15 Common Logical Fallacies: Errors in Reasoning You Must Avoid
Logical fallacies are errors in reasoning that undermine the validity of arguments. They're everywhere — in political debates, social media arguments, advertising, and everyday conversations. Even intelligent people commit fallacies regularly, often without realizing it. Learning to recognize these flawed patterns of thinking makes you a better thinker, a more discerning consumer of information, and a more effective communicator.
This guide covers the 15 most common logical fallacies, explains why they're problematic, and shows you how to spot them in the wild.
What Is a Logical Fallacy?
A logical fallacy is a flaw in reasoning that makes an argument invalid, even if the conclusion happens to be true. Fallacies can be formal (errors in the logical structure) or informal (errors in the content or context of the argument).
The key thing to understand: a fallacious argument doesn't necessarily mean the conclusion is wrong — it means the reasoning used to reach that conclusion is flawed. The conclusion might be correct for other reasons, but the argument itself fails.
Fallacies of Relevance
These fallacies introduce irrelevant information to distract from the actual argument.
1. Ad Hominem (Attack the Person)
Attacking the person making an argument rather than addressing the argument itself.
Example: "You can't trust Dr. Smith's climate research — she's received funding from environmental groups."
Why it's fallacious: The source of funding doesn't determine whether the research methodology is sound. Attack the data and methods, not the researcher's affiliations.
Variant — Tu Quoque (You Too): Dismissing an argument by pointing out the arguer's hypocrisy. "You say I shouldn't smoke, but you used to smoke!" Whether someone is hypocritical doesn't affect whether their argument is valid.
2. Appeal to Authority (Argumentum ad Verecundiam)
Assuming something is true simply because an authority figure says so.
Example: "This diet must work — it's endorsed by a famous actor."
Why it's fallacious: Expertise in one area doesn't transfer to others. Even genuine experts can be wrong. Evaluate the evidence, not just the source.
Note: Citing experts isn't always fallacious. It becomes fallacious when authority is the only support or when the authority isn't relevant to the topic.
3. Appeal to Emotion
Using emotions — fear, pity, anger, pride — instead of logic and evidence.
Example: "Think of the children!" (without explaining how children are actually affected)
Example: Fear-based advertising showing worst-case scenarios without discussing probability
Why it's fallacious: Emotions can be powerful motivators, but they don't determine truth. A proposition isn't true because it makes you feel a certain way.
4. Appeal to Popularity (Bandwagon Fallacy)
Assuming something is true or good because many people believe it.
Example: "Millions of people use this product, so it must be effective."
Example: "Everyone knows that..."
Why it's fallacious: Popularity doesn't equal truth. Throughout history, the majority has held many beliefs we now know to be false (earth-centered universe, bloodletting as medicine, etc.).
5. Appeal to Tradition
Arguing that something is correct because it's traditional or has always been done that way.
Example: "We've always done it this way, so we shouldn't change."
Why it's fallacious: Longevity doesn't validate an idea. Many long-standing practices have been abandoned as we learned better.
Fallacies of Presumption
These fallacies involve flawed assumptions built into the argument.
6. Straw Man
Misrepresenting an opponent's argument to make it easier to attack.
- Actual position: "We should have sensible gun regulations."
- Straw man: "They want to take away everyone's guns!"
Why it's fallacious: You're attacking an argument your opponent never made. It's intellectually dishonest and avoids engaging with their actual position.
How to spot it: Ask yourself, "Would the person I'm arguing with agree this is their position?"
7. False Dichotomy (False Dilemma)
Presenting only two options when more exist.
Example: "You're either with us or against us."
Example: "Either we ban all cars or accept traffic deaths."
Why it's fallacious: Reality rarely offers only two choices. Most issues have nuanced positions, compromises, and alternative approaches.
8. Slippery Slope
Claiming that one thing will inevitably lead to extreme consequences without justifying the chain of causation.
Example: "If we allow students to redo assignments, next they'll want to redo exams, and soon degrees will be meaningless."
