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Philosophy 103: 
Introduction to Logic
Review Exercises

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REVIEW EXERCISES

Directions: Please indicate the best answer to the fallacies in the following passages.  Not all passages necessarily contain fallacies.  Fallacies present here include those of relevance and presumption.

1. Einstein became a great physicist because his parents and his teachers left him alone to dream.  Had they badgered him to study, he never would have gotten beyond the Swiss patent office.

Answer:  Since there is no causal connection between "leaving someone alone to dream" and "becoming a great physicist," the fallacy of false cause occurs.

2. As I drove to school this morning, not one car which was turning had its turn signal on.  Thus, I conclude that the drivers in this state are not well trained since they do not ever use their turn signals.

Answer: The number of examples and the method of selection are not reliable methods of generalization; hence, the fallacy of converse accident occurs

3. The best definition distinguishing man from the other animals is that man is a rational animal.  Therefore, you, as a person, should spend more time studying and using your brain than you should spend for having a good time.

Answer: Although all persons, as human beings, have rational capacities, it does not follow that in this specific case one should necessarily be rational more often--fallacy of accident is committed.

4. I can see that you are greatly impressed by the power of logic and argument.  Therefore, are you going to sign up for Philosophy 102: Introduction to Philosophic Inquiry this semester or next semester? It's got to be one or the other.

Answer: The question presupposes that the listener will sign up for a logic course; hence, the fallacy of complex question occurs.

5. The Smithson Foundation is investigating whether or not police officers are using excessive force in traffic arrests of minorities.  Hence, we may conclude  that some police officers, at least, use excessive force in that kind of arrest.

Answer: An investigation does not entail that any evidence has been forthcoming so far. Since no evidence is adduced, one cannot justifiably come to a conclusion. The fallacy of ad ignorantiam occurs in this passage.

6. The testimony of the defendant accused of manslaughter in this indictment should be disallowed because she has been arrested for shoplifting on many occasions.

Answer: Strictly speaking, one should evaluate the cogency of the testimony and evaluate it on its own merit. Fallacy of ad hominem occurs because being a shoplifter does not entail not telling the truth.

7. Why haven't you written to your Mother often as you should?  You would feel much better about yourself if you would attend to the details of life which are this important.

Answer: The supposition that the Mother is not written to sufficiently often is assumed without evidence and is used as the evidence for drawing another conclusion; hence, the fallacy of complex question is committed.

8. It should be no surprise to you that the state is, again, headed into either a recession or perhaps a deep economic downturn.  After all,  a Republican has just been elected governor.

Answer: The locutor assumes, without evidence, that the election of a Republican will cause a slowing down of the economy. The fallacy of false cause occurs.

9. When I was shopping at Bess's Fine Clothing, not one person gave me the time of day.  I guess Bess's is not a very friendly place to work.

Answer: The speaker is generalizing from one experience. More evidence would be necessary to reach the conclusion that Bess's is not a good place to work. The speaker commits the fallacy of converse accident.

10. John Bardeen, a professor at the Advanced Institute of Physics, has gone on record to say that the American Medical Association needs to raise its standards for physicians.  The opinion of a man of that brilliance should not be disregarded.

Answer: An authority in physics is being cited outside of his field of expertise. The ad verecundiam fallacy occurs11. Simply from the fact that most persons believe a statement is true, it does not follow logically that the statement is true--ad populum fallacy.

11. If we took a poll right now, almost every American would agree that a vaccine for AIDS will soon be found.  Therefore there can be little doubt that AIDS will be practically wiped out in the near future.

Answer: Simply from the fact that most persons believe a statement is true, it does not follow logically that the statement is true--ad populum fallacy.

12. I made low grades on my first tests in math and English.  I must really be dumb.

Answer: Too few examples are used to justify such a conclusion; fallacy of converse accident is committed.

13. As a daughter when I was four, my father taught me the beauty of numbers, and I have excelled at mathematics ever since.  My conclusion on why females do not score as high on math tests?  The males with a high aptitude for mathematics are not spending enough time with their daughters.

Answer: The author of this example assumes that her case would be typical of all or most other daughters if they had had similar experiences. The fallacy of converse accident occurs.

