Logical Fallacies

When you’re examining an argument, including your own, you want to be on the lookout for gaps in logic, called logical fallacies. In some cases, a speaker or writer may deliberately try to manipulate an audience through a logical fallacy. In other instances, however, a logical fallacy may be the result of unclear thinking. There are many types of fallacies, but here are five very common ones to put on your rhetorical radar.

Ad Hominem. Latin for “to the man,” this fallacy takes place when a speaker or writer attacks the character of his or her opponent rather than the opponent’s ideas. This is a way to shift attention from the issue to the person. For instance, in an argument in favor of the construction of a new school building, someone might point out that a person holding an opposing view was recently fined for speeding or texting while driving. That fact may not be admirable, but it’s unlikely to have any connection to the person’s credibility when it comes to new school construction.

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Bandwagon Appeal. Go with the crowd! That’s essentially the fallacy that occurs when an argument is based on the logic that because a number of people believe something, it must be true or right. So, for instance, you might argue that because millions have used the latest herbal diet supplement, then it must be both safe and effective. Advertisers often use bandwagon appeals in an attempt to persuade consumers that large sales translate into proof of excellence or—perhaps with even faultier logic—that because a celebrity endorses a product, so should you.

Either-Or Fallacy. This fallacy (also known as “false dilemma”) occurs when a speaker or writer makes a veiled threat by reducing a complex issue to two options: either you see it my way or this bad thing will happen. “You’re either with us or you’re with the terrorists” exemplifies the either-or fallacy. Such thinking cuts off the possibility of middle ground or compromise. In addition, this fallacy can artificially limit choices to direct opposites, such as “Either everyone should be allowed to carry a gun or no one should.”

Hasty Generalization. This fallacy occurs when an inference or conclusion is drawn on the basis of insufficient evidence. For instance, if you make an argument that a company is guilty of ageism because your grandfather applied for a job and was not hired, you risk making a hasty generalization. If there is, indeed, a pattern of failing to hire people over a certain age, then you might have a case—but not hiring one person is not a pattern. Note that stereotypes are often formed as a result of hasty generalizations: for example, women are bad drivers; men won’t ask for directions, Midwesterners are overly friendly.

Slippery Slope. This fallacy relies on fear. Also known as the “floodgates fallacy,” the slippery slope occurs when someone argues that if you allow X to occur, Y will surely follow. So, for instance, if you argue that convicted felons should be allowed to vote after they have served their sentences, someone might respond that soon criminals will be running the country. In other words, by doing one thing, you’re on a slippery slope to a far worse and (usually exaggerated) situation.