Master List of Logical Fallacies

1. Ad hominem or ATTACKING THE PERSON. Attacking the arguer rather than his/her argument. Saying something negative about someone is not automatically ad hominem. If a person (politician for example) is the issue, then it is not a fallacy. Example: John's objections to capital punishment carry no weight since he is a convicted felon. 

2. Ad ignorantium or APPEAL TO IGNORANCE. Arguing on the basis of what is known and can be proven. If you can't prove that something is true then it must be false (and vice versa). Example: You can't prove there isn't a Loch Ness Monster, so there must be one. 

3. Ad verecuniam or APPEAL TO AUTHORITY. This fallacy tries to convince the listener by appealing to an expert. Often times it is an authority in one field who is speaking out of his field. Example: Sports stars selling cars or hamburgers. Or, the actor on a TV commercial that says, "I'm not a doctor, but I play one on TV." 

4. AFFIRMING THE CONSEQUENT. An invalid form of the conditional argument in which the second premise affirms the consequent of the first premise and the conclusion affirms the antecedent. Example: If he wants to keep the job, then he will work hard. He is working hard, therefore he wants to keep the job. 

5. AMPHIBOLY. A fallacy of syntactical ambiguity deliberately misusing implications. Example: "Three out of four doctors recommend this type of pain relief!" The implied assertion here is that three out of four means seventy-five percent of all doctors and that this type of pain relief means this particular pain reliever. 

6. APPEAL TO EMOTION. In this fallacy, the arguer uses emotional appeals rather than logical reasons to persuade the listener. The fallacy can appeal to various emotions including pride, pity, fear, hate, vanity, or sympathy. The appeal to sympathy is actually a formal fallacy labeled ad misericordiam. Generally, the issue is oversimplified to the advantage of the arguer. Example: In 1972, there was a widely-printed advertisement printed by the Foulke Fur Co., which was in reaction to the frequent protests against the killing of Alaskan seals for the making of fancy furs. According to the advertisement, clubbing the seals was one of the great conservation stories of our history, a mere exercise in wildlife management, because "biologists believe a healthier colony is a controlled colony." 

7. ARGUMENT FROM ANALOGY or FALSE ANALOGY. An unsound form of inductive argument in which an argument is based completely or relies heavily on analogy to prove its point. Example: This must be a great car, for, like the finest watches in the world, it was made in Switzerland. 

8. BEGGING THE QUESTION. An argument in which the conclusion is implied or already assumed in the premises. Also said to be a circular argument. Example: Of course the Bible is the word of God. Why? Because God says so in the Bible. 

9. SLIPPERY SLOPE. A line of reasoning in which there is no gray area or middle ground. It states that x, y, z are implicit in step a. The primary characteristic is that it fails to distinguish between (or among) degrees of difference. It argues for (or against) the first step because if you take the first step, you will inevitably follow through to the last. Example: We can't allow students any voice in decision making on campus; if we do, it won't be long before they are in total control. 

10. COMMON BELIEF. This fallacy is committed when we assert a statement to be true on the evidence that many other people allegedly believe it. Being widely believed is not proof or evidence of the truth. Example: Of course Nixon was guilty in Watergate. Everybody knows that.  

11. PAST BELIEF. A form of the COMMON BELIEF fallacy. The same error in reasoning is committed except the claim is for belief or support in the past.  

12. CONTRARY TO FACT HYPOTHESIS. This fallacy is committed when we state with an unreasonable degree of certainty the results of an event that might have occurred but did not. Example: If President Bush had not gone into the Persian Gulf with military force when he did, Saddam Hussein would control the world's oil from Saudi Arabia today. 

13. DENYING THE ANTECEDENT. An invalid form of the conditional argument in which the second premise denies the antecedent of the first premise, and the conclusion denies the consequent. Example: If he wants to keep his job, he will work hard. He does not want that job, so he won't work hard. 

14. DIVISION. This fallacy is committed when we conclude that any part of a particular whole must have a characteristic because the whole has that characteristic. Example: I am sure that Karen plays the piano well, since her family is so musical. 

15. FALSE DILEMMA (often called the either/or fallacy because the argument nearly always includes the words "either... or..."). This fallacy assumes that we must choose between two opposite extremes instead of allowing for other possibilities, especially for the possibility of choosing an alternative between the extremes. Example: Women need to be either brilliant or beautiful to survive in this world. 

