Which of the following is the most serious weakness of this argument? a. It assumes that it is wrong to break tradition. b. It assumes that women should not have an equal opportunity. c. It assumes that including women would mean that everyone would have to be included without restriction. d. It does not acknowledge that men are included in some women’s tournaments. e. It does not explain why the tournament is such a renowned event. This argument has many problems, including the fact that in general, it does not offer any truly logical reasons to support its conclusion. Of the options given, the best choice is c. This assumption is a slippery slope fallacy. Including women would not mean anyone could enter the tournament. This slippery slope is used as a sort of scare tactic to frighten off support for including women in the tournament. GMAT questions will often ask you to determine what evidence strengthens or weakens an argument or what information would help you better evaluate an argument. Now that you have reviewed the elements of evaluating arguments, take another look at this question from the pretest: 13. DNA evidence has increasingly been used in court to prove guilt and to exonerate the innocent. Because so many convicted felons have been cleared by DNA evidence, all cases in which someone was convicted largely on circumstantial evidence should be called into question and reviewed. Which of the following, if true, would most strengthen this argument? a. One in three convictions today rests largely on DNA evidence. b. DNA evidence is admissible even after the statute of limitations has expired. c. Of every ten cases in which DNA evidence becomes available post-conviction, five convictions are overturned. d. DNA evidence is 99.8% accurate. e. DNA evidence is very difficult to falsify or tamper with. To answer this question, you need to evaluate each of the options. The key question is which choice is the most relevant to the argument. As discussed earlier in this chapter, this is a controversial conclusion, so it should be backed by very strong evidence. Which of these claims provides the best support for the argument? The best choice is c. The fact that would most strengthen this argument is the percentage of cases in which DNA evidence overturned prior convictions. If a full half of all cases resulted in erroneous convictions that were later cleared by DNA evidence, then that should certainly draw other convictions into doubt. That means that potentially half of all felons have been wrongly convicted. The fact that one in three of today’s con- victions rest on DNA evidence has no bearing on prior convictions, so choice a is irrelevant. Similarly, the admissibility of DNA evidence (choice b) has no bearing on the quality of prior convictions; it is also irrel- evant. That DNA evidence is accurate (choice d) and difficult to tamper with (choice e) strengthens the argu- ment for the use of DNA evidence in court, but it does not directly strengthen the argument that prior convictions should be called into doubt. – CRITICAL REASONING– 103 Evaluating Explanations Many of the critical reasoning questions on the GMAT exam will either present a scenario and ask you to determine the best explanation for a phenomenon or offer an explanation and ask you to evaluate that expla- nation. Some special criteria must be considered when judging an explanation. A good explanation is based on the following criteria: ■ Testable. An explanation must be subject to testing. If the phenomenon is the only evidence for its existence, then it is a poor explanation. If it cannot be tested for correctness, then you cannot deter- mine whether or not it is correct. If an explanation cannot be verified or refuted under any circum- stances, regard it with suspicion. Example: He knew what I was thinking because he has ESP. Although many have tried to prove that extra-sensory perception (ESP) exists, tests remain inconclu- sive. And how could you test whether or not this was true? If you test him for ESP and he fails, he could claim that he only uses his ESP powers when he wants to. This is an untestable explanation. ■ Noncircular. If the phenomenon and the evidence/explanation for the phenomenon are essentially the same, then you have a circular (and therefore unacceptable) explanation. (This works just the same as the circular reasoning logical fallacy.) Beware of any explanation that merely restates the phenomenon it is supposed to explain. It may look like an explanation because it restates the phenomenon in differ- ent words, but no explanation is really being offered. Example: Prices keep going up because of inflation. Inflation means that prices are going up; this doesn’t explain why prices are rising. ■ Precise. If an explanation is excessively vague, it does not really explain the phenomenon. Example: Our society is a mess because of TV. This is an exceptionally vague explanation. What does the speaker mean by “a mess”? What does she mean by “because of TV”? ■ Reliable and relevant. A reliable explanation is one that people can use to predict other behaviors. If an explanation leads to predictions that turn out to be false, then it is unreliable. Example: The Watsons are always late because they only have one car. Based on this explanation, you would have to expect that every family that has only one car will always be late. Clearly, this will lead to false predictions, proving this is an unreliable explanation. In addition, the fact that the Watsons have only one car is irrelevant to their punctuality. Families with no cars might always be on time; families with four cars might always be late. This is also an irrelevant explanation. – CRITICAL REASONING– 104 ■ Able to explain more phenomena. Other things being equal, the more phenomena an explanation explains, the better the explanation, especially for scientific theories. Example: Rent is high in this neighborhood because 1. landlords are greedy. 