Series hub: This post is one chapter in the critical thinking series. For the full map in one place, read the complete guide.
In one sentence
Fallacies are predictable shortcuts in how arguments are built — naming a few of them helps you locate the weak joint, not win by label.
Why this matters
Feeds reward speed and certainty. Authors (and AI drafts) often skip from a vivid example to a universal rule, attack a person instead of a claim, or treat “many people say” as evidence. If you only feel that something is off, the debate stays emotional. A short vocabulary makes the discomfort specific: which move failed, and what would fix it.
This is not a call to interrupt every conversation with “ad hominem!” Latin tags without charity become their own fallacy — the fallacy fallacy: “they used a weak move, so the conclusion must be false.” Use names as maps, then still check claims, evidence, and interpretation separately (layers guide).
Core ideas
Attack the person, not the claim (ad hominem). “You would say that because of your job” can be relevant to bias — but it does not settle whether the data hold.
Straw man. Refuting a weaker caricature of the view. The fix is steelman: state the strongest version first.
False dilemma. “Either we ban X entirely or we do nothing.” Real options usually include partial, temporary, or conditional policies.
Appeal to popularity or authority. Crowds and experts can be right; popularity and titles are still not substitutes for the underlying evidence.
Slippery slope (unchecked). “If we allow A, we inevitably get Z.” Ask for the mechanism linking steps — some slopes are real, many are rhetoric.
Hasty generalisation. One dramatic story becomes “everyone / always.” Ask for base rates and counterexamples.
Post hoc / correlation treated as cause. After B followed A, A “caused” B. See the companion post on correlation and causation.
You do not need fifty Latin names. These seven cover a large share of everyday media and comment threads.
Practices you can try
- Name → repair. When you spot a move, write one sentence that would make the argument fairer (add the missing option, the mechanism, or the counterexample).
- Two-column skim. Left: claim. Right: “which shortcut, if any?” Leave blank when the reasoning is fine — most text is mixed.
- ThinkLens pass. Paste a heated paragraph into ThinkLens and compare its “potential issues” list with your own labels.
- Fallacy budget. In one day of reading, allow yourself only three labels. Depth beats checklist spam.