Logical fallacies: how arguments break, with examples
A field guide to the twenty argument errors you will hear most often, why some of them are only sometimes fallacies, and how to answer them without committing one yourself.
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A logical fallacy is an argument that looks better than it is. The study of them is old: Aristotle's Sophistical Refutations is the first known systematic treatment and lists thirteen types, split into those that depend on language and those that do not (Stanford Encyclopedia of Philosophy). It is also unsettled. The Internet Encyclopedia of Philosophy's partial list contains over two hundred names and states plainly that "the taxonomy of the fallacies is in dispute" (IEP).
That matters in practice. Many items on fallacy lists are not always errors; they are patterns that are fallacious only in certain conditions. A good fallacy guide should help you spot the bad cases without turning every argument into a game of naming Latin terms. For the judgment errors that make these arguments feel persuasive, see cognitive biases.
The 20 fallacies at a glance#
| Fallacy | Latin / other name | The pattern | Example |
|---|---|---|---|
| Straw man | - | Attack a distorted version of the claim | "You want fewer cars downtown? So you want to ban driving." |
| Ad hominem | argumentum ad hominem | Attack the person instead of the argument | "Why listen to her tax plan? She failed accounting." |
| Tu quoque | "you too" | Dismiss criticism because the critic is guilty of it | "You can't tell me to quit smoking; you smoked." |
| False dilemma | black-or-white | Present too few options | "Either we cut the arts budget or the school closes." |
| Slippery slope | - | Claim a small step leads to disaster, without support | "Allow one late assignment and soon nobody submits on time." |
| Post hoc | post hoc ergo propter hoc | B followed A, so A caused B | "I wore my lucky socks and we won." |
| Cum hoc | cum hoc ergo propter hoc | A and B occur together, so one caused the other | "Ice cream sales and drownings rise together, so ice cream is dangerous." |
| Appeal to authority | ad verecundiam | Cite an authority who lacks relevant expertise | "A famous actor says this diet cures disease." |
| Begging the question | petitio principii | The conclusion is assumed in a premise | "This book is reliable because the book says so." |
| No true Scotsman | ad hoc rescue | Redefine the category to dodge a counterexample | "No real fan would leave early." "He did." "Then he wasn't a real fan." |
| Appeal to popularity | ad populum | It's true because many believe it | "Millions use this remedy, so it must work." |
| Appeal to nature | - | Natural means good; artificial means bad | "It's all natural, so it's safe." |
| Appeal to ignorance | ad ignorantiam | Not disproven, so true (or vice versa) | "Nobody has proven ghosts don't exist." |
| Hasty generalisation | - | Broad conclusion from too few cases | "My two neighbours from that city are rude, so everyone there is." |
| Red herring | - | Introduce an irrelevant topic to divert attention | "Why worry about this bug when the competitor has worse ones?" |
| Equivocation | - | Shift the meaning of a word mid-argument | "Evolution is only a theory, and theories are guesses." |
| Composition | - | What's true of parts is true of the whole | "Each player is a star, so the team will be great." |
| Division | - | What's true of the whole is true of the parts | "The company is rich, so every employee is." |
| Loaded question | complex question | A question that presupposes something unproven | "Have you stopped wasting money on that?" |
| Fallacy fallacy | argument from fallacy | The argument is bad, so the conclusion is false | "Your reason was a straw man, so your claim is wrong." |
Straw man#
A straw man replaces an opponent's actual position with a weaker caricature, then knocks that down. The IEP treats caricature as a form of this fallacy (IEP). The fix is the reverse habit, sometimes called steelmanning: restate the other side's view so well that they would agree with your summary before you respond to it.
Straw man: "She thinks we should review the policing budget. So she wants no police at all."
Fair: "She thinks part of the budget should move to mental-health responders. Here's why I think that would or wouldn't work."
Ad hominem (and when it isn't one)#
An ad hominem argument targets the arguer rather than the argument. But the Stanford Encyclopedia notes that John Locke's original use of the term described "not a fallacy but an acceptable mode of argumentation," and that later forms are "sometimes used fairly, and sometimes fallaciously" (SEP). Pointing out that a witness is being paid by one side is relevant to how much you trust their testimony. Pointing out that a mathematician is rude is not relevant to whether her proof is valid.
Tu quoque#
"You too" responds to criticism by noting the critic's hypocrisy. The IEP classifies it as a type of ad hominem (IEP). A parent who smoked can still be right that smoking is harmful; their past makes them inconsistent, not mistaken.
