The Dirty Dozen: 12 Fallacies Everyone Should Know
A logical fallacy is an error in reasoning that makes an argument invalid — even if it sounds convincing. There are dozens of fallacies, but twelve show up so often that they deserve to be memorised.
Once you know the Dirty Dozen, you'll spot them everywhere: in politics, advertising, social media, and even family arguments.
The Dirty Dozen
1. Ad Hominem (Attack the Person)
"You can't trust her research — she's a vegan!" Attacking the person instead of their argument. The person's character doesn't affect whether their evidence is valid.
2. Straw Man
Misrepresenting someone's argument to make it easier to attack. "You think we should reduce military spending? So you want us to be defenceless?" No — they said reduce, not eliminate.
3. False Dilemma (Either/Or)
"You're either with us or against us." Presents only two options when more exist. Reality is rarely binary.
4. Slippery Slope
"If we allow students to use phones at lunch, next they'll want them in class, and then nobody will learn anything!" Assumes one step inevitably leads to an extreme without evidence for the chain.
5. Appeal to Authority
"A famous actor says this product works!" The authority needs to be relevant. An actor's opinion on medicine is meaningless.
6. Appeal to Popularity (Bandwagon)
"Everyone believes it, so it must be true." Millions of people believed the Earth was flat. Popularity doesn't equal truth.
7. Red Herring
Introducing an irrelevant topic to distract from the argument. "Why worry about climate change when there are homeless people?" Both issues matter; one doesn't cancel the other.
8. Circular Reasoning
"The Bible is true because it says it's the word of God, and God's word is always true." The conclusion is used as a premise. No new evidence is introduced.
9. Hasty Generalisation
"I met two rude French people. All French people are rude." Drawing a broad conclusion from insufficient evidence.
10. Tu Quoque (You Too)
"You say I should exercise more, but YOU don't exercise!" Whether the speaker practises what they preach doesn't affect the truth of their claim.
11. False Cause
"Crime went up after the new park opened. The park caused more crime." Correlation is not causation. Two things happening together doesn't mean one caused the other.
12. Appeal to Nature
"It's natural, so it must be good." Arsenic is natural. Earthquakes are natural. "Natural" doesn't mean safe, good, or desirable.
Tonight's Question
"Can anyone spot a fallacy from today — at school, online, in the news? Which of the Dirty Dozen was it?"
Fallacy Flash Cards
- Create 12 flash cards — one for each fallacy, with the name on front and a family-created example on back.
- Quiz each other: one person reads the example, others guess the fallacy.
- Challenge: each person tries to use three fallacies in a made-up argument. Can others catch all three?
- Keep the cards somewhere visible for a week. See who spots the most fallacies in real life.
Go Further
- Website: yourlogicalfallacyis.com — interactive poster of fallacies with examples.
- Book: Logically Fallacious by Bo Bennett (2012) — comprehensive guide to over 300 fallacies.
- Challenge: Watch a political debate and count the fallacies. You might be surprised how many you find.
- Question: Are there situations where fallacies are acceptable? (e.g., appeal to authority from a genuine expert?)
What We Simplified
- Identifying fallacies isn't always clear-cut. Reasonable people can disagree about whether an argument is fallacious.
- Fallacy accusations can themselves be fallacious. Shouting "That's a straw man!" without explaining why is just as unhelpful as the original fallacy.
- Some "fallacies" have valid versions. Appeal to authority IS valid when the authority has genuine, relevant expertise. The fallacy is in appealing to irrelevant authority.
Sources
- Bennett, B. (2012). Logically Fallacious. eBookIt.
- Walton, D. (2008). Informal Logic: A Pragmatic Approach. 2nd ed. Cambridge University Press.
- Your Logical Fallacy Is. yourlogicalfallacyis.com
- Hamblin, C.L. (1970). Fallacies. Methuen.
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