Identify a Flaw: Master LSAT Logical Reasoning Flaw Questions
Learn expert strategies to identify logical fallacies, spot reasoning errors, and ace flaw questions on the LSAT Logical Reasoning section with official examples, common flaw patterns, and proven techniques from the Law School Admission Council.
Identify a flaw questions, also called flaw in reasoning questions or descriptive weakening questions, are among the most common and important question types in the LSAT Logical Reasoning section. These questions present a flawed argument and ask you to identify precisely how the reasoning is defective. Rather than weakening or strengthening the argument, your task is to describe the specific logical error the author commits.
The Law School Admission Council (LSAC) includes flaw questions to assess a critical legal skill: recognizing faulty reasoning patterns. Attorneys must constantly evaluate arguments from opposing counsel, witnesses, and clients, identifying weaknesses in logic before they can construct effective counterarguments. Spotting flawed reasoning is foundational to legal analysis and advocacy.
📊 Question Frequency
Flaw questions typically appear 4-6 times per Logical Reasoning section, making them one of the most frequent question types on the LSAT. Across both scored LR sections, you can expect 8-12 total flaw questions. Combined with their high learnability through pattern recognition, mastering flaw questions offers exceptional return on study investment.
What Are Identify a Flaw Questions
Flaw questions present an argument with a logical error in its reasoning structure. The premises may be true, but the conclusion doesn't necessarily follow from them due to a gap, assumption, or logical mistake. Your task is selecting the answer choice that best describes this specific reasoning error.
🔍 Common Question Stems
Standard Identification Stems:
- "The reasoning in the argument is flawed because..."
- "Which one of the following most accurately describes a flaw in the argument's reasoning?"
- "The argument is most vulnerable to criticism on the grounds that it..."
- "A reasoning error in the argument is that the argument..."
- "The argument is questionable because it..."
Vulnerability Stems:
- "The argument is vulnerable to criticism because it fails to..."
- "A weakness in the reasoning is that it..."
- "The argument's reasoning is most susceptible to the criticism that it..."
What Makes Reasoning Flawed
An argument is flawed when its conclusion doesn't necessarily follow from its premises, even if the premises are true. This happens when:
- The argument makes unwarranted assumptions that bridge gaps between evidence and conclusion
- The argument ignores alternative explanations or relevant possibilities
- The argument misapplies logical relationships (confusing sufficient with necessary, correlation with causation)
- The argument overgeneralizes from limited evidence or applies evidence too broadly
- The argument attacks the source rather than the claim or commits other irrelevant reasoning
Premises + Logical Gap = Conclusion
Your task: Identify and describe the specific logical gap
Official LSAC-Style Example Analysis
Let's examine an LSAT-style flaw question to understand the identification process:
📚 Flaw Question Example
Argument: Studies show that people who drink coffee regularly have a lower risk of developing Parkinson's disease than people who do not drink coffee. Therefore, drinking coffee must protect against Parkinson's disease.
The reasoning in the argument is flawed because the argument:
- Fails to consider that people who don't drink coffee might engage in other behaviors that increase their risk of Parkinson's disease
- Takes a correlation as evidence of causation
- Fails to address why people who drink coffee have lower rates of Parkinson's disease
- Assumes that what is true of a group is necessarily true of each individual in that group
- Draws a conclusion based on a sample that is likely unrepresentative of the population as a whole
Step-by-Step Analysis
Step 1: Identify the Conclusion
Conclusion: Drinking coffee must protect against Parkinson's disease
Indicator: "Therefore" signals the conclusion
Strength: "Must protect" is a strong causal claim
Step 2: Identify the Premises
Premise: Studies show coffee drinkers have lower risk of Parkinson's than non-coffee drinkers
Type of Evidence: Correlation—two things occur together
Step 3: Identify the Logical Gap
The Reasoning Error
What the evidence shows: Coffee drinking and lower Parkinson's risk are associated (correlation)
What the conclusion claims: Coffee drinking causes lower Parkinson's risk (causation)
The gap: The argument moves from correlation to causation without justification
Flaw Type: Correlation ≠ Causation
Step 4: Evaluate Each Answer
(A) Fails to consider other behaviors:
This points to an alternative explanation for the correlation, which would indeed weaken the causal claim. However, it doesn't precisely describe the core logical error—the unjustified leap from correlation to causation. This is close but not the best description.
