Presentation is loading. Please wait.

Presentation is loading. Please wait.

Logical fallacies.

Similar presentations

Presentation on theme: "Logical fallacies."— Presentation transcript:

1 Logical fallacies


3 Two Types: Formal - a defect in the form or structure of an argument
Informal - a defect in the content, material, or the language of the argument

4 An argument is like a building.

5 Just as a building has a structure and is made out of material, so too does an argument have a structure and is made out of material.

6 The material of an argument is the language.

7 Our focus is on informal fallacies.

8 Such fallacies are committed with the intent to deceive
Such fallacies are committed with the intent to deceive. Keep in mind that the person best able to deceive you - to make his or her argument appear good - is the person who knows these fallacies. Also keep in mind that though the argument may appear to be good, it is not in fact a good argument but a fallacious one.

9 There are four basic categories of informal fallacies:
Fallacies of Relevance Fallacies of Presumption Fallacies of Ambiguity Fallacies in Ordinary Language

10 These are the fallacies we will be covering:
Fallacies of Relevance: Appeal to force Physical Psychological Appeal to pity Appeal to the People Bandwagon Vanity Snobbery

11 Fallacies of Relevance, cont.
Ad hominem Abusive Guilt by Association Tu Quoque Appeal to Tradition Misplaced Authority

12 Fallacies of Relevance, cont.
Hasty Generalization Biased Sample Unknowable statistic False cause Non sequitor Black or White

13 Fallacies of Presumption
Begging the Question Circular Reasoning Suppressed Evidence

14 Fallacies of Ambiguity
Equivocation Amphiboly

15 Fallacies in Ordinary Language
False Analogy Slippery Slope Straw Man Red Herring

16 That’s A Lot of Fallacies!!!!!!!!!

17 So on your next test, you will have to know, what?
A Lot of Fallacies!!!!!!

18 Fallacies of Relevance
Fallacies of this type have one or both of the following characteristics: the premises are logically irrelevant to the conclusion the connection between the premises and the conclusion is often emotional rather than reasonable

19 Appeal to Force Using the threat of physical or psychological force to make your opponent concede to your position.

20 There are two types of Appeal to Force

21 Appeal to Physical Force
Use the threat of physical harm to make your opponent concede to your position. This threat can be either against their person or their property.


23 Examples Agree with me or I will punch you in the nose. Now don’t you see why you should agree with me? Mrs.Lodato, I think that I should receive an ‘A’ in this class. I know you will agree. By the way, I know where you live.

24 Appeal to Psychological Force
Use the threat of psychological damage to your opponent to get them to concede to your position.

25 Examples If you do not support your local charity you will burn in hell. Therefore, you should support it. Mrs. Lodato, I think I should receive an ‘A’ in this course. I know you will agree. By the way, my father is on the Board of Directors of this college, and he does everything I tell him to do.

26 Appeal to Pity Here you appeal to your opponent’s sympathy to make them concede to your position. That is, you attempt to make your opponent believe that you will be miserable unless they concede to your position.

27 Examples Student to teacher: You should let me take the exam over, because if I do not pass this course, my mother will never forgive herself, my father will not speak to me, and even the dog will hate me. Lawyer to jury: Please let my client go. Sure he committed the murders, but it wasn’t his fault. He had a bad childhood. His mother left him when he was 18 and someone stole his puppy when he was 19.

28 Appeal to the People This fallacy uses our desires of wanting to be loved, admired, esteemed, valued, recognized, and accepted by others to make us concede to a point or accept a conclusion.

29 There are various types of appeals to the people.

30 Bandwagon Here you argue that since everyone is doing something, your opponent should do it too, otherwise he or she will be left out and not fit in with the crowd.

31 Examples Everyone enjoys smoking Whiz, so you should too
Don’t be left out in the cold. Come on in and have a Schlitz!!!!

32 Appeal to Vanity Here someone tells you that if you use a certain product or accept a certain point, you will be admired and sought after like a celebrity who is said to use the product.


34 Examples Liz Taylor uses Passion perfume, and young, naked men are after her. If you use Passion, young and naked men will be after you. Michael Jordan wears Nikke basketball shoes. If you wear them, you will play like Michael!!!!

