Think Again: How to Reason and Argue

by Walter Sinnott-Armstrong

  It need not always be a problem to ignore or dismiss an alternative explanation without argument. Some alternative explanations are so clearly inadequate that they do not deserve any effort at refutation. Every inference to the best explanation would need to be irritatingly long in order to deal with every fool alternative. Nonetheless, this failure to argue against an alternative does reduce the potential audience for the argument. It cannot reach anyone with any inclination to accept this alternative explanation.

  The most serious weakness in Powell’s argument lies not in the alternatives he does mention but in the alternatives he does not mention. This problem pervades inferences to the best explanation. Just recall any murder mystery in which a new suspect appears after the detectives thought that they had already solved the case. The same kind of possibility can undermine Powell’s argument, but here the suspects are hypotheses. To refute his argument, all Powell’s opponents need to produce is one other viable hypothesis that explains the relevant data at least as well as Powell’s.

  Notice that opponents do not have to produce a better alternative. If all they want to show is that he has not justified his conclusion, then all they need to show is that there is one alternative at least as good as his. If two alternative explanations tie for top place, then Powell’s argument cannot determine which of the top two is correct. In that case, Powell’s opponents win, because he is the one who is trying to argue for one of them over the other.

  Still, it might be hard to come up with even one decent alternative. Maybe Hussein was controlled by aliens who eat fissile material, but he did not want any for himself. You cannot falsify that alternative hypothesis if there is no way to detect the presence of such aliens. Nonetheless, these aliens would violate well-established laws of physics, so we have plenty of reason to dismiss this hypothesis as silly. A little more realistically, maybe Hussein had OCD (obsessive-compulsive disorder), and that is why he continually demanded more refined tubes. However, he did not show symptoms of OCD in other areas of his life, so there is no independent evidence that he had this mental disorder (though maybe he had others, such as narcissism). Hypotheses like these are clearly not even decent explanations.

  What we really need for a realistic explanation to be as good as Powell’s is some common and plausible motive that would make Hussein seek more and more refined aluminum tubes. Well, maybe he wanted to use these tubes in some innocent kind of manufacturing. Maybe, but that hypothesis lacks explanatory power—it cannot explain much—until we make it more specific. What kinds of products are such refined tubes needed to manufacture? The hypothesis that Hussein was planning to use the tubes to manufacture some other product also cannot explain why Hussein mentioned only conventional rockets in his defense. And Powell already rejected the rocket hypothesis.

  Thus, it is at least not easy to come up with any explanation that is as good as Powell’s. Of course, this difficulty might be due to my (and your?) lack of knowledge about rockets, fissile material, and Iraqi manufacturing. Even if we cannot come up with any viable alternative, there still might be some explanation that is as good as Powell’s. Nonetheless, in the absence of any such alternative, Powell’s argument does give some reason to believe his conclusion.

  Other problems arise, however, when we look closely at that conclusion. The conclusion of an inference to the best explanation is supposed to be the same as the hypothesis that explains the observations. However, people who use this form of argument often make subtle changes in their conclusions. That happens here. First, Hussein’s attempts to acquire the tubes occurred in the past. What explains these attempts is a desire at the past time when those attempts were made. However, the conclusion is about the present: Hussein desires—not desired—to produce fissile material for a nuclear bomb. Powell exchanged “s” for “d”! Moreover, the present tense is essential. Powell wants to justify invading Iraq soon after his testimony. His argument would not work if Hussein used to desire fissile material in the past but no longer has that desire at present. Thus, Powell at least owes us some reason to believe that Hussein has not changed.

  Similarly, what if Hussein still desires fissile material for a nuclear bomb, but he has little or no chance of getting any of what he desires? The Rolling Stones are right again: You can’t always get what you want. Then the conclusion that Hussein wants fissile material for nuclear bombs would hardly be enough to justify invading Iraq. A lot of other world leaders want nuclear bombs, but the United States is not justified in invading all of them. An invasion could be justified only if it would avoid some harm or danger, but a mere desire for nuclear bombs without any chance of fulfilling that desire would not be harmful or dangerous—or at least not harmful or dangerous enough to justify invasion. Thus, Powell also owes us some reason to believe that Hussein has a significant chance of getting nuclear bombs.

  These gaps show that Powell’s argument is at best incomplete. As always, my job here is not to determine whether he was correct, much less whether the United States was justified in invading Iraq. I doubt it, partly because of what we have learned in intervening years, but that does not matter in this context. My goal is only to understand Powell and his argument better. Admitting these gaps in his argument is completely compatible with admitting that his argument still achieves something: it gives us some reason to believe the conclusion that Hussein desired to produce fissile material for a nuclear bomb. As with many arguments, we understand the argument more fully if we recognize both its accomplishments and also its limits.

  This example also teaches other lessons. Powell’s argument shows that inferences to the best explanation can have important effects even when they are incomplete or worse. Like other arguments, inferences to the best explanation can persuade without justifying. We all need to learn how to evaluate inferences to the best explanation in order to avoid such mistakes and all of their accompanying costs.

