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Logical Fallacies

Logical Fallacies

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Logical Fallacies

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  1. Logical Fallacies A logical fallacy is a flaw in the argument’s logic.

  2. Why study examples BAD logic? • Oddly enough, logical fallacies are incredibly persuasive. Politicians and advertisers use them intentionally ALL the time. • If you understand logical fallacies, you can either: • Use them skillfully to manipulate people who listen to your arguments • Identify and defend against them in others’ arguments

  3. Ad Hominem • Literally means “against the man” or “against the person • What is attacked is the person making the argument rather than the argument itself • Ex: “I believe abortion is wrong.” “Of course you believe that, you’re a priest.” • What’s wrong here is that this person has come to their conclusion (you’re wrong about abortion) based on premises that don’t really connect to the conclusion (you’re a priest, priests have to say they’re against abortion).

  4. Appeal to Authority • “Did you hear? Dr. Oz said midgets are genetically inferior! I didn’t know that!” • While sometimes an appeal to authority is perfectly valid—obviously, sometimes we want to believe the established “experts”—it can turn into a logical fallacy when the so-called authority is for any reason not a credible person or who WAS a credible person but has recently fallen into disrepute. • And, as with all other arguments, your focus should be on the CONTENT of their argument, and not on the person making the argument.

  5. Appeal to Belief • Appeal to belief occurs when we base our logic on “everyone says it’s true, so it must be true” rather than on the facts or evidence. • For example, “Tons of people love Justin Timberlake and his music, so his music really must be good.” Well, it is a fact that JT makes amazing music, and if you don’t like his music, you’re wrong. But his music is objectively good on its own, not because we say it is. We’re just affirming this fact.

  6. Appeal to Common Practice • Closely related to appeal to popular belief. In this fallacy, you state that something is correct or morally okay practice simply because most other people do it. • Little kids use this to justify their actions a lot. Remember when your mom or dad would get mad and respond back to you, “If so-and-so jumped off a bridge, would you do that too?!”

  7. Appeal to Emotion • This is a very broad category of fallacy. It occurs when someone tries to manipulate you through your emotions, rather than giving a rational reasoning for something. • An easy example is the appeal to fear or “scare tactics” that many politicians use in the current shutdown/debt crisis debate • Also think of when your mom told you to stop crossing your eyes or your face would stick that way forever.

  8. Fallacy of Composition • The belief that the characteristics of the parts are the characteristics of the whole. • The Texans this year are a great example. We were all excited when everyone seemed healthy and ready to go at the beginning of the season. But having a lot of good players (including defensive player of the year!) who are in a healthy physical condition doesn’t mean they’re going to be the best team.

  9. Hasty Generalization • Basing a conclusion on too little evidence • It's a story, say, about Texas public schools. In the first paragraph a parent, apparently picked at random, testifies that they haven't improved. Readers are clearly expected to draw conclusions from this. But it isn't clear why the individual was picked; it isn't possible to determine whether she's representative; and there's no way of knowing whether she knows what she's talking about. Calling on the individual man or woman on the street to make conclusive judgments is beneath journalistic dignity. If polls involving hundreds of people carry a cautionary note indicating a margin of error of plus-or-minus five points, what kind of consumer warning should be glued to a reporter's ad hoc poll of three or four respondents?

  10. Slippery (downward) Slope • The mistaken conclusion that once X happens, Y will inevitably happen. The “inevitable” next event is usually much worse than the preceding event, with no truly logical connection between the two. • For example: “Once we allow same sex couples to marry, before you know it, polygamy and bestiality are bound to follow. People will be demanding to marry their cousins and pet goats and God know what else!”

  11. Straw Man • A fallacy in which, rather than attacking the argument, a distorted/incorrect version of the argument is attacked • For example “People who are pro-aboritiondon’t like babies.” Or, conversely, “People who are pro-life have no concern for women’s reproductive health or reproductive rights.”

  12. Equivocation • The same word is used with two different meanings. Or, it’s meaning is so vague that more than interpretation of the sentence could be deduced. • The sign said "fine for parking here", and since it was fine, I parked there. • All child-murderers are inhuman, thus, no child-murderer is human. 

