Logical Fallacies. Introduction and Activities

Transcription

1 Logical Fallacies Introduction and Activities

2 What is a logical fallacy? A fallacy is an error of reasoning. These are flawed statements that often sound true 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.

3 Why study logical fallacies? It is important to develop logical fallacy detection skills in your own writing, as well as others. Think of this as intellectual kung-fu: the art of intellectual self defense. (Logical Fallacies Handlist)

4 Post hoc ergo propter hoc(non sequitur ) Assuming one thing causes another just because one follows another. As the number of churches in the USA increases, so do the number of prostitutes Crime is increasing in Germany, but so is the number of college graduates. So education is corrupting the young The homeless man was seen in front of the shop before it was robbed, so he did it

5 Ad hominem Attacking the person you disagree with instead of their argument As Hitler's interest in art attests, the love of art is a dangerous antecedent to fascism You may argue that God doesn t exist, but that s just because you are so bigoted. You claim that Tim is innocent, but why should we listen to you? You are criminal too Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Press

6 Equivocation This fallacy uses a word/idea with two different meanings in two different ways to support an argument Fries and a coke are better than nothing, and nothing is better than good health, so fries and coke are better than good health Scientists say that red wine can prevent heart disease. I drink a bottle every night, so I must have a really healthy heart.

7 Ad ignorantiam Claiming that something is true because it cannot be proved to be false. Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Press

8 You cannot explain where God is, so God doesn t exist Scientist have not proven that global warming will occur, so let s not worry about it

9 False dilemma This fallacy presents a limited choice as the only possible options when there may be many other choices/conclusions. Assuming that only a limited number of alternatives exist. Binary thinking-black/white thinking.

10 If you don t let me go to this party, I ll be a total loser at school If you are against the war in Iraq, then you must hate America. Either we cut welfare benefits or we raise income tax : that is the choice we face

11 Loaded question A question that is biased because it contains a built-in assumption. Do you always cheat on exams? Did you beat your students today? Why do you hate America and freedom so much? Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

12 Hasty generalisation Generalising from insufficient evidence. Fred the Australian stole my wallet. All Australian are thieves. Six of my friends like the new school uniform-it will be really popular All the new - born babies I ve seen are so cute! Our child is going to be absolutely adorable!

13 Special pleading Using double standards to excuse an individual or group. The law requires everyone to follow the speed limit and other traffic regulations, but in Mumbai, exceptions should be made for cops and their families, police union officials say. I know there is a drought and we need to save water, but I am putting my prize flowers in a competition next week and I need to given them plenty of water Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Press

14 False analogy Assuming that because two things are alike in one way that they are alike in other respects. Just as in time the gentle rain can wear down the tallest mountains, so in human life, all problems can be solved by patience and quiet persistence Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Press

15 Circular reasoning Assuming the truth of what you are supposed to be proving. Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Press

16 The soldier gave out the guns, but kept an extra one for himself. When asked why, he said I am the leader. Why are you the leader? Because I have more guns I know my president is a good man, because he says he is and a good man would not lie I know I am smarter than you, because it would be foolish to say so if it wasn t true, and I am not a fool.

17 Circular reasoning is the best fallacy and is capable of proving anything. Since it can prove anything, it can obviously prove the above statement. Since it can prove the first statement, it must be true. Therefore, circular reasoning is the best fallacy and is capable of proving anything.

18 In each of the following cases, decide which best applies to the argument. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question.

19 1. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. Since strict gun control laws were introduced in Dodge City, the crime rate has risen. This shows that gun control does nothing to reduce crime. Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

20 post hoc ergo propter hoc Since strict gun control laws were introduced in Dodge City, the crime rate has risen. This shows that gun control does nothing to reduce crime.

21 2. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. Emmeline said she trusted me, and she must be telling the truth because she wouldn t lie to someone that she trusted. Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

22 circular reasoning Emmeline said she trusted me, and she must be telling the truth because she wouldn t lie to someone that she trusted. Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

23 3. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. The ends justifies the means. After all, if you want to make omelettes, you have to break eggs. Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

24 false analogy The ends justifies the means. After all, if you want to make omelettes, you have to break eggs.

25 4. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. That can t be right, non of my friends would believe it. Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

26 ad hominem That can t be right, non of my friends would believe it.

27 5. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. Since many great scientists have believed in God, there must be some truth in religion. Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

28 ad hominem Since many great scientists have believed in God, there must be some truth in religion.

29 6. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. Teddy and Seanne got on very well on their two dates together. They are clearly well suited and should get married. Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

30 hasty generalisation Teddy and Seanne got on very well on their two dates together. They are clearly well suited and should get married.

31 7. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. Do you want to be part of the solution, or part of the problem? Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

32 false dilemma Do you want to be part of the solution, or part of the problem?

33 8. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. I agree that you shouldn t copy mp3s illegally, but I ve only copied a few and I do buy tracks sometimes. Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

34 special pleading I agree that you shouldn t copy mp3s illegally, but I ve only copied a few and I do buy tracks sometimes.

35 9. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. The average UK family has 2.5 children. The Smiths are average people, they must have 2.5 kids. Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

36 equivocation The average UK family has 2.5 children. The Smiths are average people, they must have 2.5 kids.

37 10. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. Since no-one has been able to prove that God didn t create the universe, we must conclude that God did make everything. Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

38 ad ignorantium Since no-one has been able to prove that God didn t create the universe, we must conclude that God did make everything.

39 11. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. Are all your family stupid, or is it just you? Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

40 loaded question Are all your family stupid, or is it just you?

41 12. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. No scandal has ever touched Mr Porter. He must be a clean living and honest man. Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

42 ad ignorantium No scandal has ever touched Mr Porter. He must be a clean living and honest man.

43 13. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. Just as you are more likely to take care of a car that you own rather than a car that you rent, a slave owner would look after a slave better than an employer would look after their worker. Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

44 false analogy Just as you are more likely to take care of a car that you own rather than a car that you rent, a slave owner would look after a slave better than an employer would look after their worker.

45 14. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. To ignore the possibility that Norway landed the first person on the moon just because nobody has heard of a Norwegian space program is arrogant. If we are unaware of something does not mean that it never happened. Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

46 ad ignorantium To ignore the possibility that Norway landed the first person on the moon just because nobody has heard of a Norwegian space program is arrogant. If we are unaware of something does not mean that it never happened.

47 15. Hasty generalisation, post hoc ergo propter hoc, circular reasoning, ad hominem, special pleading, ad ignorantium, false dilemma, false analogy, equivocation, loaded question. In the fight against terrorism, you are either with the USA or against. Theory of Knowledge for the IB Diploma, Richard van de Lagemaat, Cambridge University Pres

48 false dilemma In the fight against terrorism, you are either with the USA or against.

49 Activity - sell a product Work on group using as many fallacies as you can go overboard to make the fallacies as outrageous as possible. After each group presents, the other class members should try to identify the fallacies. Cleaning products or products that invoke ideals (like patriotism, environmentalism, corruption) work particularly well for this activity.

50 Causes of bad reasoning Rationalisation Manufacturing arguments to justify our ignorance, pride, laziness and prejudices Take any editorial or opinion article from a newspaper and see how many logical fallacies you can find in it. Have you ever rationalized?