(B) Takes correlation as evidence of causation:
This precisely describes the flaw. The argument observes that two things occur together (correlation: coffee drinking and lower Parkinson's rates) and concludes that one causes the other (causation: coffee protects against Parkinson's). This is the classic correlation-causation confusion. ✓ CORRECT
(C) Fails to address why coffee drinkers have lower rates:
This describes what the argument doesn't do, but an argument isn't necessarily flawed for failing to explain a mechanism. The flaw is concluding causation from mere correlation, not failing to explain the causal mechanism. Incorrect.
(D) Assumes what's true of a group applies to individuals:
This describes a part-whole flaw or composition fallacy. The argument doesn't make claims about individual coffee drinkers—it makes a general claim about the group. This isn't the flaw present. Incorrect.
(E) Draws conclusion from unrepresentative sample:
The argument doesn't mention sample size or representativeness. This would be relevant if we questioned whether the studies were representative, but that's not the logical error being committed. Incorrect.
✓ Why (B) is Best
Answer (B) captures the precise logical error: moving from correlation (observational association) to causation (one thing causes another) without justification. This is among the most common flaws on the LSAT. The evidence supports correlation; the conclusion asserts causation. That unjustified logical leap is the flaw.
Key Insight: The best answer describes the specific reasoning error, not just things the argument didn't consider or evidence it didn't provide.
The Most Common Logical Flaws on the LSAT
While LSAT arguments can be flawed in countless ways, certain patterns appear repeatedly. Mastering these common flaws accelerates your ability to identify reasoning errors:
1. Correlation vs. Causation
Flaw Description
Error: Concludes that because two things occur together, one must cause the other
Symbolic Form: A correlates with B → A causes B
Why It's Flawed: Correlation can exist without causation. Possibilities include: (1) B causes A (reverse causation), (2) C causes both A and B (common cause), (3) pure coincidence, (4) complex multi-factor relationships.
Example: "Ice cream sales and drowning deaths both increase in summer, so ice cream sales cause drowning." The flaw: both are caused by hot weather (common cause).
Answer Language: "mistakes correlation for causation," "treats a correlation as evidence of causation," "infers a causal relationship from mere association"
2. Sufficient vs. Necessary Conditions
Flaw Description
Error: Confuses what's sufficient (enough) to guarantee something with what's necessary (required) for it
Symbolic Form: A → B treated as B → A
Why It's Flawed: If A is sufficient for B (A → B), you can't conclude B is sufficient for A. Example: Being a dog is sufficient for being a mammal, but being a mammal isn't sufficient for being a dog.
Example: "All scholarship recipients have high grades. Sarah has high grades, so she must be a scholarship recipient." The flaw: high grades are necessary for the scholarship, not sufficient.
Answer Language: "mistakes a condition necessary for X with one sufficient for X," "treats a requirement as a guarantee," "confuses sufficient and necessary conditions"
3. Unrepresentative Sample
Flaw Description
Error: Draws a general conclusion from a sample that's too small, biased, or otherwise unrepresentative of the whole population
Why It's Flawed: If your sample differs systematically from the population you're generalizing about, your conclusion may not hold for the broader group.
Example: "I surveyed students at Harvard Law School, and 90% plan to work in corporate law. Therefore, most law students nationwide plan to work in corporate law." The flaw: Harvard Law students may not represent all law students.
Answer Language: "generalizes from an unrepresentative sample," "draws a conclusion from a sample likely to be biased," "bases a general claim on evidence from a special case"
4. Part vs. Whole (Composition/Division)
Flaw Description
Error: Assumes what's true of parts must be true of the whole (composition), or what's true of the whole must be true of each part (division)
Why It's Flawed: Properties can differ between parts and wholes. A lightweight brick isn't proof that a building made of those bricks is lightweight.
Example (Composition): "Each player on the team is talented, so the team must be talented." The flaw: talented individuals don't guarantee team coordination.