  13. Faulty Analogy • This is a very common fallacy, but "False Analogy", its common name, is very misleading. Analogies are neither true nor false, instead they come in degrees from near identity to extreme dissimilarity. Here are two important points about analogy: • No analogy is perfect, that is, there is always some difference between analogs. Otherwise, they would not be two analogous objects, but only one, and the relation would be one of identity, not analogy. • There is always some similarity between any two objects, no matter how different. For example, Lewis Carroll once posed the following nonsense riddle: • How is a raven like a writing desk?

  14. Faulty Analogy continued • The point of the riddle was that they're not; alike, that is. However, to Carroll's surprise, some of his readers came up with clever solutions to the supposedly unsolvable riddle, for instance: • Because Poe wrote on both. • Some arguments from analogy are based on analogies that are so weak that the argument is too weak for the purpose to which it is put. How strong an argument needs to be depends upon the context in which it occurs, and the use that it is intended to serve. Thus, in the absence of other evidence, and as a guide to further research, even a very weak analogical argument may be strong enough. Therefore, while the strength of an argument from analogy depends upon the strength of the analogy in its premises, it is not solely determined by that strength.

  15. Begging the Question • You presented a circular argument in which the conclusion was included in the premise. • This logically incoherent argument often arises in situations where people have an assumption that is very ingrained, and therefore taken in their minds as a given. Circular reasoning is bad mostly because it's not very good. • Example: The word of Zorbo the Great is flawless and perfect. We know this because it says so in The Great and Infallible Book of Zorbo's Best and Most Truest Things that are Definitely True and Should Not Ever Be Questioned.

  16. Red Herring • A Red Herring is a fallacy in which an irrelevant topic is presented in order to divert attention from the original issue. The basic idea is to "win" an argument by leading attention away from the argument and to another topic. • http://www.youtube.com/watch?v=Jm7SK3C_jp0

  17. Illicit Major • A fallacy in which the major term is distributed in the conclusion but not in the major premise. • The predicate term of the conclusion refers to all members of that category, but the same term in the premises refers only to some members of that category. • All Texans are Americans, and no Californians are Texans, therefore, no Californians are Americans.The predicate term in the conclusion is 'Americans'. The conclusion refers to all Americans (every American is not a Californian, according to the conclusion). But the premises refer only to some Americans (those that are Texans). • Show that there may be other members of the predicate category not mentioned in the premises which are contrary to the conclusion.For example, from (i) above, one might argue, "While it's true that all Texans are Americans, it is also true that Ronald Regan is American, but Ronald Regan is Californian, so it is not true that No Californians are Americans."

  18. Illicit Minor • Like the illicit major only this time the undistributed term is in the minor premise • All communists are subversives, and all communists are critics of capitalism, therefore, all critics of capitalism are subversives.The subject term in the conclusion is 'critics of capitalism'. The conclusion refers to all such critics. The premise that 'all communists are critics of capitalism' refers only to somecritics of capitalism; there may be other critics who are not communists. • Show that there may be other members of the subject category not mentioned in the premises which are contrary to the conclusion.For example, from (i) above, one might argue, "While it's true that all communists are critics of capitalism, it is also true that Thomas Jefferson was a critic of capitalism, but Thomas Jefferson was not a subversive, so not all critics of capitalism are subversives."

  19. Affirming the Consequent • If A then B.B.Therefore, A. • If it rained, the streets are wet. • The streets are wet. • Therefore, it rained

  20. Denying the Antecedent • Any argument of the following form is invalid:If A then BNot ATherefore, Not B • Show that even though the premises are true, the conclusion may be false. In particular, show that the consequence B may occur even though A does not occur.

  21. Fallacy of Division • Assuming that what is true of the whole, is true of the individual parts • His house is about half the size of most houses in the neighborhood, therefore, his doors must all be about 3 1/2 feet high.

  22. Post Hoc • The mistaken belief that just because one thing happened before another, that it caused that other thing to happen.

  23. What Logical Fallacy Is This? • http://xkcd.com/162/

  24. False Dilemma • A limited number of options (usually two) is given, while in reality there are more options. A false dilemma is an illegitimate use of the "or" operator. Putting issues or opinions into "black or white" terms is a common instance of this fallacy. • Examples:Either you're for me or against me. • America: love it or leave it. • Either support Meech Lake or Quebec will separate. • Every person is either wholly good or wholly evil. • Identify the options given and show (with an example) that there is an additional option.