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  1. Philosophy 103Linguistics 103Even MoreIntroductory Logic: Critical Thinking Dr. Robert Barnard

  2. Last Time: • Basic Concepts: • Deductive/Inductive • Valid/Invalid • Strong/Weak • Sound • Cogent • Started Informal Fallacies

  3. Plan for Today Try to wrap up Informal Fallacies Time Permitting: Some Philosophical Issues

  4. Fallacies Review • Fallacy =df “A fallacy is a mistake in an argument which consists in something other than merely false premises” • Fallacies of Relevance • Appeal to Force (Ad Bacculum) • Appeal to Pity (Ad Misericodium) • Appeal to the People (Ad Populum)

  5. Attacking the source of an argument instead of the argument itself. 4. Argument against the Person (Ad hominem)

  6. 4. Argument against the Person (Ad hominem) (2) Ad Hom. Abusive: John Kerry says that we should spend more state revenue on education because doing so would result in a more productive workforce. But Kerry is a bleeding-heart, liberal Yankee from Massachusetts -- so you know that his opinion is worthless.

  7. 4. Argument against the Person (Ad hominem) (3) Ad Hom. Circumstantial: Barnard says that we should spend more state revenue on education. But Barnard is a professor who wants a better salary -- so you know that his opinion is worthless.

  8. 4. Argument against the Person (Ad hominem)(4) Ad Hom FromHypocrisy: You've claimed that smoking is bad for one's health; but you smoke too. Think about:

  9. 4. Argument against the Person (Ad hominem) (5) Think about: Credibility: if a person with low credibility asserts something without supplying evidence for it, then we should withhold judgment. Reasons: if the person does supply reason for the claim, then we still need to look at those reasons and evaluate whether they support the conclusion in question. Contradictory beliefs. If we can show this, then we have indeed supplied a good reason to believe that the person is confused. People can change their minds. Changing your mind is fine; contradictory beliefs are not.

  10. Applying a general rule to a case it was not designed to cover. Example: Killing is bad: therefore, it was wrong for us to go to war against the Nazi's. 5. Accident

  11. Attacking an oversimplified version of an opponent's actual position. Example: Those who support gun control are wrong; they believe that no one should have the right to defend themselves in any situation. 6. Straw Man

  12. Two closely related fallacies, which involve diverting the listener's attention by changing the subject or drawing a slightly different conclusion than the one that should be drawn. Example: The death penalty is the only way to punish criminals. Why? Because the justice system in this country has gone straight to hell -- what with murderers, rapists and robbers getting off scot-free! It has got change! 7. Missing the Point/Red Herring

  13. Another (Common) Red Herring: Tom: Johnson wants the government to pay its bills, and not borrow anymore money. Joe: But Johnson is a tax-and-spend big-government politician. Anything he says must be wrong! Note: Red Herring bleeds into Ad Hom.

  14. With these sorts of fallacies, the problem is that the premises provide extremely weak support for the conclusion. They often disguise this fact by involving an emotional appeal of some sort. Fallacies of Weak Induction

  15. Arguing for a conclusion based on the testimony of someone who is not qualified to speak on the relevant subject. Example: Be careful and look out for lions when you go hunting next weekend; Coach O says that lions migrate south during the winter in the United States. 1. Argument from Unqualified Authority

  16. Drawing a conclusion based on a premise which states that nothing has been shown. Example: No one has ever proven that ghosts don't exist. Therefore, they obviously do. 2. Appeal to Ignorance

  17. What I saw on “Meet the Press” Russert: So can you produce actual evidence that there were WMDs in Iraq? Talking Head: Can you prove there weren’t? Russert’s Problem: HE DID NOT CALL THE TALKING HEAD ON THE FALLACY!!!

  18. Exception: Arguments from Ignorance For Ignorance Example: You have consistently failed to demonstrate your knowledge of the material on the exam. Therefore, I don't think you know the material. (Ignorance IS evidence of ignorance…)

  19. A very bad inductive generalization. Example: All three of the Ole Miss students I've met so far have been from Mississippi; so there must be no out-of-state students here. 3. Hasty Generalization

  20. Stating that there is a causal connection when one probably does not exist. There are different types: Arguing from Coincidence: Example: When I've used my lucky pen before, I've passed the test; therefore I'll fail if I don't use that pen. (Post Hoc Ergo Propter Hoc) Oversimplifying the Cause: Example: Our society is filled with violence and there is a lot of violence on TV. It is obvious that the violence in society is caused by people watching television. . 4. False Cause

  21. 4. False Cause (2) Slippery Slope: This is a very common variety of the false cause fallacy; it involves believing without any supporting reasons that X will lead to Y.