35 Appeal to Snobbery This fallacy tells you that if you use a certain product or concede to a certain point, that you are better than everyone else, a member of the select few, and a rare individual.

36 Examples Advertisement: “Pass the jelly” Grey Poupon
Pierre Cardin luggage - the luggage that quality people buy

37 Ad Hominem Here you attack the opponent rather than the opponent’s argument.

38 There are various types of Ad Hominem

39 Abusive Here you specifically attack the person under question by calling him or her a name

40 Examples You should not vote for Al Gore because he is a ‘liberal’ and will be after your wallet. You can’t trust Joe because he has shifty eyes Why should we believe you? You have a beard, you smoke cigarettes, and you do not have a job.


42 Guilt by Association Here you unfairly judge a person or his position because of the company they keep, or because he was associated with a negative past event.

43 Examples He must be guilty, because three of his friends are in jail.
You should not re-elect Kennedy. Wasn’t his nephew convicted of murder? Don’t date Harriet. I dated her cousin and all she was after was my money.

44 Tu Quoque ‘You Too’ ‘Two Wrongs Make A Right”
This fallacy is committed when a speaker, trying to show that he is not at fault, argues that his opponent has said or done things just as bad as he, the speaker, has been accused of.

45 Examples Son to father: Sure I smoke dope dad, but you drink and that is just as bad. Daughter of mother: I should be allowed to date at age 12. You got married when you were 16. Politician: Sure I have made mistakes, but candidate X has admitted to committing adultery.

46 Misplaced Authority This fallacy is committed when testimony from an authority is used as evidence in an argument, but the authority quoted is not an authority in the field under discussion.

47 Examples Wear Leggs pantyhose. Joe Namath says they are comfortable
Psychologist to jury: The defendant does not suffer from schizophrenia. I ought to know, I have a Masters degree in Grief Therapy. Our foreign policy needs revision. Just look at the experts who support my view: Miss Piggy, fifteen logic professors, and five taxi cab drivers.

48 Appeal to Tradition This fallacy is committed when it is argued that because something was done a certain way in the past, it should continue to be done that way.

49 Examples Women should not work outside the home. My mother did not work, my grandma did not work, and neither will you. What do you mean I need to change my History text? I have been using this text for the past 50 years and I will continue to use it. Who cares if it is out of print?

50 Hasty Generalization This fallacy is committed when the reasoner ‘rushes to judgment’ or a conclusion based on too little evidence.

51 Examples The first two apples I took out of that barrel had holes in them, so probably all of the apples in that barrel have holes in them. He must be poor. He has a beard and is wearing dirty clothes. We should give him some money.

52 Biased Sample This fallacy is committed when the sample used as evidence in an argument is not representative of opinions being generalized about.

53 Examples 100% of the people surveyed believe that drunker driving laws are too strict. (note: the survey was taken outside of liquor stores and bars) 100% of the people surveyed believe that abortion is wrong. (note: the survey was given to people on their way out of church on Sunday morning)

54 Unknowable Statistic This fallacy is committed when you cite as evidence statistics that simply cannot be known by anyone.

55 Examples The majority of people, although they will never admit it, believe that abortion is wrong. 80% of people world-wide believe that there are aliens from other planets among us.

56 False Cause Post Hoc, ergo Propter Hoc
This fallacy is committed when you assert that because two events occur one after the other, that the first is the cause of the second.

57 Examples Lightning flashed and then the lights went out. The lightning caused the lights to go out. You went in Harriet’s hospital room and then she died. You killed her.

58 Non Sequitor This fallacy occurs when the premises of an argument are entirely irrelevant to the conclusion drawn.

59 Examples Plato wrote in dialogue form and it is difficult to separate his views from those of his opponents. So he is a lousy philosopher. You did not do your homework today, so you must be a rotten husband to your wife.

60 Black or White This fallacy is committed when you argue that since you opponent doesn’t agree with your position, then he must agree with the extreme of your position. You try to make you opponent or audience think that there are only two choices (yours and the extreme), when in fact there are many.