14. I think that the tests given in this class were more than fair, and I think you will agree with me because, if you do not, your grade in this course will certainly be in jeopardy.

Answer: The threat of a poor grade is logically unrelated to the fairness of tests; hence the ad baculum fallacy is committed.

15. The result of my doing well in economics is very simple.  I eat Post Toasties for breakfast every morning for breakfast, and this breakfast helps my ability to analyze in great depth.  I think it must be all those complex carbohydrates.

Answer: No causal evidence is given for the relation between eating a breakfast cereal and ability to analyze, so the fallacy of false cause occurs.

16. Oriental Philosophy is the best course taught at Lander University.  I know this because all of my friends say so.

Answer: Although most friends think so, that doesn't make it so.  Ad populum fallacy occurs.

17. Look Mr. IRS examiner, of course I owe taxes--I'm not denying that.  However, I was unable to file on time because my wife was sick and my two children need my attention.  Surely the IRS is not opposed to keeping the family together.

Answer: The unfortunate circumstances of the taxpayer are logically independent of his responsibility to pay his taxes--ad misericordiam fallacy.

18. Mr. Smith, maybe there is some truth in what you say about me being rude to sales people, but I have certainly heard may sales people complain about your manners, so you are certainly not the person to point this out to me.

Answer: The ad hominem variation of "you're another" or tu quoque is offered.

19.  Sir, don't you want to look more closely at our aluminum siding for your new home?  When we put this up your home will take on the glow of beauty, and you will be admired by others as someone who cares.  Not only that, but your life will be richer as you invite with pride others to your home to share the better way of life.

Answer: Some logicians would classify this passage of an instance of the ad populum fallacy. However, the passage is regarded here as "rhetoric and persuasion."

20. It is easy to see that goodness is in the world and not just in our minds, because as we look at the world, some things are obviously not evil in themselves.

Answer: Although "good" and "evil" are not complementary classes, this passage can be anaylzed as petitio principii, since ceteris paribus the meanings are similar enough to be circular reasoning. If this analysis is acceptable then, in a sense, this fallacy turns of the fallacy of false dichotomy.

21. Mr. Watkins has clearly and concisely detailed his arguments concerning the relative safety of tobacco products for third world countries.  But, let me remind you that we could hardly expect him to say anything else because he has worked in the tobacco industry for the last twenty years.

Answer: Although Mr. Watkins worked for the tobacco industry, it does not follow necessarily that he does not speak the truth. One might even offer the argument that his expertise is actually relevant to the subject of the argument. Fallacy of ad hominem is committed.

22. All persons act in order that they might get pleasure.  Even so-called altruistic persons who help others so much that they do almost nothing for themselves get pleasure out of giving.  Otherwise, they wouldn't do it.  Suppose a person hits himself over the head with a hammer.  He must get pleasure from it, because why else would he do it if he didn't get pleasure from it?

Answer: The fallacy is petitio principii or circular argument. The premiss that all persons act from the motive of pleasure is the same statement as the conclusion.

23. The Roper Organization says that more persons watch CBS's 60 Minutes that any other news program on television.  Therefore, it must be the best news programming on TV.

Answer: Simply because a program is popular, the conclusion doesn't logically follow that the program is the best--unless, of course, one defines "best" as "the most popular" as is sometimes done in marketing. Logically speaking, the fallacy of ad populum occurs.

24.  Hilda Robinson, an old backwoods, ignorant lady who never got past the fourth grade in school, claims that chicken soup is good for a cold.  What does she know?  She is ignorant of the scientific evidence.

Answer: The attack on character and circumstances is characteristic of the ad hominem fallacy.

25. Watch the Business Report at 7:00 on channel 6.  It's the best report on current dealings on Wall Street because no comparative study of business reposts has ever proved to our satisfaction that there is any better.

Answer: From the fact that a conclusion has not been proved, no other conclusion can be drawn. This passage illustrates one common version of the ad ignorantiam fallacy.


If you would like additional practice, more exercises on fallacy identification can be found by clicking the links below.
Example Logic Quizzes 
Test on Informal Fallacies
Example Scientific Reasoning Quizzes
Test on Scientific Reasoning Fallacies

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