What Is a Logical Fallacy? Types, Examples and How to Spot Them
A logical fallacy is an error in reasoning that makes an argument weaker than it looks. Some break the logical form of an argument; others mislead by distracting, misrepresenting or appealing to the wrong kind of reason. This guide defines fallacies, groups them into families, lists the twelve most common in debate, and shows how to call one out fairly.
Updated 2026-11-04
A clear definition
A logical fallacy is a pattern of reasoning that looks like good support for a conclusion but is not. The flaw lies in how the reasons connect to the claim, not only in whether the reasons are true. An argument can contain accurate facts and still be fallacious if those facts do not bear on the conclusion.
Fallacies matter in debate for two reasons. They explain why some arguments persuade when they should not. And they give you a vocabulary for saying exactly what is wrong with a point, which is more useful than saying “that does not sound right.”
Formal and informal fallacies
Philosophers divide fallacies into two broad families.
| Family | What goes wrong | Example |
|---|---|---|
| Formal | The structure of the argument is invalid. The conclusion does not follow even if the premises are true. | If it rains, the pitch is wet. The pitch is wet. So it rained. (Affirming the consequent.) |
| Informal: relevance | The reasons do not bear on the conclusion. | You cannot trust her budget; she is always late. (Ad hominem.) |
| Informal: ambiguity | A word or phrase shifts meaning inside the argument. | A feather is light; what is light cannot be dark; so a feather cannot be dark. (Equivocation.) |
| Informal: weak induction | The evidence is too thin, biased or unrelated to support the claim. | Two of my neighbors were late, so people here are never on time. (Hasty generalization.) |
| Informal: presumption | The argument assumes what it is trying to prove or limits the options unfairly. | It is true because the book says so, and the book is true because it says so. (Circular reasoning.) |
Twelve fallacies every debater should know
This table gives each one in a sentence. Each name links to a full guide in the same series.
| Fallacy | In one line | Example |
|---|---|---|
| Ad hominem | Attacks the person instead of the argument. | “Do not listen to her; she failed her exams.” |
| Straw man | Misrepresents a position, then attacks the distorted version. | “You want less spending, so you want people to starve.” |
| False dilemma | Offers two choices when more exist. | “You are either with us or against us.” |
| Slippery slope | Claims one step will inevitably lead to extreme consequences, without support. | “If we allow this, soon anything will be allowed.” |
| Circular reasoning | Uses the conclusion as a premise. | “He is honest because he never lies.” |
| Hasty generalization | Draws a broad claim from too few cases. | “I met two rude tourists; they are all rude.” |
| Post hoc | Assumes that what follows an event was caused by it. | “I wore my lucky socks and we won.” |
| Appeal to authority | Treats an irrelevant or unsupported authority as proof. | “A celebrity says this diet works.” |
| Red herring | Introduces an irrelevant point to change the subject. | “Why talk about pollution when jobs are at risk?” |
| Appeal to emotion | Uses feeling in place of reasons. | “Think of the children!” with no evidence. |
| Bandwagon | Treats popularity as proof. | “Everyone uses it, so it must be good.” |
| Tu quoque | Dismisses a claim because the speaker does not follow it. | “You say exercise helps, but you never go to the gym.” |
Why fallacies persuade
Most fallacies work because they exploit normal habits of thought. We pay attention to speakers we trust or dislike, so ad hominem works. We favor stories and vivid examples, so hasty generalization works. We like clean choices, so false dilemmas work. And we judge arguments quickly, so a mistake hidden in the structure often goes unnoticed. Knowing why they work makes you less likely to be taken in and less likely to use them by accident.
Watch: Can you outsmart this logical fallacy? (TED-Ed (Alex Gendler)). A short puzzle that shows how a fallacy hides inside a plausible argument.
Fallacies are not always fallacies
Several of these patterns can be reasonable in context. Citing an expert is fine when the expert is relevant and the claim is within their field. Pointing out that a speaker has a financial interest can be relevant to whether to trust their evidence. A slippery slope can be sound if each step is shown to be likely. The test is whether the move gives a good reason for the conclusion. Always ask what the argument claims, then whether the connection holds.
How to call out a fallacy fairly
Saying “that is a straw man!” is not enough, and it can sound like a trick. Follow these four steps.
- Restate what they said, accurately.
- Name the problem in plain words: “That seems to attack a position I did not take.”
- Say why it matters: “So the argument does not address my point.”
- Offer the fix: “If you would like to respond to what I actually said, which is…”
Avoiding fallacies in your own arguments
The best use of this vocabulary is on yourself. After drafting, read each argument and ask these questions.
- Am I attacking an idea or a person?
- Have I represented the other side as they would?
- Are there other options than the two I named?
- Is my example typical, or only convenient?
- Does my evidence connect to my claim?
- Would I accept this reasoning from the other side?
Where to learn more
The Purdue Online Writing Lab and UNC Writing Center both publish short guides to common fallacies with examples. For a deeper treatment, the Internet Encyclopedia of Philosophy and the Stanford Encyclopedia of Philosophy cover the theory. The guides linked above go through the twelve fallacies in this guide one at a time.
Watch: Critical Thinking: Fallacies: Formal and Informal Fallacies (Wireless Philosophy). The difference between errors of form and errors of content.
Frequently asked questions
What is a logical fallacy in simple terms?
A logical fallacy is a mistake in reasoning that makes an argument look stronger than it is. The reasons given do not properly support the conclusion.
What is the difference between a formal and an informal fallacy?
A formal fallacy has an invalid structure, so the conclusion does not follow even if the premises are true. An informal fallacy goes wrong in its content, such as irrelevance, ambiguity or weak evidence.
What are the most common logical fallacies?
Ad hominem, straw man, false dilemma, slippery slope, circular reasoning, hasty generalization, post hoc, appeal to authority, red herring, appeal to emotion, bandwagon and tu quoque.
Does a fallacy mean the conclusion is false?
No. The conclusion may be true. A fallacy shows only that the argument given does not establish it.
How do you point out a fallacy without being rude?
Restate their point fairly, name the problem in plain language, explain why it matters, and invite them to give a better reason.
Sources and further reading
- Logical Fallacies (Purdue Online Writing Lab)
- Fallacies (UNC Writing Center)
- Fallacies (Internet Encyclopedia of Philosophy)
- Fallacies (Stanford Encyclopedia of Philosophy)
- Logical fallacy (Wikipedia)