LSAT Quiz: Describe The Flaw
20 questions · exam conditions
0:00
Describe The FlawQuestion 1 of 20

Each of our four departments reported higher productivity this quarter than last when measured as tasks completed per employee hour. Marketing rose from 4 to 5, Sales from 6 to 7, Engineering from 3 to 4, and Support from 5 to 6. Therefore, the company as a whole must have increased its productivity. We should promise investors that overall output per hour improved accordingly.

The reasoning above is flawed for which of the following reasons?

It mistakes the mere absence of any reported counterexample for positive proof that a sweeping general claim about the company must be true.
It assumes that whatever practice turns out to be the most efficient in a given quarter must also be the ethically acceptable one to pursue.
It infers a confident prediction about future companywide performance from a single isolated instance of past improvement in one department.
It takes the existence of a correlation between two measured factors to establish that the first of those factors actually causes the second.
It assumes that what is true of each part must be true of the whole, ignoring differences in size or weighting among the parts.
← Back to quizzes

LSAT Quiz

LSAT Quiz: Describe The Flaw

Practice Describe The Flaw in LSAT with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Describe The Flaw, giving you a quick way to practice the rules, question types, and explanations that matter most for LSAT.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

Each of our four departments reported higher productivity this quarter than last when measured as tasks completed per employee hour. Marketing rose from 4 to 5, Sales from 6 to 7, Engineering from 3 to 4, and Support from 5 to 6. Therefore, the company as a whole must have increased its productivity. We should promise investors that overall output per hour improved accordingly.

The reasoning above is flawed for which of the following reasons?

  1. It mistakes the mere absence of any reported counterexample for positive proof that a sweeping general claim about the company must be true.
  2. It assumes that whatever practice turns out to be the most efficient in a given quarter must also be the ethically acceptable one to pursue.
  3. It infers a confident prediction about future companywide performance from a single isolated instance of past improvement in one department.
  4. It takes the existence of a correlation between two measured factors to establish that the first of those factors actually causes the second.
  5. It assumes that what is true of each part must be true of the whole, ignoring differences in size or weighting among the parts. (correct answer)

Explanation: The argument concludes that the whole company's productivity rose just because each department's per-hour rate rose. That is a composition error: a company-wide average is weighted by how many hours each department contributes, so if hours shift toward departments with lower rates, the overall average can fall even when every department improves. The correct choice names exactly this — treating what is true of each part as automatically true of the whole while ignoring size and weighting. The counterexample choice is wrong because the argument never reasons from a lack of counterexamples; it reasons from positive data. The efficiency-to-ethics choice imports a moral standard the argument never raises. The future-prediction choice misdescribes the reasoning, which draws a present conclusion from four departments, not a forecast from one isolated case. The correlation-to-causation choice is wrong because no causal claim is made — the conclusion is about an aggregate total, not about one factor producing another.

Question 2

The research team reports a significant difference in test performance between students who drank coffee and those who abstained in a controlled study. Given that the difference is significant, switching the campus cafeteria to serve only coffee will produce large improvements in grades across departments. Since significance indicates a big effect, the policy is justified and should be implemented immediately.

The reasoning above is flawed for which of the following reasons?

  1. It confuses a condition that is merely necessary for improved grades with one that is by itself sufficient to guarantee them.
  2. It rests its cafeteria recommendation on a premise about coffee that the argument itself has elsewhere explicitly rejected as false.
  3. It concludes that the coffee policy is entirely ineffective merely because that policy is not perfectly effective in every department.
  4. It equivocates between statistical significance and practical magnitude, treating any statistically significant finding as evidence of a large effect. (correct answer)
  5. It relies on a single anecdote about one student rather than controlled empirical evidence to justify a broad campus-wide policy.

Explanation: The argument slides from 'the difference is statistically significant' to 'the effect is large enough to justify a campus-wide policy.' But statistical significance only indicates that a difference is unlikely due to chance; it says nothing about the size or practical importance of the effect. Treating significance as proof of a big effect is the equivocation, so that choice is correct. The necessary/sufficient option misdescribes the argument: it never sorts conditions into necessary versus sufficient roles. The self-contradiction option is wrong because the argument never rejects the coffee premise it relies on—it endorses it throughout. The 'not perfectly effective' option is wrong because the argument overstates the policy's benefit rather than dismissing it for imperfection. The anecdote option is wrong because the evidence cited is a controlled study, not a single student's story.

Question 3

According to a recent civic profile, most members of the city council are licensed attorneys, which explains the council's focus on legalistic policy drafting. Therefore, most of the city's licensed attorneys must be serving on the city council. Given the council's makeup, it is reasonable to conclude that a typical lawyer in this city participates directly in municipal governance.

