5 Common Terms That Double as Logical Fallacies

In simple terms, a logical fallacy is a flaw in reasoning that weakens your argument; you’ve drawn a conclusion based on illogical, irrelevant, deceptive, or otherwise faulty evidence. You’re probably more familiar with fallacies than you think because many of their names double as common expressions—e.g., cherry picking, poisoning the well, and red herring.

In those three cases, the way we casually use the phrase more or less matches how it’s used in logic, philosophy, and debate. Cherry picking is presenting only the evidence that supports your conclusion. Poisoning the well is discrediting a source, so people don’t trust anything they say (all water that flows from a poisoned well is poison, so to speak). And a red herring is information that diverts attention from the matter at hand.

But in other cases, there’s a difference between what a term means in casual conversation and what it means as a logical fallacy. Here are five fascinating examples, from bandwagon to wishful thinking.

1. Bandwagon
2. Begging the question
3. Non sequitur
4. Slippery slope
5. Wishful thinking

Bandwagon

To jump on the bandwagon is “to join in what seems likely to be a successful enterprise,” according to the Oxford English Dictionary. The expression usually carries the negative connotation that the bandwagoner didn’t earn success because they didn’t support the enterprise early enough.

The bandwagon in a bandwagon fallacy also involves a lot of people, but it doesn’t matter when they jump on. Instead, the issue is that you’re using the fact that many people support something—a practice, belief, etc.—as evidence that it’s good or true. It’s also known as an appeal to common belief or an appeal to the masses. For example: Aliens must exist because so many people believe they do. Popularity isn’t proof.

Begging the question

Begging the question is a fallacy whose premise assumes the conclusion is true without actually proving it. For example: You should never skip breakfast because breakfast is an important meal. If you should never skip breakfast, then obviously, it’s important; saying so does nothing to explain why you shouldn’t skip it.

And if you think begging the question is a strange way to describe that phenomenon, you’re correct. Aristotle’s original Greek phrase meant something more like “assuming the original point.” Still, the Latin translation—petitio principii—left room for other interpretations, and begging the question cropped up in English circa the late 1500s.

Outside the world of logic and philosophy, beg the question has two additional definitions. One of them somewhat recalls the notion of assuming the original point: “to ignore a question or issue by assuming it has been answered or settled,” per Merriam-Webster. The other really doesn’t: “to elicit a question logically as a reaction or response.” If a student is caught cheating on a test, for example, it begs the question of how many tests they had previously cheated on. This second sense is so at odds with its Aristotelian source material that some people think it’s just plain wrong—but it’s by far the most common way we use the phrase today.

Non sequitur

We use the term non sequitur—Latin for “it does not follow”—for any statement unrelated to what preceded it. For example, mentioning that your favorite color is blue would be a non sequitur during a conversation about history’s most horrible mutinies.

But non sequitur means something more specific in logic: It’s an inference drawn from premises that don’t actually support it. Consider this example: Spinach leaves are green. Spinach leaves are edible. Therefore, all green leaves are edible. You can’t conclude that all green leaves are edible just because one kind of green leaf is edible—it’s a non sequitur. A logical inference from those two premises would be that some green leaves are edible. 

Slippery slope

A slippery slope fallacy involves arguing against an initial action on the basis that it will lead to a succession of undesirable consequences—but without any significant evidence to support that the series of events will actually occur. The children’s book If You Give a Mouse a Cookie illustrates this surprisingly well (provided that you suspend your disbelief about anthropomorphic mice in general). If you give a mouse a cookie, then he’ll want a glass of milk, and then he’ll want a mirror to make sure he wiped off his milk mustache, and then he’ll realize he needs a haircut, so he’ll ask for scissors, and so forth. Since you don’t want your life to be one long cycle of catering to an entitled mouse, you shouldn’t give him a cookie in the first place. But what evidence do we have that a mouse drinking milk will want a mirror, or that a mouse with a mirror will want a haircut, etc.? 

If you describe something as a slippery slope in any casual context, though, you probably aren’t implying that it’s a fallacious argument. More likely, you mean an action truly will lead you down a bad road. Laughing when a toddler says the f-word, for example, is a slippery slope: They may keep doing it to make you laugh, and before long you’re getting a stern email from their daycare director about inappropriate language.

Wishful thinking

Britannica defines wishful thinking as “an attitude or belief that something you want to happen will happen even though it is not likely or possible.” The Cambridge Dictionary has something very similar: “the imagining or discussion of a very unlikely future event or situation as if it were possible and might one day happen.” Both definitions reflect that we usually mention wishful thinking in reference to the future. It’s wishful thinking to believe that your favorite basketball team, despite its losing record, will make the NBA Finals this year.

But wishful thinking doesn’t have to involve future events: Anything you believe because you want it to be true can be wishful thinking—even if it happened in the past. It’s wishful thinking to still believe your childhood dog was sent to live on an idyllic farm when you’ve known for years that parents just say that to save their kids from the grief of a dead pet.

As a logical fallacy, wishful thinking doesn’t necessarily involve the future, either. In fact, it frequently involves the present: Instead of “I want it to come true, so it will come true,” it’s often a case of “It ought to be true, so it is true.” It’s even sometimes called the “ought-is fallacy” (not to be confused with the is-ought fallacy, wherein you argue that something ought to keep being a certain way because it already is that way). In other words, wishful thinking is using your desire for something to be true as evidence to support that it is true—and that’s not actual evidence. For example: It’s easier to deal with hardship when I know that everything happens for a reason, so everything must happen for a reason.

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