Below are 25 fallacy-identification questions, arranged from warm-up to LSAT-relevant difficulty, with a full answer key in its own section further down the page. Work through the questions first, keep a running score, then scroll to the key — the separation exists so you can't accidentally read a solution early. For multiple-choice practice with an explanation for each question, try PurrLearn's interactive logical fallacy quiz.
How to take this quiz
Read each argument and describe what's wrong with it before checking the key. The precise Latin label matters less than the diagnosis: on LSAT flaw questions, the answer choices describe the error in plain language ("takes for granted that...", "treats evidence that X as evidence that Y"), so the skill you're training is recognizing and articulating the flaw, not reciting terminology. Give yourself a point whenever your description matches the key's reasoning, even if your label differs. Where taxonomies genuinely vary, the key lists acceptable alternates.
Part 1: Warm-up (questions 1–8)
1. "You can't trust his budget proposal. He's been divorced twice."
2. "Everyone in my office uses this app, so it must be the best one available."
3. "Either we ban all cars from downtown, or the city becomes unlivable."
4. "No one has ever proven ghosts don't exist, so they must be real."
5. "My opponent wants to reduce the defense budget. Clearly she wants to leave us defenseless."
6. "This medicine works — my neighbor took it and felt better the next day."
7. "If we let students retake one exam, soon they'll demand to retake everything, and grades will mean nothing."
8. "This book is reliable because it says so right in its own introduction."
Part 2: Intermediate (questions 9–17)
9. "Crime rose after the new mayor took office. Her policies are obviously causing crime."
10. "A famous physicist endorses this diet, so it must be nutritionally sound."
11. "You claim factory farming is cruel, yet you wear leather shoes. So your argument fails."
12. "The team's average score on the test was 82, so each player on the team must have scored about 82."
13. "Each part of this machine is light, so the whole machine must be light."
14. "We shouldn't accept her tax analysis — think about how much it will upset small business owners."
15. "Sure, I missed the deadline, but have you seen how messy the shared drive is?"
16. "Natural remedies are better because they're natural."
17. "Ninety percent of people surveyed at the marathon expo say running is the best exercise."
Part 3: LSAT-relevant (questions 18–25)
These use the disguise technique of LSAT flaw questions — the error is buried in reasonable-sounding prose — though they are shorter than real stimuli and have no answer choices. Treat them as diagnosis drills, not simulated test items.
18. "In the companies I studied, every highly profitable firm had an open-plan office. Open-plan offices must boost profitability."
19. "The study found no statistically significant link between the supplement and heart health. This proves the supplement has no effect on the heart."
20. "Most novelists are avid readers. Chen is an avid reader, so Chen is probably a novelist."
21. "Freedom of speech must be protected. Therefore, the professor cannot be criticized for her comments."
22. "The senator's argument for the bridge project should be dismissed. Her district would receive most of the construction jobs."
23. "Since it's not illegal, it can't be unethical."
24. "Our sales training works: the reps who completed it outsold the reps who dropped out."
25. "Every argument my critics have raised so far has been flawed, so my theory is correct."
Answer key
1. Ad hominem. The proposal's merits are never addressed; only the proposer's private life is.
2. Bandwagon (ad populum). Popularity is treated as proof of quality.
3. False dilemma. Two options are presented as exhaustive when middle paths exist.
4. Appeal to ignorance. Absence of disproof is treated as proof.
5. Straw man. The position is restated in an exaggerated, easier-to-attack form.
6. Hasty generalization. One case stands in for systematic evidence. Also accepted: anecdotal evidence.
7. Slippery slope. A chain of escalating consequences is asserted without justifying any link.
8. Circular reasoning. The source vouches for itself; the conclusion is smuggled into the premise. Also accepted: begging the question.
9. Post hoc ergo propter hoc. Sequence in time is mistaken for causation.
10. Appeal to inappropriate authority. The expert's authority lies outside the relevant field.
11. Tu quoque. The speaker's inconsistency doesn't refute the claim itself. Also accepted: appeal to hypocrisy, a variant of ad hominem.
12. Fallacy of division. A property of the group (its average) is wrongly transferred to each member — an average of 82 is consistent with no individual scoring near 82.
