In a world flooded with misinformation, disinformation, and a constant stream of persuasion attempts, understanding logical fallacies makes life a lot easier. This knowledge can save you from falling for weak arguments and unfounded conspiracy theories. Crucially, it can also help you formulate stronger arguments of your own. Knowing what these fallacies are and understanding why they’re flawed can improve your thinking, making you impervious to sloppy persuasion while sharpening your analytical skills.
Unfortunately, logical fallacies aren’t always easy to spot. If you’re ready to develop this valuable skill, read on for a deep dive into all things logically fallacious.
What is a logical fallacy?
Logical fallacies are errors in reasoning. Whether an intentional trick or an unintentional error, logical fallacies can make flawed or weak arguments sound convincing. Generally, they come in two kinds:
- Formal fallacies: errors in the form or structure of an argument, such as the conclusion not really following from the premises.
- Informal fallacies: errors in the content of an argument, such as a vague word or a false dilemma.
Informal fallacies are all too common in everyday life. Although there are hundreds in total—the IEP’s partial list includes 231 informal fallacies—most can be grouped into four general categories:
- Fallacies of relevance: Is the reason relevant?
- Fallacies of weak induction: Is the evidence strong enough?
- Fallacies of unwarranted assumption: Is the assumption justified?
- Fallacies of diversion: So what you’re saying is…?
10 Common Logical Fallacies
1. Fallacies of Relevance
When someone relies on fallacies of relevance, they give reasons and evidence that aren’t relevant to a conclusion. Sometimes they’re completely irrelevant, other times they warrant a second look. Since they play off our likes and dislikes, they often go unnoticed.
Two common ones include:
Ad Hominem
Ad hominem fallacies target the person speaking rather than what they say. Three common ones are direct, circumstantial, and tu quoque.
- Direct Ad Hominem: when you attack the speaker’s personality, appearance, voice, or some other character trait.
- Circumstantial Ad Hominem: focus on the person’s circumstances (their past, their job, their associations, etc.) rather than what they say.
- Tu Quoque Ad Hominem: Latin for “you too,” it focuses on the speaker’s hypocrisy rather than the argument they’re presenting.
Tu Quoque Ad Hominem Example:
Fred, lighting up a cigarette, turns to Martha and says, “You shouldn’t smoke cigarettes, they’re bad for your health.” Martha lights up her own cigarette, replying, “Well you’re smoking so they can’t be that bad.”
Tip for spotting ad hominem arguments: If the topic of conversation switches from concepts to characteristics of one of the people involved, that’s a good sign you’ve slipped into ad hominem territory. Ad hominem attacks are often prefaced by the word, “well” (e.g. “well you dropped out of college, so what do you know?”).
Sometimes, ad hominems are warranted—for example, a person can have a conflict of interest that affects their conclusions. However, in general, someone’s appearance, associations, or hypocrisy isn’t enough to discredit their conclusion. A hypocrite can still make a valid point.
Appeal to Emotions
An Appeal to Emotions convinces someone of the merits of an idea or conclusion by eliciting certain emotions in the place of evidence. There are many emotional appeals as there are emotions. However, common ones include:
- Appeal to flattery: You’re so smart, so you know I’m right.
- Appeal to fear: If you don’t act in this way, something terrible will happen.
- Appeal to pity: I broke my leg on the weekend, so I should get an A on the test.
Appeal to Emotions Example:
“If we don’t pass this cybersecurity bill now, the entire country will fall prey to catastrophe!”
Tip for spotting appeals to emotion: If you feel moved by someone’s argument, it’s possible that they’re simply a good orator. However, it’s also possible that they’re using appeals to emotion. So anytime you get emotional when listening to an argument, take a moment to ask yourself why.
Of course, emotions are a part of reasoning, but they shouldn’t be a key factor in whether or not a conclusion is valid. You can feel pity for a student who broke their leg without giving them an A.
2. Fallacies of Weak Induction
Induction is when you draw a conclusion from what you’ve observed. Weak Induction Fallacies are when those observations or experiences aren’t strong enough to support the conclusion.
Four common ones include:
Hasty Generalization
When there’s not enough evidence to draw a reasonable conclusion, that’s a hasty generalization. Typically, this happens when you rely too much on a small sample size.
Hasty Generalization Example
“That restaurant is terrible! I ate breakfast there once and I didn’t enjoy it.”
Tip for spotting hasty generalizations: These arguments tend to feel like a big leap or exaggeration to the listener. They often come packaged with extreme words like “never”, “always”, “worst”, “best”, “terrible”, “amazing”. But the proof backing up these bold claims is flimsy.
There’s no magical number to exactly how much evidence you need to support a claim because claims vary a lot. However, to avoid being too hasty about conclusions, ask clarifying questions about the sample size.
Biased Sample
Instead of not having enough evidence to justify a conclusion, a biased sample relies on biased evidence to support a conclusion. Usually, this means an unrepresentative sample.
Biased Sample Example
“I interviewed 50 psychology students at my university to see what makes them happy. Now, it’s time to write a book about the universal factors of happiness!”
Tip for spotting biased samples: Sampling biases can come in many forms, including self-selection bias (when people with certain characteristics are more likely to sign up for a study), survivorship bias (when successful subjects are more likely to be represented than unsuccessful ones), and undercoverage bias (when certain members of a society are underrepresented in a study). Your best bet for spotting biased samples is to familiarize yourself with all the different forms.
Learning how samples become biased can help you determine whether or not the sample used to support a given conclusion is representative enough.