2. there is a new train line that goes directly to the city. Clearly, the second explanation here is better. It can explain more phenomena, such as an increased demand for apartments, an increase in local property taxes, an increase in population, and an increase in upscale retail establishments in the area. ■ Consistent with well-established theory/common knowledge. Although established theories are not infallible (remember, people once thought the world was flat), you need very powerful evidence to dis- card them. So, if an explanation conflicts with such a theory, you have good reason to be suspicious. Likewise, if an explanation conflicts with your common knowledge, be on guard. It is probably not a good one. Example: That little girl has tons of freckles, just like her parents. They all must spend way too much time in the sun. Although it’s true that sun exposure can cause some people to develop freckles, this explanation goes against the well-established theory of heredity. If a little girl has freckles and her parents also have freckles, it is safe to assume she inherited the freckle gene from her parents. Returning to the bookstore question about the placement of romance novels, you can further assess the possible conclusions with these criteria for evaluating explanations. You could test all of the choices to see if they are correct, none are circular, and all have explanatory power. But a — that customers would come back for another romance novel — is not reliable or relevant to the scenario. Return purchases have nothing to do with the placement of books in the store. Common Flaws in Causal Arguments Arguments about cause (why things happen) contain their own types of fallacies that you should watch out for, including the following: ■ post hoc, ergo propter hoc ■ ignoring possible common cause ■ assuming common cause ■ reversing causation POST HOC, ERGO PROPTER HOC Translated from Latin, this means “after this, therefore because of this.”This argument assumes that X caused Y just because X preceded Y. For example, As soon as Thompson took office, the market crashed. He has simply destroyed the economy. – CRITICAL REASONING– 105 The problem with this argument is that although X (Thompson’s taking office) preceded Y (the mar- ket crash), that does not mean Thompson caused the market crash. The key question to ask is this: Is X the only relevant change prior to Y? In this case, definitely not. Many, many other relevant factors could have pre- ceded the market crash. (Besides, it is difficult for a politician to destroy the economy “as soon as” he or she takes office. Common sense tells you it would take some time for a leader’s policies to have an impact.) IGNORING P OSSIBLE COMMON CAUSE This argument assumes that X caused Y, but maybe X and Y were both caused by another factor (W). For example, I had hives because I had a fever. Perhaps the fever caused the hives, but maybe the hives and the fever were both caused by another fac- tor, such as a virus. Before accepting a causal explanation, ask the following: Could there be an underlying cause for both X and Y? A SSUMING COMMON CAUSE This argument assumes that X and Y had a common cause and ignores the possibility of a coincidence. Maybe X and Y are due to different or multiple causes. For example, On Thursday, there was a black cat sitting in my driveway. That night, I had an accident in my car. On Friday, the cat was there again, and that night, my boyfriend broke up with me. That black cat sure brought me some bad luck. Besides the fact that this argument does not have much initial plausibility (and requires belief in the superstition that black cats bring bad luck), it fails for several other reasons: ■ It ignores the possibility of coincidence. ■ It does not consider the fact that a black cat is totally irrelevant to the occurrences. ■ It does not consider other possible common causes (maybe the accident and the breakup were both due the speaker’s inability to pay attention — to the road and to her boyfriend). ■ It does not consider that the two events could have resulted from very different causes (the accident could have been because the speaker was distracted; the breakup could have been caused by an infi- delity, a change of heart, and so on). REVERSING CAUSATION This fallacy confuses cause and effect (the “chicken and the egg” problem), arguing that the effect was really the cause or vice versa. For example, Lucy feels more confident because she aced her last two exams. – CRITICAL REASONING– 106 This example could definitely be a case of reversed causation. Maybe Lucy aced her last two exams because she was feeling more confident. You would have to study the situation further to determine which was cause and which was effect. If you suspect reverse causation, consider carefully whether a reversal of cause and effect could have occurred. Is it possible for the alleged cause to actually be an effect, or the effect to really be the cause? Now take a look at the following question. Use your knowledge of causal argument fallacies to answer it correctly: Did you ever notice that successful business people drive expensive cars? If I get myself an expensive car, I will become more successful. The most serious flaw in this argument is a. it assumes all successful business people drive expensive cars. b. it reverses cause and effect. c. it is not a testable explanation. d. it ignores the possibility of coincidence. e. it ignores a possible common cause. The correct answer is b: The argument reverses cause and effect. Successful business people can afford expen- sive cars because they are successful; the success comes first, then the car. The speaker may be looking at some serious debt if he believes otherwise. – CRITICAL REASONING– 107 . strengthen the argument that prior convictions should be called into doubt. – CRITICAL REASONING– 103 Evaluating Explanations Many of the critical reasoning questions on the GMAT exam will either. all felons have been wrongly convicted. The fact that one in three of today’s con- victions rest on DNA evidence has no bearing on prior convictions, so choice a is irrelevant. Similarly, the admissibility. out to be false, then it is unreliable. Example: The Watsons are always late because they only have one car. Based on this explanation, you would have to expect that every family that has only one