Example (Division): "The company is profitable, so each department must be profitable." The flaw: some departments may operate at a loss.
Answer Language: "assumes what is true of the whole must be true of each part," "infers a characteristic of parts from a characteristic of the whole," "fallacy of composition/division"
5. Circular Reasoning (Begging the Question)
Flaw Description
Error: The conclusion is essentially a restatement of a premise, or the premise assumes the conclusion is true
Symbolic Form: A → A
Why It's Flawed: It's not reasoning at all—you're assuming what you're trying to prove. "I'm trustworthy because I'm honest, and I'm honest because I'm trustworthy" proves nothing.
Example: "The death penalty is just because criminals deserve to die. We know criminals deserve to die because the death penalty is just." The conclusion restates the premise.
Answer Language: "presupposes what it sets out to prove," "takes for granted the very claim it's trying to establish," "circular reasoning," "begs the question"
6. Possible vs. Certain (Strength of Conclusion)
Flaw Description
Error: Concludes something is certain or definite based on evidence that only shows it's possible or probable
Why It's Flawed: Evidence supporting "might happen" or "probably will happen" doesn't justify "definitely will happen."
Example: "Economists predict a recession is possible next year. Therefore, there will definitely be a recession next year." The flaw: possible ≠ certain.
Answer Language: "treats a possibility as a certainty," "draws a definite conclusion from evidence supporting only probability," "mistakes what could be true for what must be true"
7. Ad Hominem (Attacking the Source)
Flaw Description
Error: Rejects a claim based on characteristics of the person making it rather than the merits of the claim itself
Why It's Flawed: The truth or validity of a claim doesn't depend on who says it. Even unreliable people can make true statements.
Example: "Senator Jones argues for tax reform, but she's been involved in scandals. Therefore, tax reform is a bad idea." The flaw: Jones's character doesn't determine tax reform's merits.
Answer Language: "rejects a claim by attacking the source rather than addressing the claim itself," "ad hominem reasoning," "dismisses an argument based on the arguer's characteristics"
8. False Dilemma (Either/Or)
Flaw Description
Error: Presents only two options when additional alternatives exist, then eliminates one to conclude the other must be true
Symbolic Form: Either A or B. Not A. Therefore B. (when C, D, E also exist)
Why It's Flawed: The reasoning is only valid if the two options genuinely exhaust all possibilities. If other options exist, the conclusion doesn't follow.
Example: "Either we ban all cars or air pollution will worsen. We won't ban all cars, so air pollution will worsen." The flaw: other options exist (electric cars, emissions standards, public transit).
Answer Language: "fails to consider alternatives," "presents a false dichotomy," "overlooks other options," "assumes only two possibilities exist"
Quick Reference: Common LSAT Flaws
| Flaw Type | Description | Common Answer Language |
|---|---|---|
| Correlation → Causation | Treats correlation as proof of causal relationship | "mistakes correlation for causation" |
| Sufficient ↔ Necessary | Confuses conditions that guarantee with conditions that are required | "mistakes necessary for sufficient" |
| Unrepresentative Sample | Generalizes from biased or too-small sample | "generalizes from unrepresentative sample" |
| Part vs. Whole | Assumes characteristics transfer between parts and wholes | "assumes what's true of parts is true of whole" |
| Circular Reasoning | Conclusion restates or assumes the premise | "presupposes what it sets out to prove" |
| Possible → Certain | Draws definite conclusion from probable evidence | "treats possibility as certainty" |
| Ad Hominem | Attacks source rather than claim | "rejects claim by attacking the source" |
| False Dilemma | Presents two options when more exist | "fails to consider alternatives" |
| Equivocation | Uses a term with shifting meanings | "uses a key term in two different senses" |
| Appeal to Authority | Accepts claim because authority says it (when authority isn't expert in that domain) | "appeals to inappropriate authority" |
| Absence of Evidence | Treats lack of evidence for X as evidence against X | "absence of evidence taken as evidence of absence" |
| Percent vs. Amount | Confuses relative proportions with absolute numbers | "confuses relative with absolute values" |
Step-by-Step Strategy for Flaw Questions
Success requires systematic analysis of the argument's structure and precise identification of the reasoning error:
Read the Question Stem First
Confirm it's a flaw question. Knowing you're looking for a reasoning error focuses your reading. You're not evaluating whether the conclusion is true, but whether the reasoning is valid.