16. EQUIVOCATION. This fallacy is a product of semantic ambiguity. The arguer uses the ambiguous nature of a word or phrase to shift the meaning in such a way as to make the reason offered appear more convincing. Example: An ad from a sugar company says "Sugar is an essential component of the body, a key material in all sorts of metabolic processes, so buy some P&R sugar today." The word "sugar" is being used with two definitions that the ad does not acknowledge. 

17. FAR-FETCHED HYPOTHESIS. A fallacy of inductive reasoning that is committed when we accept a particular hypothesis when a more acceptable hypothesis, or one more strongly based in fact, is available. Example: The African-American church was set afire after the civil rights meeting last night; therefore, it must have been done by the leader and the minister, in order to cast suspicion on the local segregationists. 

18. HASTY GENERALIZATION. A generalization accepted on the support of a sample that is too small or biased to warrant it. Example: All men are rats! Just look at the louse that I married. 

19. Post Hoc Ergo Propter Hoc. A form of a hasty generalization in which it is inferred that because one event followed another it is necessarily caused by that event. Example: Mary joined our class and the next week we all did poorly on the quiz. It must be her fault. 

20. INCONSISTENCY. A discourse is inconsistent or self-contradicting if it contains, explicitly or implicitly, two assertions that are logically incompatible with each other. Inconsistency can also occur between words and actions. Example: A woman who demands equal rights and represents herself as a feminist, yet is upset when a date expects her to pay half. 

21. Non sequitur. In this fallacy the premises have no direct relationship to the conclusion. This fallacy appears in political speeches and advertising with great frequency. Example: A waterfall in the background and a beautiful girl in the foreground have nothing to do with an automobile's performance. 

22. QUESTIONABLE CAUSE. The fallacy of questionable cause is committed when, on insufficient evidence, we identify a cause for an occurrence that has taken place or a fact that is true. Example: I can't find the checkbook; I am sure that my husband hid it so I couldn't go shopping today. 

23. RED HERRING. This fallacy introduces an irrelevant issue into a discussion as a diversionary tactic. It takes people off the issue at hand; it is beside the point. Example: Many people say that engineers need more practice in writing, but I would like to remind them how difficult it is to master all the math and drawing skills that an engineer requires. 

24. SLANTING. A form of misrepresentation in which a true statement is made, but made in such a way as to suggest that something is not true or to give a false description through the manipulation of connotation. Example: I can't believe how much money is being poured into the space program (suggesting that 'poured' means heedless and unnecessary spending). 

25. STRAW MAN. This fallacy occurs when we misrepresent an opponent's position to make it easier to attack, usually by distorting his or her views to ridiculous extremes. This can also take the form of attacking only the weak premises in an opposing argument while ignoring the strong ones. Example: Those who favor gun-control legislation just want to take all guns away from responsible citizens and put them into the hands of the criminals. 

26. TWO WRONGS MAKE A RIGHT. This fallacy is committed when we try to justify an apparently wrong action by charges of a similar wrong. The underlying assumption is that if they do it, then we can do it too and are somehow justified. Example: Supporters of apartheid are often guilty of this error in reasoning. They point to U.S. practices of slavery to justify their system. 

TWO MAIN CATEGORIES OF LOGIC

INDUCTION, DEDUCTION: Inductive reasoning is required when you cannot ascertain the absolute certainty of the conclusion based on the given evidence, but you can establish probability. Deductive reasoning can be used when the premises (reasons, facts, evidence, etc.) prove WITH ABSOLUTE CERTAINTY that the conclusion is true, assuming that the premises are true. HYPOTHETICAL SYLLOGISMS--CONDITIONAL ARGUMENTS EXERCISE Hypothetical syllogisms (conditional arguments) can have two valid and two invalid structures. The two valid structures are affirming the antecedent (modus ponens) and denying the consequent (modus tollens). The two invalid structures, or fallacies, are denying the antecedent and affirming the consequent. SAMPLE: Chris and Nick would be very happy if the Browns beat the Steelers. The Browns did beat the Steelers, so Chris and Nick are very happy, indeed. SYLLOGISM VALIDITY TESTING EXERCISE To be a valid syllogism, the conclusion must be proven by the reasons. In formal logic, the terms must be nouns rather than adjectives. The first example includes the formal language in parenthesis. 1. All zebras have stripes. (All things that are zebras are things that have stripes) No zebras are polar bears. (No things that are zebras are things that are polar bears) Therefore, no polar bears have stripes. (Therefore, no things that are polar bears are things that have stripes.)