  PART III

  HOW NOT TO ARGUE

  10

  HOW TO AVOID FALLACIES

  THERE’S GOOD NEWS AND BAD NEWS. Good arguments are valuable, but bad arguments can be devastating, as we saw in Colin Powell’s testimony to the United Nations. In less extreme cases, bad arguments can mislead us into wasting money on superfluous insurance or unreliable used cars, believing fairytales and delusions, and adopting destructive government programs as well as failing to adopt constructive government programs. These dangers make it crucial to recognize and avoid bad arguments.

  Bad arguments can obviously be intentional or unintentional. Sometimes speakers present arguments that they see as good, even though their arguments are really bad. These are mistakes. In other cases, speakers know that their arguments are bad, but they use them anyway to fool others. These are tricks. The argument can be equally bad in either case. The only difference lies in the arguer’s awareness and intention. It is important to detect fallacies in both cases.

  The idiosyncrasies and variety of bad arguments preclude any complete survey, but many bad arguments do fall into general patterns called fallacies. We already saw several common fallacies, including affirming the consequent and denying the antecedent in deductive arguments plus hasty generalization and overlooking conflicting reference classes in inductive arguments. Of course, false premises can make any argument bad regardless of its form.

  This chapter introduces several more kinds of fallacies that often lead people astray. I will focus on three general groups of fallacies that are especially common.

  WHAT DO YOU MEAN?

  Our definition of arguments revealed not only the purpose and form of arguments but also their material: arguments are made of language. Both premises and conclusions are propositions expressed by declarative sentences in some language. It should come as no surprise, then, that arguments fall apart when language breaks down, just as bridges fall apart when there are cracks in the material out of which they are made.

  Language can crack in many ways, but here the two most common and important defect
s are vagueness and ambiguity. Vagueness occurs when words or sentences are not precise enough for the context. In a scavenger hunt, instructions to find something tall are too vague if players do not know whether they can win by producing a person somewhat above average height. In contrast, ambiguity occurs when a word has two distinct meanings, and it is not clear which meaning the speaker intends. If I promise to meet you next to the bank, then I had better tell you whether I mean the commercial bank or the river bank. A single word can sometimes be both vague and ambiguous, such as when it matters where exactly the river bank ends.

  Double Entendre

  Ambiguity is rampant in newspaper headlines. One of my favorite examples is “Mrs. Gandhi Stoned in Rally in India.”1 Yes, a newspaper actually printed that headline. It can mean either that the crowd threw stones at Mrs. Gandhi or that she took drugs that intoxicated her. You had to read the article to find out. Another favorite is “Police Kill Man With Ax.” Here the issue is not that a single word like “stoned” changes meaning but instead that the man might be “with ax” or the police might be “with ax.” When grammar or syntax creates ambiguity like this, it is called amphiboly. Either kind of ambiguity can produce amusement not only in headlines but also in jokes, such as “I wondered why the Frisbee was getting bigger, and then it hit me.”2

  Such ambiguity is not as innocuous when it ruins arguments. Imagine someone arguing, “My neighbor had a friend for dinner. Anyone who has a friend for dinner is a cannibal. Cannibals should be punished. Therefore, my neighbor should be punished.” This argument is fallacious, but why? Its first premise seems to mean that my neighbor invited a friend over to his house to eat dinner. In contrast, its second premise refers to people who eat friends for dinner. These premises, thus, use different meanings of the phrase “had a friend for dinner.” And if the whole argument sticks with the same meaning in both premises, then one of the premises comes out clearly false. The first premise is not true (I hope) if it means that my neighbor ate a friend for dinner. The second premise is not true if it refers to people who have friends over to their houses for dinner. Thus, the argument fails on either interpretation. This fallacy is called equivocation.

  A more serious example is the widespread argument that homosexuality is unnatural, so it must be immoral. This argument clearly depends on the suppressed premise that what is unnatural is immoral. Adding that extra premise, the argument looks like this: (1) Homosexuality is unnatural. (2) Everything unnatural is immoral. Therefore, (3) homosexuality is immoral.

  The force of this argument depends on the word “unnatural.” What does “unnatural” mean here? It might mean that homosexuals violate laws of nature, but that cannot be correct. Homosexuality is not a miracle, so premise (1) must be false in this sense of “unnatural.” Instead, premise (1) might mean that homosexuality is abnormal or an exception to generalities in nature. This premise is true, simply because homosexuality is statistically uncommon. But now is premise (2) true? What is immoral about being statistically uncommon? It is also uncommon to play the sitar or to remain celibate, but sitar-playing and celibacy are not immoral. On a third interpretation, premise (1) might mean that homosexuality is artificial rather than a product of nature alone, as in food with “all natural” ingredients. But again, what is wrong with that? Some artificial ingredients taste good and are good for you. So premise (2) again comes out false on this interpretation.

  These critics of homosexuality might mean something more sophisticated, such as contrary to evolved purposes. This interpretation is more charitable and plausible. Their idea might be that it is dangerous to go against evolution, such as when someone tries to hammer a nail with his head, since our heads did not evolve to pound nails. This principle plus the added premises that the evolved purpose of sex organs is to produce children and that homosexuals use their sex organs for purposes other than to produce children might seem to support the conclusion that homosexuality is dangerous or immoral.

