Rhetoric Moment: Logical fallacies

Making sure your argument holds water

Whenever you write, whatever you write, it's important to know about logical fallacies, arguments that, at first glance, appear sensible – but that don't stand up to closer scrutiny. For that matter, even if you never write anything, knowing how to spot fallacies can help you with the rest of your life.

There are two good reasons to know about logical fallacies. First, you can make your writing stronger by avoiding them; an essay (or blog post) full of fallacies will not be as credible as one in which the reasoning is solid. Second, if you can spot logical fallacies in other material you see, you can develop critical thinking that will allow you to make good decisions. Advertising and politics are full of logical fallacies, and you don't want to fall for them.

Here are some of the logical fallacies that you want to watch out for:

• Hasty generalization. This is jumping to a conclusion when you don't have sufficient evidence to support it. For example, if I ride a city bus once, and the driver is rude to me, I can't logically come to the conclusion that all of the bus drivers in Albuquerque need to improve their manners. It may be that just that one driver is impolite, or it could even be that this driver was just having a bad day.
  
• Slippery slope. This is a subspecies of hasty generalization that uses the reasoning that once a given course of action is started, there is no choice but to continue. Politicians often use this fallacy: "If we legalize medical marijuana, then we will have to legalize it for all purposes, and then we will have to legalize hashish, and then cocaine, and then we will end up as a nation of hopeless drug addicts."
  
• Either/or fallacy (false dichotomy). This is the assumption that there are only two choices, with no room for compromise or gray area between the options, as in "Either you stay in school, graduate, and become rich, or you drop out and are doomed to poverty for the rest of your life." There are other possibilities: Some people don't get a college degree but go into business, find they're good at it, and make millions. Others major in something relatively useless, like English, graduate, and end up teaching in a community college, where they definitely do not get rich!
  
• False analogy. This is comparing two things that do not logically compare to each other, as in, "If we can put a man on the Moon, why can't we cure the common cold?" Space technology has very little to do with biomedical science.
  
• Bandwagon. This is one of my favorites. It's the argument that because everybody is doing something, it must be right. Parents will be familiar with this one: "But, Mom, all of my friends got new Camaros for their sixteenth birthdays!" The standard response, of course, is, "If all of your friends jumped off a cliff, would you do so too?" The bandwagon fallacy is also represented by a couple of bumper stickers that I have seen. One says, "Eat more lamb; 40,000 coyotes can't be wrong." The other, which I have seen primarily on pickup trucks in Texas, follows the same reasoning: "Eat (excrement); sixty billion flies can't be wrong." (I happen to agree with the coyotes and not the flies.)
  
• Non sequitur (does not follow). This fallacy is drawing a conclusion that cannot readily be derived from the information at hand: "Janet would be a great kindergarten teacher because she loves kids." Loving kids doesn't necessarily lead to a person being a good kindergarten teacher; Jeffrey Dahmer loved kids, but he certainly wouldn't have made a good kindergarten teacher – the school officials might start wondering why the class was shrinking.
  
• Begging the question. This fallacy works by ignoring the real question at hand and assuming it has already been answered. For example, the wife says to the husband, "Honey, we need to talk about whether it's time to get a new pickup truck," and the husband responds, "All right, should we get the Ford or the Chevy?"
  
• Ad hominem (to the person). This is another way of sidestepping the real issue by talking about who the opponent is rather than addressing the points the opponent is making: "Bill Clinton supports the North American Free Trade Agreement, but he cheats on his wife."
  
• Guilt by association. This is a subspecies of ad hominem fallacy that argues that because a person is a member of a particular group, we can expect that person to act in a certain way: "The army is a strictly regimented institution; therefore, General Nimrod can't possibly understand the needs of free-spirited civilians." An uglier form of guilt by association is discrimination, when someone with brown or black skin, especially from a high-crime neighborhood, is automatically assumed to be a criminal.
  
• Post hoc (false cause). The Latin phrase post hoc, ergo propter hoc translates as "after this, therefore because of this." It's the assumption that because event B happened after event A, event A must have caused event B: "I washed my pickup truck this morning, and this afternoon it rained." Politicians use this one a lot, and so do advertisers: "I switched to Super-Fresh toothpaste, and now the girls are crazy about me." Well, maybe it was the toothpaste, or maybe the guy just bought a cool new pickup truck and the girls all want to go for a ride.
  
• Circular reasoning. This is the argument that A is true because of B, and B is true because of A. Since the truth of each argument depends on the other, there is no outside evidence to prove the case: "We know that God exists because the Bible says so, and we know the Bible is true because it is the word of God."
  
• Arguing from strength. This is another way of ignoring the real issue or the merits of the argument. Its reasoning is, "I'm bigger and stronger than you are; therefore, I'm right." In Albuquerque, this argument is often expressed at traffic intersections by the drivers of jumbo SUVs: "I don't care what color the light is; I'm bigger than you are, and I'm going through, so get out of my way!"
  
• Appeal to pity. Yet another way of ignoring the actual question at hand, the appeal to pity tries to tug at the audience's heartstrings instead of looking at the facts: "Ladies and gentlemen of the jury, surely you cannot find my client guilty of murdering his mother and father; the poor boy is an orphan!" Conversely, some prosecuting attorneys will argue about how horrible the crime was, instead of looking at evidence that would prove or disprove that the defendant actually committed it.
  
• Appeal to authority. This is calling in an "expert" witness who isn't really an expert. Advertising is full of this type of fallacy. A recent example is the television commercial in which a scantily-clad Paris Hilton washes a car while promoting cheeseburgers. Given her figure, I imagine Paris Hilton is not exactly familiar with cheeseburgers. She's just in the commercial because she's famous and attractive, not because she knows anything about the product.
  
• Arguing from ignorance. This is the argument that, since we haven't seen anything to disprove it, something must be true: "We don't have any evidence that the governor and his buddies took kickbacks; therefore, they must not have taken any." Maybe they did, and maybe they didn't; if we don't have any evidence either way, we need to investigate further.
  

You may notice that there is overlap between some of these fallacies; that's the way rhetoric is sometimes. You may also sometimes run into an argument that contains more than one fallacy. It can be exciting to look at something and say, "Aha! False cause!" or, "Hey, that's a non sequitur." But even more important than being able to put a name to a particular fallacy is just to recognize it for what it is and see that it doesn't logically add up. Beware the politicians and advertisers, and keep your own arguments free of these fallacies that don't hold water.