LSAT flaw questions are the second most common Logical Reasoning question type, appearing approximately 410 times across analyzed tests and making up about 15% of all LR questions. Success on flaw questions requires two skills: spotting the reasoning error in the stimulus and then matching it to the often abstract language of the correct answer choice. This guide covers the most common fallacies, a step-by-step strategy, and how to decode LSAT answer descriptions.
Correlation vs causation. Mistaken reversal and negation. Circular reasoning, equivocation, false dichotomy, ad hominem.
Circular reasoning, equivocation, false dichotomy, ad hominem.
Correlation vs causation. Mistaken reversal and negation. Circular reasoning, equivocation, false dichotomy, ad hominem.
Worked Example
Argument: 'Cities with more police officers have lower crime rates. Therefore, hiring more police officers causes crime to decrease.'
Conclusion doesn't follow from premises. Look for scope shifts or unsupported leaps. Common patterns repeat across tests.
Common patterns repeat across tests.
LSAT answers describe flaws formally. Learn the common translations. Treats sufficient as necessary means mistaken reversal.
| Flaw Name | Plain English | LSAT Abstract Description |
|---|---|---|
| Causal error | Assumes correlation proves causation | Infers a causal relationship from a mere correlation |
| Mistaken reversal | Reverses a conditional | Treats a sufficient condition as a necessary condition |
| Mistaken negation | Negates a conditional incorrectly | Fails to consider that the stated condition may not be necessary |
| Circular reasoning | Conclusion restates a premise | Presumes the truth of what it sets out to prove |
| Equivocation | Uses a word in two different senses | Relies on an ambiguity in a key term |
| False dichotomy | Presents only two options when more exist | Treats two options as exhaustive when they are not |
| Ad hominem | Attacks the person, not the argument | Directs criticism at the person making the argument rather than the argument itself |
| Part-to-whole | Assumes what's true of parts is true of the whole | Infers something about a group from something about its individual members |
| Hasty generalization | Draws a broad conclusion from limited evidence | Draws a general conclusion from an unrepresentative sample |
Treats sufficient as necessary means mistaken reversal.
Name the flaw in plain English first. Eliminate answers describing different flaws. Choose the answer that matches your pre-phrase.
| Step | Action | Purpose |
|---|---|---|
| 1 | Read the question stem — confirm it is a flaw question | Determine your approach before reading the stimulus |
| 2 | Read the stimulus and identify the conclusion | Know what the argument is trying to prove |
| 3 | Identify the premises and the gap | Find where the logic breaks down |
| 4 | Name the flaw in your own words | Pre-phrasing prevents trap answers |
| 5 | Match your pre-phrase to the answer choices | Choose the answer that describes the same flaw |
| 6 | Eliminate answers describing different flaws | Wrong answers often describe real flaws that aren't in THIS argument |
Choose the answer that matches your pre-phrase.
Worked Example
Argument: 'Dr. Martinez claims that the new treatment is ineffective. But Dr. Martinez has received funding from a competing pharmaceutical company. Therefore, the new treatment is likely effective.'
Practice identifying flaws in real stimuli. Build pattern recognition. Focus on the two most common categories.
Focus on the two most common categories.
Flaw questions are the second most common Logical Reasoning question type, appearing approximately 410 times across analyzed tests and making up about 15% of all LR questions. You can expect to see 3 to 5 flaw questions per Logical Reasoning section.
The most frequently tested fallacies include causal reasoning errors, equivocation or ambiguity, circular reasoning, false dichotomy, ad hominem attacks, part-to-whole fallacies, and mistaken reversal of conditional statements.
LSAT flaw answers use formal language to describe reasoning errors. Practice translating common descriptions — for example, 'treats a sufficient condition as necessary' means mistaken reversal, and 'presumes what it sets out to establish' means circular reasoning.
Yes. Identifying the flaw in your own words before reading the answer choices prevents you from being misled by attractive but incorrect descriptions. This pre-phrasing technique is especially effective for flaw questions because it anchors your analysis.