Why it's fallacious: The predicted chain of events isn't demonstrated — it's merely asserted. Each step in the chain needs evidence.
Note: Slippery slope arguments aren't always fallacious if each step can be demonstrated or has historical precedent.
9. Circular Reasoning (Begging the Question)
Using the conclusion as a premise — essentially assuming what you're trying to prove.
Example: "The Bible is true because it's the word of God, and we know it's God's word because the Bible says so."
Example: "Expensive wine tastes better because it costs more."
Why it's fallacious: The argument provides no independent support for the conclusion. It just restates the conclusion as if it were evidence.
10. Loaded Question
Asking a question that contains an unproven assumption.
Example: "Have you stopped cheating on your taxes?" (Assumes you were cheating)
Example: "Why is the government hiding alien technology?" (Assumes a cover-up exists)
Why it's fallacious: Any direct answer accepts the hidden premise. The correct response is to challenge the assumption.
Fallacies of Causation
These fallacies involve errors in identifying cause and effect.
11. Post Hoc Ergo Propter Hoc (After This, Therefore Because of This)
Assuming that because B followed A, A must have caused B.
Example: "I wore my lucky socks and we won the game. The socks caused our victory."
Example: "I started taking supplements and got better. The supplements cured me." (ignoring natural recovery)
Why it's fallacious: Temporal sequence doesn't establish causation. Coincidence, natural cycles, and other factors may explain the outcome.
12. Correlation Does Not Imply Causation
Assuming that because two things correlate, one causes the other.
Example: "Ice cream sales and drowning deaths both increase in summer. Therefore, ice cream causes drowning."
- Direct causation (A causes B)
- Reverse causation (B causes A)
- Common cause (C causes both A and B) — in the example, summer weather causes both
- Coincidence
Other Common Fallacies
13. Red Herring
Introducing an irrelevant topic to divert attention from the original issue.
Example: "The senator shouldn't be questioned about the budget crisis. Look at all the good work he's done for veterans."
Why it's fallacious: Changing the subject doesn't address the original argument. Good work in one area doesn't excuse failures in another.
14. No True Scotsman
Redefining a group to exclude counterexamples rather than accepting them.
- "No Scotsman would do such a thing."
- "But MacDonald did it, and he's Scottish."
- "Well, no true Scotsman would do that."
Why it's fallacious: This protects a claim from refutation by constantly moving the goalposts.
15. Appeal to Ignorance (Argumentum ad Ignorantiam)
Claiming something is true because it hasn't been proven false (or vice versa).
Example: "No one has proven ghosts don't exist, so they must be real."
Why it's fallacious: Absence of evidence isn't evidence of absence (or presence). The burden of proof lies with the person making the claim.
How to Respond to Fallacies
When you encounter a fallacy in conversation or debate:
- Name the fallacy — but gently. Being condescending shuts down productive discussion.
- Explain why it's problematic — help the other person understand the flaw in reasoning.
- Redirect to the actual issue — bring the conversation back to substantive arguments.
Example response:
"That seems like an ad hominem — we're attacking the person rather than their argument. Can we focus on whether the data supports their claim?"
Avoiding Fallacies in Your Own Thinking
The hardest part is catching yourself committing fallacies. Try these practices:
- Steel-man, don't straw-man: Argue against the strongest version of opposing views
- Seek disconfirming evidence: Actively look for information that challenges your beliefs
- Ask "Why?": Trace your reasoning back to its foundations
- Welcome criticism: See challenges to your arguments as opportunities to improve your thinking
- Practice intellectual humility: Accept that you might be wrong
Key Takeaways
- Fallacies are reasoning errors, not necessarily wrong conclusions
- Everyone commits fallacies — the goal is to recognize and correct them
- Context matters: Some arguments that look fallacious (like appeals to authority) are valid when used properly
- Spotting fallacies in others is easy; spotting them in yourself is hard
- The goal isn't to "win" arguments but to find truth
Learning logical fallacies is one of the most valuable critical thinking skills you can develop. It protects you from manipulation, helps you construct stronger arguments, and leads to clearer, more rigorous thinking.
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