False Cause
Assuming a causal relationship between two events when there isn’t one necessarily leads to a false cause. Often summed up with the phrase, “correlation isn’t causation,” two common types are:
- Post Hoc, Ergo Propter Hoc (“After this, therefore because of this.”): B came after A, therefore B was caused by A.
- Cum Hoc, Ergo Propter Hoc (“With this, therefore because of this.”): A and B happened together, therefore A caused B.
False Cause Example:
“I was wearing my lucky socks when my team won the game. Therefore, my lucky socks caused the team to win.“
Tip for spotting false cause fallacies: These logical fallacies often arrive in the form of superstitions and conspiracy theories. Of course, they can pop up in all sorts of places, including scientific studies, so always take a moment to think about other factors that could have contributed to an observed outcome.
Although correlation isn’t the same as causation, events that are near each other in space or follow each other in time are often related somehow. The issue is that when you jump too hastily to a conclusion, you could miss the true underlying causes.
Appeal to Ignorance
As Carl Sagan said, “Absence of evidence isn’t evidence of absence.” That, in a pithy nutshell, describes the Appeal to Ignorance fallacy. If claim X lacks evidence, you can’t use that lack of evidence as proof that claim X does or doesn’t exist.
Appeal to Ignorance Example
“I’ve never seen a black swan,” said the 16th-century Londoner. “So, they don’t exist.”
Tip for spotting appeals to ignorance: This fallacy often comes up in arguments with someone essentially saying, “You can’t prove I’m wrong, therefore I’m right.” Remember that not being able to prove something doesn’t necessarily mean the opposite is true.
Note that if a claim is discoverable and there have been considerable attempts to try and discover it, then the Appeal to Ignorance can offer decent support. For example, we can be pretty confident that humans can’t fly unaided.
3. Fallacies of Unwarranted Assumption
Relying on evidence that needs better justification leads to fallacies of unwarranted assumption. Basically, you assume something that’s far from a given.
Two common types are:
False Dichotomy
Also known as a false dilemma, this fallacy only presents a limited amount of options to choose from, when in fact there are many more. False dichotomies reduce a complex issue into a simple and usually inadequate either-or choice.
False Dichotomy Example
“You’re either a patriot or a traitor!”
Tip for spotting false dichotomies: Any time you’re presented with an either/or choice like the one above, consider the two categories and see if you can think of any others that exist.
This argument is structurally sound if there are, in fact, only two choices—such as a person being either dead or alive. However, if there are more than two options, it’s important to question the assumptions being made and explore other possibilities.
Begging the Question
When you assume what you’re trying to prove, you’re begging the question. The premises you use to argue for the truth of a conclusion already assume that the conclusion is true. Also known as circular reasoning, this fallacy can be easy to spot or incredibly subtle.
Begging the Question Example
“Politicians are all untrustworthy.”
“How do you know?”
“Because you can’t trust any of them.”
Tip for spotting circular arguments: You’ll often see the same keywords in the premise as in the conclusion, just swapped around a little.
Instead of begging the question, try to break the circular reasoning loop. Question the assumptions being made and see if there is another source of independent evidence that supports the premises.
4. Fallacies of diversion
Diverting attention away from the argument at hand leads to fallacies of diversion.
Two common ones include:
Strawman
The strawman fallacy is when you exaggerate or misrepresent an argument to make it easier to attack. Just as a man made out of straw would be easier to push over than a real person, it’s far easier to knock down a weak argument than a robust and nuanced one.
Strawman Example
Fred: “We need to reduce pollution and protect the environment for future generations.”
Bert: “So what you’re saying is you want to just stop all industrial progress and take us back to the Stone Age?!”
Tip for spotting a strawman: This fallacy often starts with “So what you’re saying is…” followed by a misrepresentation of what you were saying.
Avoid falling victim to it by identifying the strawman, asking for clarification, and avoiding the all-too-tempting tactic of being a snarky strawman back. Instead, try out a Steel Man argument by giving the strongest possible interpretation of their argument and then responding to that.
Red Herring
When you disregard what the other person says or change the subject, you rely on the red herring fallacy. Also known as a smoke screen, this fallacy is often used to avoid talking about sensitive or controversial topics.
Red Herring Example
Presidential Candidate 1: “We should increase taxes on the wealthy to fund public education.”
Presidential Candidate 2: “Well, it’s important to keep in mind that my opponent has supported policies that harm small businesses. I think small businesses are the backbone of our economy, so we should protect them.”
Tip for spotting red herrings: This style of fallacy often makes you do a little double-take as it comes out of nowhere and doesn’t address the point you raised.
Rather than following it wherever it leads, point out the red herring and ask how it relates to the topic at hand. If it doesn’t relate and is unimportant, drop it. However, if it’s unrelated but important, set it aside to address after they’ve tackled the current point.
Are logical fallacies always wrong?
In short, no. If someone uses a logical fallacy, that doesn’t mean their argument is wrong.
Sometimes fallacies are justified. For example, if a politician is arguing for a policy that benefits a company they have financial ties to, then a circumstantial ad hominem attack may bring to light their conflict of interest. Furthermore, becoming so obsessed with pointing out fallacies that you forget about the topic being discussed is a problem in itself.
That being said, when you recognize a logical fallacy, you should take a moment to pause. Why is the fallacy being used? Is it justified? Once you spot the logical flaw, you can re-evaluate how convincing the argument is. Over time, this will help you build up your analytical rigor and become a better thinker.