61 Examples So you don’t think that prisoners should be allowed to watch cable. Well, you would have them all in isolation, and eating nothing but bread and water. You don’t believe in buying diamonds for Valentine’s Day? Well, you must think that all women are just here to serve and slave for you.

62 Fallacies of Presumption

63 Fallacies of Presumption
These fallacies occur when the arguments presume - in some way - what they are trying to prove, or they presume evidence of some type.

64 There are Many Types of Fallacies of Presumption

65 Begging the Question This fallacy occurs when the arguer presents evidence for the conclusion as true, but the evidence presented is either an opinion or the arguer offers no proof that the evidence is in fact true.

66 Examples To be a good president, it is necessary to have at least 30 years of political experience. Jesse Jackson has not had that much political experience, so he would not make a good president. To be a good student, you must study at least four hours per night, per subject. Harry works all night and does not have time to study that long. He will fail.

67 Circular Reasoning This fallacy is committed when the argument fails to prove anything because it takes for granted what it is supposed to prove.

68 Examples Beautiful women are the best type to date because they are beautiful and fun to date. Candidate X must not be trusted because he is deceptive. Abortion is wrong because it is immoral. Smoking marijuana is wrong because taking drugs is wrong.

69 Suppressed Evidence This fallacy is committed when relevant evidence is purposely omitted in the argument because it is contrary to what the author is trying to prove.

70 Examples R.J. Reynolds Tobacco Company memos
“Jesse Jackson will not make an effective president because he has never held political office.” Here, the arguer fails to make note of the fact that Jackson does have experience in foreign policy, and he also fails to note that there have been other presidents who never held political office before becoming president.

71 Fallacies of Ambiguity
These fallacies occur when one word in an argument may be taken to have two or more distinct meanings.

72 Equivocation This fallacy occurs when the same word is used in two different senses in an argument.

73 Examples Every mystery is a religious belief and the whereabouts of the killer is a mystery. Therefore, the whereabouts of the killer is a religious belief. Computers get viruses and you have a virus so you must be a computer.

74 Amphiboly This fallacy occurs when the grammar of a statement is ambiguous and allows for more than one interpretation.

75 Examples Save trash and waste paper
Rummage sale ad: “The ladies will have cast off clothing in the church basement.”

76 Fallacies in Ordinary Language

77 False Analogy This fallacy is committed when you compare two items, and argue that because they have some characteristics in common, they must have another characteristic in common. However, you ignore or fail to point out relevant dissimilarities.

78 Examples A computer has a memory, can make predictions and can store information. The human mind also does these things. The human mind also dreams, so computers can dream as well. Note: Here the arguer fails to take into consideration relevant differences between the human mind and a computer.

79 Slippery Slope Here it is argued that if one event is allowed to occur, then a whole series of consequences will also occur. Or if you accept one point, then you must accept a series of other points. The consequences may be either good or bad.

80 Examples Mother to daughter (who is on a diet): “If you eat that donut, then you will eat the whole box, and then you will gain back all of your weight, and then you will have to buy all new clothes and and a new car, and you will never get married. Mother to daughter: If you lose weight, you will become a beauty queen, and then a movie star, etc.

81 Straw Man Here the arguer misinterprets or misrepresents an argument or position for the purpose of attacking it. He or she then concludes that the real position has been refuted, when in fact the misrepresentation was refuted.

82 Examples Mr. X states: “My opponent in this debate has argued that our prisons release hardened criminals back into society. He recommends more rehabilitation. He mentioned job training, therapy, and other educational programs. Well, I certainly don’t like all the prison riots and so forth,but I don’t think that we should change prisons into schools and hospitals, and certainly not vacation resorts!!!!”

83 Red Herring You commit this fallacy when you introduce a “logically separate and irrelevant issue into the discussion.”

84 Examples You say that abortion is wrong and that it is murder. But do you know how many other ‘murders’ are committed by incompetent doctors everyday? A lot, that’s how many. You say that women should have the same rights as men? Now why is such a beautiful woman like yourself worried about such things? You should be worried about getting a rich husband.

Download ppt "Logical fallacies."

Similar presentations

Ads by Google