False dilemma#
The IEP describes this as a reasoner who "unfairly presents too few choices," with black-or-white thinking as the two-option version (IEP). Answer it by naming a third option, or by pointing out that the options are not mutually exclusive.
Slippery slope#
Not every slippery slope argument is fallacious. The IEP notes that the form "occurs in both good arguments and faulty arguments," and that its quality depends on how probable each step in the chain is (IEP). The question to ask is: what is the evidence for each link? A precedent that has measurably led to further changes elsewhere is a reason; a chain of "and then, inevitably" is not.
Post hoc and cum hoc#
Both are kinds of false cause. Post hoc infers causation from sequence; cum hoc infers it from co-occurrence, and as the IEP notes, it "doesn't depend on time order" the way post hoc does (IEP). The standard check is to look for a third factor (hot weather drives both ice cream sales and swimming) and for a mechanism. Many of the science myths on this site, such as knuckle cracking causing arthritis, began as post hoc reasoning.
Appeal to authority#
Most appeals to authority are not fallacious. "Much of our knowledge properly comes from listening to authorities," as the IEP puts it; the appeal goes wrong when the authority lacks expertise on the subject, is untrustworthy, conflicts with other authorities, or is misquoted (IEP). A cardiologist on heart disease is a reasonable authority; the same cardiologist on tax law is not.
Begging the question#
In logic, begging the question (petitio principii) means assuming what you set out to prove. The SEP notes that Aristotle described it as asking for the very proposition one is supposed to demonstrate, and that such arguments are often formally valid, which is exactly why they can slip by: they are "attempted proofs that do not transparently display their weakness" (SEP).
In ordinary speech, "begs the question" usually means "raises the question." That everyday use is very common, and we cover the debate in misused idioms and phrases. In writing about arguments, though, use "raises the question" for the everyday sense so readers don't confuse the two.
Ambiguous in an argument essay: "The budget shortfall begs the question of what to cut."
Clear: "The budget shortfall raises the question of what to cut."
No true Scotsman#
When a counterexample appears, the arguer quietly changes the definition so the counterexample no longer counts. The IEP describes it as a kind of ad hoc rescue: redefining the case only to avoid refutation (IEP). Ask the person to state their definition before you test it, and hold them to it.
The fallacy fallacy#
Finding a fallacy in someone's argument shows that the argument fails to support its conclusion. It does not show the conclusion is false. Someone can argue for a true claim badly. Declaring victory because you spotted a fallacy is its own error, and it is particularly common in online debates where fallacy names are thrown around as trump cards.
How to use this list well#
- Name the specific gap (missing evidence, an unstated option, a shifted definition), not just the label.
- Check whether the pattern is actually fallacious here; authority, slippery slope and ad hominem often are not.
- Restate the other side's view fairly before criticising it.
- Apply the same checks to arguments you agree with.
- Remember that a bad argument for a claim is not evidence against the claim.
For more on structuring arguments in writing, Purdue's Online Writing Lab has a concise fallacies reference, and the SEP entry on Aristotle's logic covers where the tradition began.
Frequently asked questions
What is a logical fallacy?
A fallacy is a kind of error in reasoning that tends to look persuasive. The Internet Encyclopedia of Philosophy notes that scholars still dispute the exact definition and taxonomy, and its own partial list runs to more than 200 named fallacies.
Is an appeal to authority always a fallacy?
No. Much of what we know properly comes from experts. An appeal to authority becomes fallacious when the authority lacks expertise on the question, is untrustworthy, is misquoted, or when relevant experts disagree.
What does 'begging the question' really mean?
In logic it means assuming the conclusion in the premises: circular reasoning. In everyday speech it is usually used to mean 'raises the question'. Both uses exist, but in a debate or essay about reasoning, the technical meaning is the one that matters.
If an argument contains a fallacy, is its conclusion false?
Not necessarily. Concluding that a claim is false because someone argued for it badly is itself an error, often called the fallacy fallacy or argument from fallacy. A bad argument fails to support its conclusion; it does not prove the opposite.
What is the difference between a fallacy and a cognitive bias?
A fallacy is a flaw in the structure or content of an argument. A cognitive bias is a systematic tendency in how people judge and decide. Biases often make particular fallacies feel convincing.
Sources
Every factual claim on this page links to one of these. Checked October 2026. See how we source.
- Internet Encyclopedia of Philosophy, Fallacies iep.utm.edu
- Stanford Encyclopedia of Philosophy, Fallacies plato.stanford.edu
- Stanford Encyclopedia of Philosophy, Aristotle's Logic plato.stanford.edu
- Purdue OWL, Logical Fallacies owl.purdue.edu