Rank 1 by frequency | 668 questions in corpus (14.8% of all questions)
A Flaw question presents a stimulus containing an argument with a reasoning error, then asks the test-taker to identify and describe that error. The question does NOT ask you to fix the flaw – it asks you to name what is wrong with the reasoning as it stands. This is the single most common question type on the LSAT Logical Reasoning section. The correct answer is an abstract description of the logical error committed.
Identify the answer choice that most accurately describes the logical error, gap, or vulnerability in the argument's reasoning. The answer describes rather than provides – it characterizes the mistake in abstract, logical terms.
Your ability to recognize common patterns of faulty reasoning and match them to abstract descriptions. This requires (1) identifying the conclusion, (2) seeing why the premises fail to support it, and (3) translating that gap into the abstract language of the answer choices.
1. Background/Context (optional): Sets up the topic or provides factual grounding. Not a premise or conclusion.
2. Premises: Evidence the author offers in support of the conclusion. May include counterarguments, concessions, or subsidiary conclusions. Premises are accepted as true.
The conclusion in a flaw stimulus always outstrips what the premises can logically establish. The evidence does not logically lead to the conclusion. The central error comes down to one of three things: - The reliability of the evidence itself is insufficient - The terms of the conclusion exceed what the evidence establishes - A hidden assumption bridging premises to conclusion is unjustified
Correct answer: - Describes the reasoning error in abstract, logical terms - Satisfies two tests simultaneously: (a) Does the argument actually do this? (b) Is this actually a problem? - Uses abstract variables the test-taker must map onto the specific argument - Uses characteristic language: "takes for granted that," "overlooks the possibility that," "confuses X with Y," "treats a necessary condition as sufficient"
Incorrect answers fail one or both filters: 1. They describe something the argument does NOT actually do 2. They describe something that is NOT actually a problem for this particular argument
Assumes two correlated things have a causal relationship. Sub-patterns: (a) confusing correlation with causation, (b) post hoc reasoning (temporal sequence = causation), (c) ignoring reverse causation, (d) ignoring common third cause, (e) coincidental correlation. 99.9% of the time when the LSAT concludes A causes B from correlation evidence, this flaw is present.
Misapplies conditional statements. Sub-patterns: (a) Mistaken Reversal (affirming the consequent: A->B, B, therefore A), (b) Mistaken Negation (denying the antecedent: A->B, not A, therefore not B). These are logical equivalents of each other.
The conclusion is supported by a premise that is essentially the same as the conclusion. The "proof" merely reiterates what needs to be proven in different words. Can be very hard when disguised with different vocabulary.
Rejects a claim by attacking the proponent rather than addressing the claim itself. Sub-patterns: (a) attacking character, (b) attacking past acts (tu quoque), (c) attacking motivation/bias, (d) attacking the origin. An argument's logical merit is independent of who makes it.
A term with multiple meanings is used inconsistently throughout the argument. Example: "happiness" meaning both "philosophical self-actualization" and "casual pleasure." Difficulty: High – the semantic shift is often extremely subtle.
The correct answer is abstract and descriptive (unlike a Weaken answer, which is concrete and factual). It must satisfy two simultaneous tests: (a) Does the argument actually do this? (b) Is this actually a problem?
"Takes for granted that..." / "Presumes, without providing justification, that..." Something improperly INCLUDED – present in the argument but unjustified.
"Overlooks the possibility that..." / "Fails to consider that..." Something improperly EXCLUDED – absent but should be there. KEY: "Takes for granted" and "overlooks the possibility" are virtual opposites.
1. Describes something the argument does not do: Most common trap. Sounds like a real flaw, but the argument doesn't commit this error. 2. Describes something that is not actually a flaw: Accurately describes part of the argument, but the described feature is not a reasoning error. 3. Right flaw, wrong scope: Similar to the actual flaw but too narrow or too broad. 4. Right concept, wrong wording: Has the same general idea but reverses which element is treated as which. 5. Partially accurate: Describes part of the argument accurately but fails to capture the actual error. 6. Irrelevant flaw: A genuine flaw type that is simply irrelevant to this particular argument.
When the abstract terms in the answer choice are "filled in" with the concrete terms from the stimulus, the description must accurately map onto what the argument does and why it is problematic.
1. Causal/correlation confusion 2. Conditional reasoning errors (necessary/sufficient) 3. Sampling/representativeness errors 4. Numbers/percentages confusion 5. Equivocation 6. Composition/division 7. Appeal to ignorance 8. Ad hominem/source attacks 9. False dichotomy 10. Scope/strength overreach
1. Abstract answer choice language: The most common difficulty multiplier 2. Subtle shifts: Nearly invisible shifts in logic, strength, scope between premises and conclusion 3. Multiple apparent flaws: Several errors seem present; diligent analysis needed 4. Unstated assumptions as the flaw: The flaw is a hidden assumption 5. Confusing language in stimulus: Dense, complex arguments where identifying the conclusion requires careful reading 6. "Plan B" Strategy (PowerScore): When unable to identify the abstract flaw, consider how you would WEAKEN the argument. If you can understand how to weaken it, you fundamentally grasp the flaw. Then find the answer choice describing that weakness as a logical error.
1. Read the stimulus and identify the conclusion (look for "therefore," "thus," "hence," "consequently," "so") 2. Identify the premises (noting background, counterarguments, concessions) 3. Ask: "Why don't these premises prove this conclusion?" – do not subconsciously help the argument 4. Prephrase the flaw before looking at answer choices 5. Match your prephrase using the "Mad Libs" technique 6. Test each answer with two filters: (a) Does the argument actually do this? (b) Is this actually a problem? 7. If stuck, use Plan B: think about how to weaken, then find the answer describing that weakness
Source: PT20, Section 4, Question 14
Stimulus: "A leading economist has determined that among people who used computers at their place of employment last year, those who also owned portable ('laptop') computers earned 25 percent more on average than those who did not. It is obvious from this that owning a laptop computer led to a higher-paying job."
Source: PT22, Section 4, Question 21
Stimulus: Two speakers (Terry and Pat) both commit the same error about "favorable consequences" and goodness. Terry argues: some bad-by-society actions have favorable consequences; good actions require favorable consequences; therefore some bad-by-society actions are good. Pat makes a parallel error.
Source: PT51, Section 1, Question 6
Stimulus: Deirdre argues that philosophers who say happiness (deep fulfillment from living up to one's potential) is elusive have "exaggerated the difficulty of being happy" because simply walking along the seashore on a sunny afternoon causes feelings of happiness.
Source: PT14, Section 4, Question 15
Stimulus: A magazine article dismisses the Environmental Commissioner's proposals because they resemble proposals from Tsarque Inc., a known polluter whose chief is a friend of the commissioner.