Identify the Conclusion
Find the main claim the argument is trying to establish. Look for conclusion indicators: "therefore," "thus," "so," "consequently," "it follows that." The conclusion is what the author wants you to believe.
Identify the Premises
Find the evidence offered in support of the conclusion. Look for premise indicators: "because," "since," "given that," "the reason is." Separate background information and opposing views from actual premises.
Identify the Gap or Assumption
What must be true for the conclusion to follow from the premises? What's the author assuming? Where's the logical leap? Common gaps: correlation to causation, sufficient to necessary, sample to population, parts to whole.
Articulate the Flaw in Your Own Words
Before reading answer choices, describe the reasoning error yourself: "The argument assumes causation from correlation" or "The argument treats a necessary condition as sufficient." This prediction anchors your evaluation.
Evaluate Each Answer Choice
Ask two questions: (1) Did the author actually do what this answer describes? (2) If yes, is that a problem for the argument? Both must be true for the answer to be correct.
Eliminate Wrong Answers
Remove answers that: describe something the author didn't do, describe something that isn't actually a flaw, are too vague or general, describe a different argument entirely, or use technical terminology incorrectly.
⚠️ The "Sounds Smart" Trap
Wrong answers often use impressive logical terminology but describe things the argument didn't do. Don't be seduced by sophisticated language. Always verify: did the argument actually commit this error? An answer can be a valid logical flaw in general but still be wrong if that's not the flaw in this specific argument.
Common Wrong Answer Patterns in Flaw Questions
Recognizing predictable wrong answer patterns accelerates elimination:
1. Describes Something the Author Didn't Do
The answer describes a valid logical flaw, but the argument doesn't commit that particular error. Always check: did the argument actually do this?
2. Describes Something That Isn't Actually a Flaw
The answer accurately describes what the author did, but that thing isn't problematic. The author did X, but X isn't a reasoning error in this context.
3. Too Vague or General
The answer could apply to almost any flawed argument ("fails to consider all possibilities," "relies on questionable evidence"). The correct answer specifies the particular flaw.
4. Confuses Necessary and Sufficient in the Answer
The answer itself reverses necessary and sufficient, describing the flaw incorrectly. For example, if the argument mistakes necessary for sufficient, a wrong answer might say it mistakes sufficient for necessary.
5. Attributes Unstated Claims to the Author
The answer describes a flaw based on something the author never said or implied. Don't attribute positions to the author beyond what's actually stated.
6. Uses Technical Terms Incorrectly
The answer misuses logical terminology (ad hominem, straw man, etc.) in ways that don't match the actual argument.
7. Describes the Argument's Conclusion, Not Its Flaw
The answer criticizes what the author concludes rather than how the author reasons to that conclusion. Flaw questions ask about reasoning, not about whether conclusions are true.
✓ The Two-Question Test
For every answer choice, ask:
- Did the author actually do this? Check the argument. If not, eliminate immediately.
- If yes, is this a problem? Does this make the reasoning faulty? If not, eliminate.
Only answers that pass both tests can be correct. This systematic approach prevents being fooled by sophisticated-sounding but irrelevant answers.
Advanced Techniques for Flaw Questions
Technique 1: Pattern Recognition Through Categorization
As you practice, categorize each flaw question by type (correlation-causation, sufficient-necessary, sample, etc.). Build a mental catalog of how each flaw appears in arguments and how answers describe it. After 50-75 flaw questions, you'll recognize patterns instantly.
Technique 2: The Assumption-Flaw Connection
Every flaw corresponds to an assumption. If you identify the assumption (the gap between premises and conclusion), you've identified the flaw—the argument assumes something without justification. Practice moving fluidly between "What does this assume?" and "What's the flaw?"
Flaw = Unjustified Assumption
The argument's flaw is that it assumes X without providing evidence for X
Technique 3: The Reversal Test
For sufficient-necessary confusion, test the conditional logic both ways. If the argument says A → B and concludes B → A, you've found the flaw. Practice diagramming to spot reversals quickly.
