5 Logical Fallacies as Common as a Penny

Do you like a good debate? I bet you do. Oh, you say you don’t? Let me prove you wrong.

The practice of rhetoric goes back to ancient Greece, and it’s been in use ever since. Although we may not take it as seriously as the Greeks did, rhetorical strategies have consistently played a fundamental role in the culture.

Go to any website with a comment thread and you’re bound to find a few knuckleheads engaged in heated debate (I’m using the word “debate” loosely here). We love to defend our point of view. But the problem with the internet and its “anything goes” vibe is that a lot of people eschew logic for the easy attack. Aristotle would not be pleased.

When someone strays from logical reasoning in a debate (or strays from the issue at hand), it’s called a logical fallacy. Many of these fallacies arise when someone feels an emotional connection to an issue, likely arising from personal experience or upbringing. In these cases, it’s easy to let our emotional brain outweigh our logical brain, the latter being what Aristotle thought was the superior tool for persuasion.

A good writer or public speaker should avoid these hasty emotional impulses in a debate. Logical fallacies are cheap, easy, and predictable. Here are five logical fallacies for you to look out for.

1. Ad Hominem: the “No, you’re the puppet!” fallacy.

Latin for “against the man,” this fallacy involves an attack against the person making the argument and not the argument itself. A person’s past or their character traits do not render their current argument invalid, so an ad hominem attack is not logical. It looks like this:

How can we trust this man’s ideas about how to make a marriage last when he’s been through a divorce?

Well, maybe he learned a thing or two from his divorce. Focusing on the person making the argument is a distraction from the argument itself. You avoid attacking an opponent’s character in a logical debate.

2. Slippery Slope: the “Let this happen and the next thing you know…” fallacy.

The slippery slope fallacy plays on a person’s fear of a worst-case-scenario. The formula for the fallacy goes like this: If we let A happen, then Z will happen, therefore we must not let A happen. Sound familiar?

If we let the government restrict our access to machine guns, it’s only a matter of time before they come after our pistols, then our knives, then the old baseball bat we use to protect our homes since they took away our guns. We’ll be defenseless!

Oh, please. That’s not logic; it’s an attempt to stir up hysteria. And, sadly, it works on a lot of people.

3. Black or White: the “You’re either with me or against me” fallacy.

Some people view their whole life through a black or white lens. This means they limit their point of view to polar opposites: Good or bad. Right or wrong. In a way, we’ve been trained for this one-or-the-other mentality. In America, we have a brilliant two-party political system. You either support the person on the right or you support the person on the left. Similarly, we love sporting events where two teams battle it out, and you pick your team and root for them only, discrediting anything good the opponent does.

Yet, when it comes to most issues worthy of debate, there are any number of possibilities, or gray areas, in between the extreme points of view. It isn’t a fallacy, per se, to support the extreme, but it is fallacious to assume there are only two viewpoints.

If you don’t support this war then you don’t support this country.

Yikes. It should be obvious why this is an illogical way of thinking. If you pay attention, almost any issue has conditional “what ifs?” If you take an extreme point of view without paying attention to the spectrum of possibilities, you are guilty of the black or white fallacy.

4. Texas Sharpshooter: the “This one study completely disproves your argument” fallacy.

This fallacy gets its name from a parable of a gunman shooting bullets at the side of a barn. When he’s done, he looks for where there is a cluster of bullet holes close together and draws a target around the holes, creating the appearance that he’s a great shot. When someone focuses on one data-set and ignores the rest, we call that cherry picking, and it’s the basis for the Texas Sharpshooter fallacy:

Melissa pointed to a study that found that 80% of its participants who regularly drank a cup of coffee in the morning had lower blood-pressure than those who did not; therefore, she claimed coffee must be a healthy drink.

The problem with this type of reasoning is that it ignores multiple variables including other lifestyle factors of the participants, additional studies that conflict with these findings, and the occurrence of random chance. The study does not definitively prove coffee is a healthy drink.

5. Bandwagon: the “This is true because 12 of my Facebook friends agree with me” fallacy.

You’re probably familiar with some variation of the adage, “If 100 people say a stupid thing, it is still a stupid thing.” Yet, there is a temptation for a lot of us to believe something just because our peers do. Of course, an idea’s popularity does not make it valid. Appealing to popularity is a fallacy:

Joe assumed that because the majority of his colleagues were in support of Mr. Jones to be the next department head, he must be the most competent candidate for the job, so he also put in his support for Mr. Jones.

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These are just some of the informal logical fallacies we see all the time. If you hope to present a sound argument that others take seriously, you need to first avoid logical fallacies. Focus on sticking to the facts (premises) and using them to make inferences leading to a reasonable end (a conclusion). This is what true rhetoric is all about.