. </li></ul><ul><li>Person B makes an attack on person A. </li></ul><ul><li>Therefore A's claim is false. </li></ul><ul><li>Name that fallacy </li></ul><ul><li>Ad Hominem </li></ul>
  28. 28. Fallacy Review <ul><li>&quot;You know, Professor Smith, I really need to get an A in this class. I'd like to stop by during your office hours later to discuss my grade. I'll be in your building anyway, visiting my father. He's your dean, by the way. I'll see you later.&quot; </li></ul><ul><li>Name that fallacy </li></ul><ul><li>Ad Baculum </li></ul>
  29. 29. Fallacy Review <ul><li>&quot;That was a singularly brilliant idea. I have never seen such a clear and eloquent defense of Plato's position. If you do not mind, I'll base my paper on it. Provided that you allow me a little extra time past the deadline to work on it.&quot; </li></ul><ul><li>Name that Fallacy </li></ul><ul><li>Appeal to Flattery </li></ul>
  30. 30. Fallacy Review <ul><li>Jill: &quot;He'd be a terrible coach for the team.&quot; Bill: &quot;He had his heart set on the job, and it would break if he didn't get it.&quot; Jill: &quot;I guess he'll do an adequate job.&quot; </li></ul><ul><li>Name that Fallacy </li></ul><ul><li>Appeal to Pity </li></ul>
  31. 31. Fallacy Review <ul><li>Most people approve of X (have favorable emotions towards X). </li></ul><ul><li>Therefore X is true. </li></ul><ul><li>Name that Fallacy </li></ul><ul><li>Ad Populum </li></ul>
  32. 32. Fallacy Review <ul><li>Sure I believe in God. People have believed in God for thousands of years so it seems clear that God must exist. After all, why else would the belief last so long? </li></ul><ul><li>Name that Fallacy </li></ul><ul><li>Appeal to Tradition </li></ul>
  33. 33. Fallacy Review <ul><li>Person A makes claim X. </li></ul><ul><li>Person B asserts that A makes claim X because it is in A's interest to claim X. Therefore claim X is false. </li></ul><ul><li>Name that Fallacy </li></ul><ul><li>Ad Hominem Circumstantial </li></ul>
  34. 34. Fallacy Review <ul><li>I had been doing pretty poorly this season. Then my girlfriend gave me this neon laces for my spikes and I won my next three races. Those laces must be good luck...if I keep on wearing them I can't help but win! </li></ul><ul><li>Name that Fallacy </li></ul><ul><li>False Cause or Post Hoc Ergo Propter Hoc </li></ul>
  35. 35. Fallacy Review <ul><ul><li>My opponent claims that a federally sponsored health care program will solve the health care crisis in this country. But my opponent is an East-coast liberal without a moral spine. So, my opponent is wrong: a federally sponsored health care program will not solve the health care crisis in this country. </li></ul></ul>
  36. 36. Fallacy Review <ul><li>&quot;Where did you hide the money you stole?&quot; </li></ul><ul><li>Name that Fallacy </li></ul><ul><li>Loaded Question </li></ul>
  37. 37. Fallacy Review <ul><li>&quot;Look, you are going to have to make up your mind. Either you decide that you can afford this stereo, or you decide you are going to do without music for a while.&quot; </li></ul><ul><li>False Dichotomy </li></ul>
  38. 38. Fallacy Review <ul><li>&quot;We've got to stop them from banning pornography. Once they start banning one form of literature, they will never stop. Next thing you know, they will be burning all the books!&quot; </li></ul><ul><li>Name that Fallacy </li></ul><ul><li>Slippery Slope </li></ul>
  39. 39. Fallacy Review <ul><li>Jill is horrified by the way the state uses capital punishment. Bill says that capital punishment is fine, since those the state kill don't have any qualms about killing others. </li></ul><ul><li>Name that Fallacy </li></ul><ul><li>Tuo Quo Que </li></ul>
  40. 40. New Fallacies
  41. 41. Begs the Question <ul><li>Begging the Question is a fallacy in which the premises include the claim that the conclusion is true or (directly or indirectly) assume that the conclusion is true. This sort of &quot;reasoning&quot; typically has the following form. </li></ul>
  42. 42. Begs the Question <ul><li>Premises in which the truth of the conclusion is claimed or the truth of the conclusion is assumed (either directly or indirectly). </li></ul><ul><li>Claim C (the conclusion) is true. </li></ul>
  43. 43. Begs the Question <ul><li>&quot;If such actions were not illegal, then they would not be prohibited by the law.&quot; </li></ul>
  44. 44. Begs the Question <ul><li>Bill: &quot;God must exist.&quot; Jill: &quot;How do you know.&quot; Bill: &quot;Because the Bible says so.&quot; Jill: &quot;Why should I believe the Bible?&quot; Bill: &quot;Because the Bible was written by God.&quot; </li></ul>