Technique 4: Alternative Explanation Thinking
For correlation-causation flaws, actively generate alternative explanations: reverse causation, common cause, coincidence. If multiple explanations fit the evidence equally well, the argument's causal conclusion is unjustified.
Technique 5: Scope Comparison
Compare the scope of premises with the scope of the conclusion. Evidence about "some" leading to a conclusion about "all," or evidence about "usually" leading to "always," signals an overgeneralization flaw.
Scope Analysis Example
Premise Scope: "Studies show that many meditation practitioners report lower stress."
Conclusion Scope: "Meditation definitely reduces stress for everyone."
Flaw: Scope shift from "many report" (some, subjective) to "definitely reduces for everyone" (all, objective). The evidence doesn't support the conclusion's broad, definitive scope.
Technique 6: The "So What?" Test
After reading the premises, ask "So what?" Does the conclusion actually follow? If your reaction is "That doesn't necessarily mean..." you've likely spotted the gap. Articulate what would need to be true for the conclusion to follow—that's the unjustified assumption.
How to Practice Flaw Questions
Effective practice builds pattern recognition and strengthens your ability to articulate flaws precisely:
Phase 1: Flaw Pattern Foundation (Week 1-2)
- Study the common flaw types: Learn the 8-10 most frequent flaws thoroughly
- Work 20-30 flaw questions untimed from official PrepTests
- For each question: Identify conclusion, premises, gap, flaw type, and why wrong answers fail
- Create flashcards: Flaw type on one side, description and common answer language on the other
- Build a flaw journal: Track each flaw, note which ones you miss, identify your weak spots
Phase 2: Speed and Precision (Week 3-4)
- Practice articulating flaws: Before reading answers, describe the flaw in one sentence
- Focus on correlation-causation and sufficient-necessary: These two account for 30-40% of flaw questions
- Work on wrong answer elimination: Practice the two-question test systematically
- Begin timing: Start at 90 seconds per question
- Review extensively: For every question, understand why four answers are wrong, not just why one is right
Phase 3: Integration and Mastery (Week 5+)
- Complete full Logical Reasoning sections: Practice flaw questions alongside other types
- Target 60-75 seconds per question: Flaw questions should be quick once you recognize the pattern
- Aim for 90%+ accuracy: Flaw questions are among the most learnable question types
- Practice explaining flaws aloud: This solidifies your understanding and mimics test conditions
- Do untimed review sessions: Periodically return to challenging flaw questions to deepen mastery
📈 Mastery Indicators
- You recognize flaw types within seconds of reading the argument
- You can articulate the flaw in your own words before reading answers
- You eliminate 2-3 wrong answers quickly using the two-question test
- You achieve 90%+ accuracy consistently on flaw questions
- You complete flaw questions in 60-75 seconds reliably
- You can explain why each wrong answer is wrong, not just why the right answer is right
Official LSAT Resources for Flaw Questions
Use only official materials from the Law School Admission Council (LSAC) and authorized partners for practice:
Primary Official Resources
- LSAC Official Logical Reasoning Overview - Official information about Logical Reasoning section and skills tested, including identifying flaws in arguments
- LSAC Official LSAT Prep - Official preparation materials and study resources
- Official LSAT PrepTests - Published PrepTests with real, previously administered questions
- Khan Academy LSAT Prep - Free official LSAT preparation in partnership with LSAC
- LSAC Sample Questions - Free sample Logical Reasoning questions with explanations
Recommended PrepTest Range
For current question styles and difficulty:
- PrepTests 62-94: Most recent exams with current format and flaw patterns
- SuperPrep I & II: Official books with comprehensive explanations of reasoning errors
- 10 Actual, Official LSAT PrepTests: Collections of authentic exams
- PrepTests 52+: Modern LSAT format
📚 LSAC's SuperPrep Books
The SuperPrep and SuperPrep II books are particularly valuable for flaw questions. They include detailed explanations that walk through exactly what makes each argument flawed and why each answer choice is right or wrong. These explanations teach you to think like LSAC question writers, helping you recognize flaw patterns and answer construction strategies.