  How can homosexuals and their allies respond to this argument? First, they can deny that the only evolutionary purpose of sex organs is to produce children. We also evolved in such a way that sex can bring pleasure and express love in heterosexuals as well as homosexuals. There is nothing unnatural about those other purposes. Sex can serve many evolutionary purposes. Second, defenders of homosexuality can deny that it is always dangerous or immoral to use bodily organs apart from their evolved purposes. Our ears did not evolve to hold jewelry, but that does not make it immoral to wear earrings. By the same token, the claim that homosexuals do not use their sex organs for their evolved purposes also would not show anything immoral about homosexuality.

  Finally, the argument might use “unnatural” to mean something like “contrary to God’s plan, intention, or design for nature.” The main problem with this move is to show why defenders of homosexuality should accept premise (1), which now claims that homosexuality is contrary to God’s plan or design. This premise assumes that God exists, that God has a relevant plan, and that homosexuality violates that plan. Many critics of homosexuality accept those assumptions, but their opponents do not. Thus, it is not clear how this argument is supposed to have any force against anyone who did not already agree with its conclusion.

  Overall, then, this argument that homosexuality is immoral because it is unnatural suffers from a central ambiguity. It commits the fallacy of equivocation. This criticism does not end the discussion. Defenders of the argument can still try to respond by delivering a different meaning of “unnatural” that makes its premises true and justified. Alternatively, opponents of homosexuality could shift to a different argument. But they need to do something. The burden is on them. They cannot rely on this simple argument in its present form if it equivocates.

  This example illustrates a pattern of questions that we should ask every time we suspect a fallacy of equivocation. First ask which word seems to change meaning. Then ask which different meanings that word could have. Then specify one of those meanings at each point where that word occurs in the argument. Then ask whether the premises come out true and provide enough reason for the conclusion under that interpretation. If one of these interpretations yields a strong argument, that one meaning is enough for the argument to work. But if none of these interpretations yields a strong argument, then the argument commits the fallacy of equivocation, unless you simply failed to find the meaning that saves the argument.

  Slip Sliding Away

  The second way for language to lack clarity is vagueness. Vagueness is explored in a massive literature in philosophy,3 which discusses such pressing issues as how many grains it takes to make a heap of sand. Vagueness also raises practical issues every day.

  My friends often show up late. Don’t yours? Suppose Maria agreed to meet you around noon for lunch, and she arrives at one second after noon. That is still around noon, isn’t it? What if she arrives two seconds after noon? That’s still around noon, right? Three seconds? Four seconds? You would not accuse her of being late if she arrived thirty seconds after noon, would you? Moreover, one more second cannot make a difference to whether or not she is late. It would be implausible to claim that fifty-nine seconds after noon is not late, but sixty seconds after noon is late. Now we have a paradox: Maria is not late if she arrives one second after noon. One second more cannot make her late if she was not late already. These premises together imply that she cannot ever be late even if she arrives a full hour after noon, since an hour is just a series of one second after another. The problem is that this conclusion is clearly false, because she is definitely late if she arrives an hour after noon.

  This paradox arises partly because we started with the vague term “around noon.” There would be no (or less) paradox if Maria agreed to meet you before noon. But that is the point. Vagueness leads to paradox, and we cannot avoid using vague terms in our everyday speech, so how can we avoid paradox? We can’t.

  Does this paradox matter? It does if we want to understand vagueness theoretica
lly. It also matters practically if Maria is so late that we need to decide whether to complain or leave or order lunch without her. At what time do such actions become justified? I recall sitting for many minutes wondering about this issue.

  No matter how long we wait, we definitely should not reach some conclusions. Several philosophers argue in effect that nobody is ever really late because there is no precise time at which someone becomes late (at least when they promise to arrive around noon). Some also conclude that there is no real difference between being on time and being late. This kind of reasoning is a conceptual slippery slope argument. It makes punctuality unavoidable, because you cannot ever really be late.

  A different kind of slippery slope focuses not on concepts but instead on causal effects. A causal slippery slope argument claims that an otherwise innocuous action will probably lead you down a slippery slope that ends in disaster, so you should not do that first action. If Maria arrives one minute late, and nobody complains, then her minor tardiness might make her more likely to arrive two minutes late the next time, and then three minutes late, and then four minutes late, and so on. Slippery slopes like this lead to bad habits.

  How do we deal with these problems? We draw lines. If Maria starts to show up too late, then we might tell Maria, “If you are not there by 12:15, then I will leave.” We also have to carry out this threat, but there’s nothing wrong with that, if Maria was warned. It might seem problematic to be so arbitrary. However, although it is arbitrary to pick 12:15 instead of 12:14 or 12:16, we still do have reasons to draw some line (How else are we going to get Maria to stop showing up later and later?), and we also have reasons to locate our line within a certain area (after 12:01 and before 1:00). Our reasons for drawing a line between limits solve the practical problem of slippery slope arguments, even if they leave many philosophical issues up in the air.