  45. 45. Hasty Generalization <ul><li>This fallacy is committed when a person draws a conclusion about a population based on a sample that is not large enough. It has the following form: </li></ul><ul><li>Sample S, which is too small, is taken from population P. </li></ul><ul><li>Conclusion C is drawn about Population P based on S. </li></ul>
  46. 46. Hasty Generalization <ul><li>&quot;Jim Bakker was an insincere Christian. </li></ul><ul><li>Therefore all Christians are insincere.” </li></ul><ul><li>That guy from Callander was mouth breather. </li></ul><ul><li>I bet all people from there are dumb. </li></ul>
  47. 47. Red Herring
  48. 48. Red Herring <ul><li>Topic A is under discussion. </li></ul><ul><li>Topic B is introduced under the guise of being relevant to topic A (when topic B is actually not relevant to topic A). </li></ul><ul><li>Topic A is abandoned. </li></ul>
  49. 49. Red Herring <ul><li>The premier's tax policies may be popular, but I suspect he had an affair and is paying the woman to keep quiet. The media should investigate that! </li></ul>
  50. 50. Red Herring <ul><li>Mrs.: Jones: I sure hope you aren’t considering home schooling your kids. Don’t you know home schooled kids aren’t properly socialized? </li></ul><ul><li>Mrs.: Smith: How do you know that? </li></ul><ul><li>Mrs.: Jones: Because they just aren’t. I know some home schooled kids who don’t know a thing about geography. They couldn’t even find Cache Bay on a map of Ontario. </li></ul>
  51. 51. Red Herring <ul><li>I can't believe you thought that latest Disney movie was ok for children to watch. Disney pays 12-year old girls 31 cents an hour to sow their products together </li></ul>
  52. 52. Straw Man
  53. 53. Straw Man <ul><li>The Straw Man fallacy is committed when a person simply ignores a person's actual position and substitutes a distorted, exaggerated or misrepresented version of that position. This sort of &quot;reasoning&quot; has the following pattern: </li></ul>
  54. 54. Straw Man <ul><li>Person A has position X. </li></ul><ul><li>Person B presents position Y (which is a distorted version of X). </li></ul><ul><li>Person B attacks position Y. </li></ul><ul><li>Therefore X is false/incorrect/flawed. </li></ul>
  55. 55. Straw Man <ul><li>&quot;Senator Jones says that we should not fund the attack submarine program. I disagree entirely. I can't understand why he wants to leave us defenseless like that.&quot; </li></ul>
  56. 56. Ad Ignorantium <ul><li>Argumentum ad ignorantiam means &quot;argument from ignorance.&quot; The fallacy occurs when it's argued that something must be true, simply because it hasn't been proved false. Or, equivalently, when it is argued that something must be false because it hasn't been proved true. </li></ul>
  57. 57. Ad Ignorantium <ul><li>Ad Ignorantium has two forms: </li></ul><ul><li>1. P is true, because it has not been proven false. </li></ul><ul><li>2. P is false, because it has not been proven true. </li></ul>
  58. 58. Ad Ignorantium <ul><li>No one has been able to disprove the existence of God. </li></ul><ul><li>Therefore: God exists. </li></ul>
  59. 59. Ad Ignorantium <ul><li>&quot;Of course telepathy and other psychic phenomena do not exist. </li></ul><ul><li>Nobody has shown any proof that they are real.&quot; </li></ul>
  60. 60. Argumentum Ad Nauseam <ul><li>Constant repetition of A </li></ul><ul><li>Eventually A must be held to be true </li></ul>
  61. 61. Accident <ul><li>the fallacy of applying a general rule to a particular case whose special circumstances render the rule inapplicable. </li></ul><ul><li>E.g ., &quot;Thou shalt not kill;  therefore, you should not try to control termites in your home or fight for your country.&quot; </li></ul>
  62. 62. Accident eg. <ul><li>Allowing football players to hit each other on the field is wrong as we have a school rule that states that students hitting other students is wrong. Therefore football should be banned. </li></ul>
  63. 63. Converse Accident <ul><li>This argument goes in the opposite direction of the fallacy of accident. In this case, specific situation or example is used to undermine a general rule while overlooking atypical features of the situation. </li></ul>
  64. 64. Converse Accident Eg. <ul><li>Football players are allowed to hit each other, so the school rule that prohibits students from hitting each other should be banned. </li></ul>