Imagine that somebody tells you, “Elephants are animals. You’re an animal. That makes you an elephant.” It would be easy to tell that this statement is a fallacy—nobody would fall for it. In this chapter, Heinrichs will discuss seven of the most common logical fallacies, the “seven logical sins.”
It’s important to know how to recognize logical fallacies. A person who is able to do so can call out an opponent even if he or she doesn’t know all the specific facts of the argument.
When trying to determine if a statement is logically fallacious or not, you should ask three questions: 1) Does the proof hold up? 2) Am I given the right number of choices? and 3) Does the proof lead to the conclusion? (And you might ask a fourth question, “Who cares?”) If you feel that you sometimes fall for logical fallacies, then you can use these questions to improve your awareness and protect yourself from persuaders, and the “beautiful variety of ways that people cheat, lie, and steal.”
The key to spotting logical fallacies is to compare a statement’s logical steps with the logical steps of a good deductive or inductive argument. Too often, logical fallacies arise because people draw improper conclusions from the evidence, or reduce the evidence to a smaller number of options than are really available.
The first deadly sin is the false comparison. Consider the common food label, “Made with all natural ingredients.” Consumers assume that, since some natural ingredients are healthy, and since a food is made with natural ingredients, then the food must be healthy. But, of course, not all natural things are good. The gist of this logical fallacy is the false assumption that all members of a given group (such as the group of all ingredients that are natural) share a specific trait (being good) when, in fact, many of them don’t.
The underlying problem with the false comparison logical fallacy is a failure of deductive logic: by assuming that all natural things are good, the speaker makes a deductive error, founded on a bad definition of a category.
Another kind of false comparison is the appeal to popularity. Imagine a child asking her parents to drive her to school by claiming that all her friends’ parents drive them to school. This is a false comparison because it uses bad inductive logic to assume that all parents drive their children to school. Or imagine a parent trying to convince her child not to do something by asking, “If everybody jumped off a cliff, would you do it, too?” This is another kind of false comparison, the reductio ad absurdum, in which one sidesteps an example by comparing it with an absurdity (everyone jumping off a bridge).
Appeals to popularity exemplify an error in inductive logic because they generalize from irrelevant examples: just because other kids’ parents drive them to school doesn’t mean that all parents should drive their children to school, too.
Another false comparison is the fallacy of antecedent, assuming that, because something worked in the past, it will continue to work in the future (e.g., “I don’t have to slow down. I haven’t had an accident yet”). There’s also the false analogy—for example, “I’m a successful businessman. Elect me mayor and I’ll run a successful city.” Finally, there’s the unit fallacy, in which people mistake one unit for another—for example, some companies trick consumers by selling detergent in a large box, leading consumers to assume that it’s a better deal than buying a small box (i.e., confusing the size of the box with the price per unit).
The other forms of logical fallacies that Heinrichs discusses here exemplify other errors in the structure of deductive or inductive logic; in particular, they draw the wrong inductive conclusions from limited evidence, or evidence that has been presented in such a way to suggest inaccurate conclusions.
The second logical sin is the bad example. Often, people generalize from a small amount of evidence—for example, if a company hires someone from Yale, and that employee does well, they might be irrationally eager to hire another Yale graduate.
The bad example is another illustration of poor inductive logic, in which the persuader generalizes from limited evidence, perhaps cherry-picking the examples that support their case.
The third logical sin is ignorance as proof. Or, as the former Secretary of Defense Donald Rumsfeld put it, “absence of evidence is not evidence of absence.” A doctor might tell his patient, “You’re in perfect health. The lab tests are negative.” And yet, it’s entirely possible that something is wrong with the patient—just something that the doctor hasn’t tested for.
Ignorance as proof is an especially rich topic, and readers who want to learn more about it would do well to consult Nassim Taleb’s book The Black Swan, or the philosophical writings of Karl Popper.
The fourth logical sin is the tautology, or repeating a premise: i.e., “You can trust our candidate because he’s an honest man.” Another term for tautology is “begging the question” (although many people incorrectly use “begs the question” as if it means “leads us to ask …”).
Tautology is a particularly well-known form of logical fallacy, because it imitates the basic structure of logic (if x, then y) but has no genuine logical content.
The fifth logical sin is the false choice. The essence of this fallacy is that it limits the choices available to the audience. One version of this fallacy is the “many questions” fallacy, commonly used by pollsters (e.g., a pollster asking, “Do you support government financed abortions and a woman’s right to choose?” The fallacy is to assume that voters have to choose between government-financed abortions and being pro-life.) A similar fallacy is the false dilemma—reducing the audience’s choices to two when there are actually many. There’s also the complex cause, in which the persuader isolates one cause for an event when there are many. For example, a lawyer might try to sue a motorcycle helmet company because his client got into an accident while drinking, speeding, and texting—in other words, reducing the accident to only one cause, the malfunctioning helmet.
Offering up a false choice involves engineering the available options in such a way that the audience isn’t aware of some, or most, options. For example, politicians might boil down all choices to two dichotomous options, when there are actually many other options that don’t fall into either category. The complex cause fallacy is beloved of lawyers and “ambulance chasers”—by reducing the many causes of an injury to one or two causes, a savvy lawyer has an easier time suing on behalf of an injured client.
The sixth logical sin is the red herring, named after the escaped prisoners who used pungent herring to throw dogs off their scent. Another trendy name for this logical fallacy is the Chewbacca defense, a reference to a famous episode of the TV show South Park. In the episode, Johnnie Cochran acquits his client by making an argument about Chewbacca that has nothing to do with his case—a satire of the “glove doesn’t fit” argument that Cochran made during the O.J. Simpson trial. In short, the red herring fallacy involves making an irrelevant point that distracts the audience. A related fallacy is the straw man tactic, which involves ignoring one’s opponent’s arguments and attacking a different, more easily refuted argument instead.
Red herring arguments are premised on a “gap” between evidence and conclusion: the conclusion has nothing to do with the evidence, just as Chewbacca has nothing to do with Johnnie Cochran’s client in the South Park episode.
The final logical sin is the wrong ending—extrapolating a false conclusion from the evidence. One version of this fallacy is the slippery slope—suggesting that, if people take a certain action, it will trigger something horrible (for example, politicians are fond of saying that if the government bans assault rifles, then soon we’ll live under a dictatorship). Perhaps the most common wrong ending fallacy is the post hoc ergo propter hoc fallacy—assuming that event A causes event A, simply because A happens before B (for example, a religious fanatic claiming that a hurricane wiped out a city to punish the city for legalizing gay marriage).
These logical fallacies are similar to the bad example, except that instead of using bad evidence, they draw improper conclusions from good, reasonable evidence, often by assuming the most extreme conclusion available. The wrong ending fallacy emphasizes the common feature of all logical fallacies: the disconnect between premises and conclusions. By staying aware of this gap, audiences can catch fallacious reasoning and resist being swayed by it.