  22. “Slippery Slope” Example Legalizing marijuana will lead to the legalization of cocaine. If you legalize cocaine, you'll be able to buy crack and every other drug at your local 7-11. (In this argument, it is asserted that the legalization of marijuana will lead to (by degrees) the legalization of every drug. Once one accepts the legalization of marijuana, then one is assumed to be on the slippery slope towards the legalization of every drug)

  23. 4. False Cause (3) Sometimes slippery slope arguments are justifiable: for instance, if the reasons to accept x are just the same reasons that would lead you to accept y, then in accepting x, one should also accept y. BUT, this is because the reasons for X actually support Y!

  24. Making a weak analogy, or unfairly comparing one thing to something else. It is very difficult to evaluate analogies with any degree of precision. Example: Philosophy 101 is a philosophy class and has a lot of discussion; Logic is a philosophy class. So, it must also have a lot of discussion 5. Weak Analogy

  25. An example of Weak Analogy

  26. Fallacies of Meaning and Ambiguity Fallacies of this variety turn upon mistakes of and imprecision in language

  27. This can occur in several different forms. Essentially, this fallacy occurs when the key premise of an argument is unsupported. Here are some varieties of this common fallacy: Circular reasoning: Murders have lost the right to live because anyone who takes the life of another person has given up that right. 1. Begging the Question

  28. 1. Begging the Question (2) • Concealed Premise: Murder is always wrong. Therefore, the death penalty is wrong. (The concealed premise: The death penalty is murder).

  29. 1. Begging the Question (3) • Wishful Thinking: Of course there is life after death; if I didn't believe that, life would be too depressing.

  30. Dilbert begs the question…

  31. Sometimes called a "loaded question". A question which contains a hidden assumption or condition. Often, complex questions are such that no matter how you answer them, you may be acknowledging something you might not want to acknowledge. 2. Complex Question

  32. Complex Question Examples • When did you stop lying to your friends? • When are you going to give up being a Nazi? • When did you stop beating your dog? • How long has it been since your last illicit affair?

  33. Presents as a premise two alternatives as if they were the only two available when in fact there are more. Often the conclusion is only implied and not stated. Example: Either we elect Mr. X or the economy goes down the tubes. The choice should be obvious. 3. False Dichotomy or False Dilemma

  34. Avoid the False Dichotomy!! The way to avoid falling into this trap: Before you accept X because Y is false, make sure there isn't some other alternative that allows you to reject X as well.

  35. 4. Suppressed Evidence: An inductive argument which ignores overriding evidence which would prove a different conclusion. • This is common is advertising. Example: Rent-to-own: the cheaper way to buy! • Quoting out of context can also lead to this fallacy, as can ignoring current events.

  36. 5. Equivocation • Where the conclusion of the argument depends on the fact that a word is being used in two different senses due to semantic ambiguity (one word having two or more definitions). Example: Every child is a special person. Every person should vote against the school bond. Therefore, every child should vote against the school bond.

  37. 6. Amphiboly: • Where the conclusion of the argument depends on the fact that a sentence is syntactically ambiguous. (i.e. the sentence allows for more than one interpretation of its meaning) • Ambiguity Example: John attacked the man with a knife. • Fallacy Example: Norris said he operates a small car repair shop. Therefore, you can't take your Cadillac to him. (This can be a real problem in legal documents).

  38. 7. Composition: • Mistaking properties of the parts for properties of the whole. • Example: Every member of the team is a winner; therefore the team is a winner. • Not every instance of this type of reasoning is bad. • Additive Quality Example: “Each one of these stamps is valuable. Therefore, the collection of stamps as a whole is valuable.”

  39. Even a Viking can do it…

  40. 8. Division: • Mistaking properties of the whole for properties of the parts. • Examples: • The Congress is based in Washington D.C. therefore each member of Congress is from D.C. • This football team is the best in the conference; therefore the quarterback is the best in the conference. • Again, not every instance of this reasoning is bad. Pay attention to the context and the details.

  41. Is the sun coming up, or going down….?

  42. The “Laws of Thought” • Identity • Non-Contradiction • Excluded Middle Are They all both General and Necessary?

  43. The Law of Identity “A true statement is true.” “All A is A.” “Everything is what it is, and not something else.” “Everything is self-identical.”

  44. The Law of Non-Contradiction “ Nothing A is not A” (a form of ‘identity’?) “No statement is both true and false at the same time.” “Nothing is both F and not-F at the same time.” “Opposite qualities are incompatible.” “Everything F is not not-F.”

  45. The Law of Excluded Middle “Every statement must be either true or false.” “If something is F then it is not not-F.” “Either F or not-F.”

  46. Logic and Psychology • Where do the laws of thought come from? • Are they generalizations upon experiences? • Could we arrive at their general correctness without having a variety of experiences?

  47. Logic and Rhetoric Rhetoric is the art of Persuasion Logic can be a part of Persuasion Informal Fallacies are persuasive cases that violate logic. Logic Teaches us to know the difference.