In the previous chapter, you learned the components of a valid argument and how to test for its soundness. Once you can both empathetically understand an argument and critically evaluate its validity, you can begin to identify the fallacies it contains. Fallacies are failings or weaknesses in your argument. 

It is particularly easy to slip up and commit a fallacy or false fallacy when you have strong feelings about your topic—if a conclusion seems obvious to you, you may be more likely to assume that it is true and to be careless with your evidence or premises. By learning to look for them in your and others’ writing, you can strengthen your ability to evaluate the arguments you make, read, and hear. It is important to realize two things about fallacies: first, fallacious arguments are very, very common and can be quite persuasive, at least to the casual reader or listener. You can find dozens of examples of fallacious reasoning in newspapers, advertisements, and other sources. Second, it is sometimes hard to evaluate whether an argument is fallacious. It requires not only careful examination of the argument but also your own interpretation of that argument. In addition, evaluating an argument is not generally binary but a sliding continuum. The goal is to identify arguments (our own or from others) that lie on the weak side of that continuum and adjust them so that they are stronger. 

There are many kinds of fallacies, here we will just list a few of the most common. 

The Straw Man

One way of making our own arguments stronger is to anticipate and respond in advance to the arguments that an opponent might make. In the straw man fallacy, the arguer sets up a weak version of the opponent’s position and tries to score points by knocking it down. But just as being able to knock down a straw man (like a scarecrow) isn’t very impressive, defeating a watered-down version of your opponent’s argument isn’t very impressive either.

Hasty- or Overgeneralization

Making assumptions about a whole group or range of cases based on a sample that is inadequate (usually because it is atypical or too small). Stereotypes about people (“librarians are shy and smart,” “wealthy people are snobs,” etc.) are a common example of the principle underlying hasty generalization.

False dichotomy

In false dichotomy, the arguer sets up the situation so it looks like there are only two choices. The arguer then eliminates one of the choices, so it seems that we are left with only one option: the one the arguer wanted us to pick in the first place. But often there are really many different options, not just two—and if we thought about them all, we might not be so quick to pick the one the arguer recommends.

Bandwagon

The Latin name of this fallacy, "ad populum," means “to the people.” There are several versions of the bandwagon fallacy, but in all of them, the arguer takes advantage of the desire most people have to be liked and to fit in with others and uses that desire to try to get the audience to accept his or her argument. In one of the most common versions, the arguer tries to convince the audience to do or believe something because everyone else (supposedly) does.

Post Hoc (also called False Cause)

This fallacy gets its name from the Latin phrase “post hoc, ergo propter hoc,” which translates as “after this, therefore because of this.” Assuming that because B comes after A, A caused B. Of course, sometimes one event really does cause another one that comes later—for example, if I register for a class, and my name later appears on the roll, it’s true that the first event caused the one that came later. But sometimes two events that seem related in time aren’t really related as cause and event. That is, correlation isn’t the same thing as causation.

Ad hominem and tu quoque

The ad hominem (“against the person”) and tu quoque (“you, too!”) fallacies focus our attention on people rather than on arguments or evidence. In both of these arguments, the conclusion is usually “You shouldn’t believe So-and-So’s argument.” The reason for not believing So-and-So is that So-and-So is either a bad person (ad hominem) or a hypocrite (tu quoque). In an ad hominem argument, the arguer attacks his or her opponent instead of the opponent’s argument. In a tu quoque argument, the arguer points out that the opponent has actually done the thing he or she is arguing against, and so the opponent’s argument shouldn’t be listened to. Here’s an example: imagine that your parents have explained to you why you shouldn’t smoke, and they’ve given a lot of good reasons—the damage to your health, the cost, and so forth. You reply, “I won’t accept your argument, because you used to smoke when you were my age. You did it, too!” The fact that your parents have done the thing they are condemning has no bearing on the premises they put forward in their argument (smoking harms your health and is very expensive), so your response is fallacious.