13. Fallacy of composition. The reverse error: part-level properties projected onto the whole.
14. Appeal to consequences. Unpleasant implications don't make the analysis false. Also accepted: appeal to emotion.
15. Red herring. An irrelevant issue is introduced to redirect attention.
16. Appeal to nature. "Natural" is treated as synonymous with "good" without argument.
17. Biased sample. Surveying people at a marathon expo disproportionately selects respondents who are interested in or favorable toward running; it does not show that every respondent entered with the stated belief. Also accepted: selection bias. Survivorship bias is a subtype of selection bias in which the observed cases are those that passed some survival or selection process while missing cases are overlooked. Practice that narrower pattern in the survivorship bias quiz.
18. Mistaking correlation for causation. Even if the pattern is real, profitability could cause the offices (profitable firms may be better able to afford renovations), or a third factor could drive both. A strong description of either gap earns the point.
19. Appeal to ignorance. Failing to find an effect is not proof of no effect; the study may simply have lacked the power to detect one. Also accepted: misreading a null result.
20. Quantifier reversal. "Most novelists are avid readers" does not tell us what proportion of avid readers are novelists. Because the pool of readers may be much larger than the pool of novelists, Chen's reading habit alone may provide little support for the conclusion. Also accepted: confusion of inverse probabilities or base-rate neglect.
21. Equivocation. "Freedom of speech" shifts from protection against censorship to immunity from criticism.
22. Circumstantial ad hominem. Self-interest may motivate an argument without making it unsound. Also accepted: attacking the source rather than the argument.
23. Conflating legality with morality. Two distinct standards are treated as one. Also accepted: false equivalence.
24. Self-selection bias. Reps motivated enough to finish training may differ from dropouts in ways that also affect sales, so the comparison can't isolate the training's effect.
25. Argument from fallacy. Bad objections don't make a claim true; the theory could be wrong for reasons no critic has raised yet. Also accepted: the fallacy fallacy.
Interpreting your score
Treat the number as a rough self-assessment, not a prediction of test performance.
- 0–8: Review the explanations for Parts 1–2, then practice recognizing the basic patterns in the interactive logical fallacy quiz.
- 9–16: Revisit every missed answer and write one new example of each error in your own words. Retake this quiz after several days.
- 17–21: Your foundation is solid. Concentrate on questions 18–25 and explain each flaw without using its standard label.
- 22–25: Move to arguments with answer choices and more realistic wording, such as the LSAT Logical Reasoning flaw quiz.
Also note where your misses occurred. Errors concentrated in Parts 1–2 suggest that the basic distinctions need review. Errors concentrated in Part 3 suggest that unfamiliar wording or concealed assumptions caused more trouble than terminology did.
Why quizzes can help you learn fallacies
A glossary can introduce labels and definitions, while a quiz asks you to retrieve and apply them to an argument. In this quiz, questions 18–25 may feel harder than questions 1–8 even when the underlying error is familiar because the wording provides fewer obvious cues. Attempting a diagnosis before checking the key can reveal whether you can use a concept without seeing its name first. Quizzes are therefore a useful complement to definitions, though they do not replace careful review or practice with full-length test material.
FAQ
How does this quiz relate to LSAT flaw questions?
LSAT flaw questions present a short argument and ask you to pick the answer choice that describes its error. The patterns drilled here — causal leaps, sampling problems, quantifier reversals like question 20, ad hominem variants, and equivocation — resemble errors those descriptions may target. The transferable skill is articulating the flaw in your own words; real preparation still requires practicing with actual LSAT stimuli and answer choices.
What's the difference between a formal and informal fallacy?
A formal fallacy has an invalid logical structure regardless of the subject matter. An informal fallacy depends on features such as relevance, ambiguity, context, or the quality of the evidence. The boundary is not always classified consistently. Question 20, in particular, is better understood as a probabilistic quantifier reversal or base-rate error than as a clear example of a formal fallacy.
How many logical fallacies should I learn?
Depth beats breadth. Being fast and reliable on the patterns in this quiz — a couple dozen at most — is worth more than passing familiarity with an exhaustive catalogue, because harder questions often reuse familiar errors in new disguises rather than requiring an exotic label.
Can two labels be correct for the same question?
Often, yes. Fallacy taxonomies overlap: tu quoque is commonly treated as a type of ad hominem, while survivorship bias is a type of selection bias. That's why the key lists accepted alternatives and why describing the error matters more than naming it.
Conclusion
You now have 25 worked examples with a separated answer key, alternate labels where taxonomy varies, concrete score ranges, and a diagnosis-first way to assess yourself. Note which part cost you points and retake the quiz after several days. For a test-prep bridge, continue with the LSAT flaw quiz or the GRE Analyze an Argument quiz.