⚠️ Official Materials Only for Practice
Always practice with official LSAC questions. Flaw questions require precise argument construction and exact flaw types. Unofficial questions may not replicate LSAC's logical precision, leading to bad pattern recognition habits. Use commercial resources for strategy instruction, but apply those strategies exclusively to official LSAC materials.
Frequently Asked Questions
Test Day Strategy for Flaw Questions
✓ Quick Reference Checklist
- Confirm it's a flaw question from the stem
- Read the argument carefully and identify conclusion and premises
- Identify the gap between premises and conclusion
- Articulate the flaw in your own words
- Match your prediction to the answer choices
- Apply the two-question test: Did the author do this? Is it a problem?
- Eliminate wrong answers systematically
- Select the answer that precisely describes the reasoning error
Time Management
⏱️ Optimal Timing
- Simple flaws (correlation-causation, sufficient-necessary): 60-70 seconds
- Moderate flaws (sample, part-whole, scope shifts): 70-80 seconds
- Complex flaws (multiple gaps, conditional chains): 80-90 seconds
Speed Strategy: The fastest students recognize flaw patterns from the first sentence or two. Build this pattern recognition through extensive practice with official questions. After 75-100 flaw questions, common patterns become instantly recognizable.
Confidence Builders
- Flaw questions are highly learnable: Pattern recognition improves dramatically with practice
- High accuracy is achievable: 90%+ accuracy is realistic with focused preparation
- Common flaws dominate: Master 8-10 flaw types and you'll recognize most questions
- Frequency makes them crucial: 8-12 flaw questions across both LR sections significantly impact your score
- Wrong answers are predictable: The two-question test eliminates most wrong answers instantly
Key Takeaways
Identify a flaw questions in LSAT Logical Reasoning test your ability to recognize faulty reasoning patterns—a fundamental skill for legal analysis. Attorneys must constantly evaluate arguments, spotting weaknesses before constructing counterarguments or building cases. Success requires understanding the gap between what evidence shows and what conclusions claim, then precisely describing that logical error.
The most common flaws—correlation versus causation and sufficient versus necessary conditions—account for roughly 30-40% of all flaw questions. Master these two patterns first for maximum return on study investment. Other frequent flaws include unrepresentative samples, part-whole confusions, circular reasoning, and false dilemmas. Building a mental catalog of these patterns accelerates recognition and enables quick, accurate responses.
Pattern Recognition + Two-Question Test + Articulation = Consistent Accuracy
The systematic approach works: (1) identify the conclusion, (2) identify the premises, (3) spot the gap or assumption, (4) articulate the flaw in your own words, (5) match your prediction to the answers, (6) apply the two-question test (Did the author do this? Is it a problem?), and (7) eliminate wrong answers. This process, applied consistently, leads to 85-90% accuracy with practice.
Wrong answers follow predictable patterns: describing things the author didn't do, describing things that aren't actually flaws, being too vague, using technical terms incorrectly, or confusing the argument's conclusion with its reasoning. The two-question test exposes these traps instantly. Don't be seduced by sophisticated logical terminology if the answer doesn't describe what this specific argument actually does wrong.
🎯 Your Action Plan
- Master the 8-10 most common flaw types thoroughly
- Obtain official LSAT PrepTests from LSAC.org
- Isolate 50-75 flaw questions for focused practice
- For each question, identify all argument parts and articulate the flaw before checking answers
- Create a flaw journal categorizing each by type
- Focus intensive practice on correlation-causation and sufficient-necessary
- Build answer elimination skills using the two-question test
- Practice explaining why four answers are wrong, not just why one is right
- Track improvement in speed (target: 60-75 seconds per question)
- Aim for 90%+ accuracy through systematic pattern recognition
With mastery of common flaw patterns, systematic application of the two-question test, and disciplined practice articulating reasoning errors precisely, you'll approach flaw questions with confidence, quickly identifying logical gaps and consistently earning these points toward your target LSAT score. Flaw questions reward preparation—invest the time to learn patterns, and you'll reap the scoring benefits.