Logical fallacies: Seven ways to spot a bad argument

I have always been fascinated by persuasion and manipulation. After all, there is only a thin line dividing persuading you to vote for someone, for example, and manipulating you into being a brainless acolyte.

I even did my thesis on brainwashing.

So when I saw this article, I knew I had to publish it.

Logical fallacies: Seven ways to spot a bad argument

By Amanda Ruggeri

When people are trying to persuade you, they sometimes reach for underhand tricks to win an argument. Amanda Ruggeri explains how to identify these logical fallacies. Here’s a summary:

A logical fallacy is a flaw in reasoning that, despite having no bearing at all on a claim's actual merit, can – very confusingly – make the claim sound more convincing.

Using a logical fallacy doesn't necessarily mean someone is wrong. It can, however, indicate either faulty thinking and flawed logic, if used unintentionally, or an attempt to manipulate the truth to be more persuasive, if used deliberately.

Once you know about logical fallacies, you'll see them everywhere. Why does this matter? Because the more practiced you become at spotting them, the better you can be at identifying flaws in people's thinking, and refocusing dialogue back to an argument's merit. You'll also get better at thinking critically yourself.

Here are seven fallacies to look out for.

Some are errors of logic (known as "formal" fallacies), while others are about the misuse of language and evidence ("informal" fallacies) – but the consequence is always a faulty argument.

1. Appeal to ignorance

This is when a lack of evidence is interpreted to mean a claim is real – rather than placing the burden of proof on the person making the claim. It's a fallacy that commonly underlines arguments for conspiracy theories.

Ask one of the estimated 10 million-plus people who believe that lizards run the world about the evidence for their claim, for example, and they might counter, "Well, these lizards are too clever to leave any evidence – that's what makes this situation so dangerous! How can you be sure it's not true?" You might wind up scratching your head, but, hopefully, it's not because you've been persuaded; it's because they've set you the trap of the "appeal to ignorance" fallacy.

2. Ad hominem

This is a fallacy in which a claim is rejected on the basis of an aspect of someone's character, identity, motivations, or even the relationships they have with others. Basically, your down and dirty personal attack.

3. Slippery slope

This is the argument that taking one step, or putting into place one measure, will inevitably lead to more and more drastic measures – like an object sliding down a slippery slope. It's particularly common in debates over policy.

Think of the argument that some opponents of same-sex marriage made against legalizing it. In 2016, researchers at the University of California, Los Angeles found that many people who were against the policy were persuaded by the argument that it would lead to greater sexual promiscuity across society, and threaten their way of life.

4. Strawman

It's misrepresenting the argument of the other side to make it seem more ridiculous, and therefore easy to defeat.

Think of someone who puts forth a nuanced argument that excessive sugar intake may raise the risk of health issues like heart disease. A strawman response would be, "Oh, so what, sugar is killing everyone and should be outlawed? That's absurd!"

This distorts the original argument, making it easier to defeat – a strawman.

One intriguing way to not only fight this tendency, but sharpen your own thinking, is to try a "steelman": you present your opponent's argument in the best possible way (perhaps even better than they have themselves) before you state why you disagree.

5. Appeal to authority

This pernicious argument holds that someone's credentials, fame or reputation alone prove that they must be right.

What makes this a fallacy is when someone buys into an argument solely because of who the person is, rather than because of the argument's evidence or reasoning.

More problematic still is the version known as "appeal to irrelevant authority". Our tendency to believe something because, say, a celebrity states it, even if they have no expertise at all in the topic at hand – a classic tendency in today's influencer-obsessed world.

6. False dichotomy

Presenting a complex scenario as if there are only two either-or, often opposing options, rather than multiple options.

This is the “Either/Or” argument. The best way to counter attack it is to give a third, fourth and even fifth example while calling out the person.

7. Whataboutism

Sometimes considered a type of red herring – a logical fallacy that uses unrelated information to redirect away from the argument's flaws – whataboutism is intended to distract attention. It describes when, normally in response to an accusation or a question, someone responds with their own accusation.

In an argument with a partner, for example, you might say, "It hurt my feelings when you did X." A whataboutism response might be "Well, you never take out the trash!"

Why should you care

Understanding and spotting logical fallacies like this these can be a really useful way to think critically about what you read or watch, and steer (and keep) conversations back on track.

However, because we started this with talk of nuance, let's underscore: if someone uses a logical fallacy, it doesn't necessarily mean their conclusion is incorrect. That, in fact, would be its own fallacy, and perhaps my favorite one of all: the "fallacy fallacy".

Amanda Ruggeri is an award-winning science and features journalist. She posts about expertise, media literacy and more on Instagram at @mandyruggeri.

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