Fallacies and How to Spot Them

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This skill explores different forms of fallacious reasoning, and how to identify them in your own and others’ work.

Fallacious reasoning is reasoning that doesn’t justify its conclusion, but that is (wrongly) presented as if it does. Sometimes, fallacies are deployed deliberately in order to mislead or manipulate people. Sometimes, they occur accidentally or as a result of carelessness. Sometimes, a line of reasoning is expressed in a way that makes it fallacious, if taken literally – but it’s clear enough how this can be remedied by putting things more carefully.

Learning to spot fallacies is useful partly because fallacious ways of thinking can be seductive or appealing – and partly because some fallacies are so commonplace that, in everyday life, we often forget they don’t actually justify the belief they’re claimed to justify.

An ad hominem fallacy, for example, occurs when we dismiss something based entirely upon who is saying it, rather than based upon what they’re saying. This is fallacious because – while the identity of someone making a claim may be valuable information – it’s dangerous to rely on ‘whatever person X says cannot be trusted’ as a general rule. Such a refusal of reasoned engagement is likely to lead to other people refusing reasoned engagement in turn; and it promotes the view that how we feel about particular people matters more than seeking either to understand or investigate their claims.

As we’ll see, fallacies tend to offer simplifications or generalisations that present complex situations as if they were straightforward. Another everyday example is the fallacy known as ‘an appeal to popularity’, which suggests that anything that is popular must also be good – something that may or may not be true of some situations, but that doesn’t work as a general rule.

After discussing what faulty reasoning entails in general, we will look at two particular classes of fallacy: formal and informal fallacies.

Informal fallacies rely on misleading or inaccurate claims that need to be identified via a consideration of the details or context of an argument. Formal fallacies, by contrast, are flaws in deductive logic and can thus be identified purely by looking at the form of an argument. We’ll examine and name several different types of fallacies in each category, with an emphasis on practical examples – and what it means to push back against fallacious thinking by using comparable examples.

Using comparable examples is one of the most useful everyday ways of identifying and pushing back against fallacious thinking. It entails re-using the form of a fallacious argument in a new context. For example, the fallacy underlying the mistaken argument ‘you can’t prove she is innocent, therefore she must be guilty’ can be highlighted by comparing it to the (more obviously absurd) claim ‘you can’t prove she isn’t secretly a wizard, therefore she must be secretly a wizard’.

While identifying fallacies isn’t a sure guide to reasonable thinking, it can offer some memorable insights into common sources of unreasonable or unjustified thinking – and help you both to avoid these in your own work and to become less likely to accept them in others’.

Pause for Thought

Can you think of a particularly appealing version of one of the fallacies outlined above? What about an obviously absurd example of the same fallacy?

Suggested Readings

  • For a truly in-depth guide to the history of thinking about fallacies – and their various forms – the Stanford Encyclopedia of Philosophy is a rich online resource.
  • My textbook Critical Thinking (SAGE) offers a detailed guide to the fallacies outlined in this skill; I’ve also produced a potted video guide to fallacies on YouTube
  • When it comes to opposing bad reasoning, there’s a handy free online guide to arguing against common fallacies at the Future Learn website
  • Ali Almossawi’s Illustrated Book of Bad Arguments is a charming, accessible guide to fallacious reasoning, and can be found online at bookofbadarguments.com
  • For a lively visual guide to fallacies, and some other engaging resources, the Your Logical Fallacy Is website is worth a visit