FALLACIES OF EVIDENCE Examples and Patterns Inappropriate Appeal

Inappropriate Appeal to Authority The rocket scientist, Dr. Quian Xuesen, is one of the

Appeal to Ignorance There is nothing in Mr. Johnson’s file indicating that he is

False Alternatives Look, do you want to save the planet or do you want

Loaded Question Highway Patrolman to Driver: “Just when did you realize that you were

Questionable Cause Post Hoc Right after the school board of Dover prohibited the teaching

Questionable Cause Mere Correlation Every time there’s a full moon, I’ve noticed the next

Questionable Cause Oversimplified Cause Test scores at the public high school in Eastern Los

Hasty Generalization small sample I noticed in the news this morning that there were

Hasty Generalization Biased or Unrepresentative Sample Fifteen of the twenty students I interviewed this

Slippery Slope You should never gamble. Once you start gambling you find it hard

Weak Analogy Banning the use of Methyl Bromide, the pesticide farmers use to prevent

Inconsistency Jake: Nobody goes to Margie’s Restaurant anymore. Sally: Why not, that place was

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FALLACIES OF EVIDENCE Examples and Patterns

Inappropriate Appeal to Authority The rocket scientist, Dr. Quian Xuesen, is one of the most respected and honored Chinese scientists of this century. He is in favor of free elections in China. Don’t you think this is an idea whose time has come? Here, the authority cited, though highly regarded in his field of expertise, lacks relevant expertise on the issue addressed in the argument.

Appeal to Ignorance There is nothing in Mr. Johnson’s file indicating that he is not a communist. Therefore we can safely conclude he is a communist. Pattern: We have no evidence against a claim X. Therefore, claim X is true. We have no evidence for claim X. Therefore, claim X must be false.

False Alternatives Look, do you want to save the planet or do you want to create jobs? In this recession, we can’t afford to slow down the growth of business with messy environmental regulations. Pattern: The author asserts you must accept either A or B (but where A and B do not exhaust the plausible possibilities or where the given alternatives are not mutually exclusive). The author rejects all but one of the named alternatives The author concludes the remaining alternative must be true.

Loaded Question Highway Patrolman to Driver: “Just when did you realize that you were speeding? ” Pattern: Author asks a question that entails an objectionable assumption(s). Yet, there is no way to directly answer the question without tacitly accepting the underlying assumption(s).

Questionable Cause Post Hoc Right after the school board of Dover prohibited the teaching of Creationism in high school biology courses, the city was struck with a devastating tornado. That’s what happens when you make God angry! Pattern: Event B occurred immediately after event A. Therefore, event A must have caused event B.

Questionable Cause Mere Correlation Every time there’s a full moon, I’ve noticed the next day that some terrible crime is reported in the news. I wouldn’t go out during a full moon if I were you. People get pretty crazy. Pattern: Event (or condition) A and event (or condition) B regularly occur together Thus, event A must be the cause of event B.

Questionable Cause Oversimplified Cause Test scores at the public high school in Eastern Los Angeles are considerably lower than scores at Beverly Hills College Preparatory Academy. I suppose it must be because so many of the students at East LA High speak English as a second language. Pattern: An author cites a plausible causal factor X as the entire explanation for some event (or condition) Y, but where there are likely myriad complex causes of X. The author concludes that X is the sole (or primary) cause of Y.

Hasty Generalization small sample I noticed in the news this morning that there were three accidents over the weekend, all involving drivers who had recently immigrated to the US. Isn’t it time to crack down on these people? We need to make our roads safe again. Pattern: The author cites evidence from a sample that is too small (relative to the size of the population in question). The author draws a general conclusion about the population.

Hasty Generalization Biased or Unrepresentative Sample Fifteen of the twenty students I interviewed this morning during my freshman composition class said they thought the legal drinking age should be lowered to 18. I guess most people agree that this would make good policy. Pattern: The author cites evidence from a sample that is biased (does not reflect the diversity in the population in question). The author draws a general conclusion about the population.

Slippery Slope You should never gamble. Once you start gambling you find it hard to stop. Soon you are spending all your money on gambling, and eventually you will turn to crime to support your earnings. Pattern: Event A is said to inevitably lead to event B, C, (and so on). Event’s B, C (and so on) is/are unacceptable. Thus event A must be avoided.

Weak Analogy Banning the use of Methyl Bromide, the pesticide farmers use to prevent mold growth in strawberries, is like banning taxi drivers from using cars. Surely such a move would destroy the industry. Pattern: X is like Y in that they both share properties a, b, and c. (but really there are significant relevant differences between X and Y) Y has property P. Therefore, X has property P.

Inconsistency Jake: Nobody goes to Margie’s Restaurant anymore. Sally: Why not, that place was great. Jake: Well, its just too crowded to get a reservation. Pattern: The author asserts more than one proposition such that the propositions cannot all be true. Or, the author asserts a statement that is selfreferentially inconsistent.