The argument's reasoning is most vulnerable to criticism on the grounds that it

  1. overlooks the possibility that the council's legalistic focus may stem from several contributing causes rather than a single one
  2. treats the mere absence of evidence contradicting its claim as sufficient to establish that claim conclusively
  3. generalizes about the habits of an entire professional category by relying on a handful of unrepresentative individual cases
  4. illicitly converts a statement about most members of one group into a statement about most members of another group (correct answer)
  5. trades on an ambiguity in the term 'lawyer' by employing it in two subtly different senses across the argument

Explanation: The argument starts from 'most council members are lawyers' and slides to 'most lawyers are council members.' That reversal is illegitimate: most of a small group (the council) being lawyers tells you nothing about what most of a large group (the city's lawyers) do. This is the flaw described by the option about illicitly converting a claim about most of one group into a claim about most of another. The option about multiple contributing causes is wrong because the argument's error is not causal—it never disputes why the council drafts legalistic policy. The option about absence of contradicting evidence is wrong because the argument cites positive evidence (the council's makeup), not a lack of counterevidence. The option about generalizing from a handful of unrepresentative cases is wrong because the argument reasons from a majority claim, not from a few atypical examples. The option about an ambiguity in 'lawyer' is wrong because the term keeps a single, consistent meaning throughout; nothing shifts. Only the conversion of quantified statements captures what actually goes astray.

Question 4

Grant reviewers insist that only thoroughly researched proposals are ever funded; superficial work never gets approved. Our team's project has been carefully researched for two years and cites extensive prior studies. Last cycle, committees rejected every application judged under-researched, which shows that thorough research is a prerequisite for success. On that basis, we can be confident ours will be approved.

Which of the following most accurately describes the error in reasoning?

  1. Attacks the grant committee members rather than their criteria.
  2. Concludes a causal claim merely from the order in which events occur.
  3. Generalizes from a single case to an entire category.
  4. Presumes that two things similar in one respect are similar in all respects.
  5. Treats a necessary condition for success as if it were sufficient to guarantee success. (correct answer)

Explanation: The argument assumes that because thorough research is required for funding, having thorough research ensures funding. It does not depend on an analogy, a personal attack, or a hasty generalization. Nor does it infer causation from sequence.

Question 5

Last year, car thefts increased by 50 percent in Lakeview but only by 10 percent in Harbor City. Therefore, car theft is now a more serious problem in Lakeview than in Harbor City, and the regional task force should devote most of its resources to Lakeview. Since Lakeview's increase was higher, more cars must have been stolen there, and the trend shows that Lakeview is where intervention will have the greatest impact.

The reasoning above is flawed for which of the following reasons?

  1. It bases its conclusion on a sample that is unlikely to be representative of the group about which it draws a conclusion.
  2. It confuses a comparison of percentages with a comparison of absolute numbers, ignoring differences in base rates. (correct answer)
  3. It treats two alternatives as mutually exclusive when both could be true.
  4. It draws a universal generalization from a single, atypical instance.
  5. It rejects a claim solely on the basis of its source.

Explanation: A higher percentage increase does not show which city has more thefts without knowing the initial totals. The argument does not hinge on sampling, false dichotomy, or source-based dismissal. It also does not generalize from a single case.

Question 6

An electronics blogger surveyed readers who commented on her website and found that 92 percent prefer brand X headphones to brand Y. Because the commenters are headphone enthusiasts who pay close attention to audio quality, this result shows that the broader population of music listeners overwhelmingly prefers brand X. Thus, retailers should stock far more of brand X to meet public demand.

The reasoning above is flawed for which of the following reasons?

  1. It generalizes from an unrepresentative sample to a broad population. (correct answer)
  2. It presumes that because two brands are different, one must be superior.
  3. It concludes that a policy is effective merely because it is popular.
  4. It equates a lack of contrary evidence with conclusive proof.
  5. It overlooks the possibility that preferences can change over time, invalidating the result.

Explanation: Website commenters are a self-selected group that is unlikely to represent the broader population. Generalizing their preferences to all listeners is an unrepresentative sample flaw. The other options describe different errors (false dichotomy, appeal to popularity, appeal to ignorance, and temporal change) not made here.

Question 7

Facing a budget shortfall, the museum must either raise ticket prices or run a deficit. Raising prices would alienate visitors, so the board should accept a deficit. Hence, there is no feasible way to avoid a deficit without increasing prices; grants and donations are unreliable and thus cannot help. Cutting costs is unrealistic because the museum has already reduced staff once.

The reasoning above is flawed for which of the following reasons?

  1. It presumes that a practice that is common is therefore acceptable.
  2. It concludes that because something is possible, it is inevitable.
  3. It infers causation from mere temporal sequence.
  4. It presents a false dilemma by overlooking other plausible means of balancing the budget. (correct answer)
  5. It generalizes from a single department to the entire institution without basis.

Explanation: The argument treats raising prices or running a deficit as exhaustive while inadequately considering other options for balancing the budget. The other answer choices describe flaws not committed here.

Question 8

Last quarter, Store A increased its customer base by 20 percent, while its rival, Store B, increased its base by only 10 percent. The marketing director concludes that Store A added more customers than Store B and thus had the more successful campaign. Since percentage growth measures improvement fairly across companies, no further information is needed to compare their gains. Therefore, the director allocates next year's budget primarily to Store A's strategy.

The reasoning above is flawed for which of the following reasons?

  1. It treats a percentage increase as if it established a greater absolute increase in number. (correct answer)
  2. It assumes that because one event follows another, the first caused the second.
  3. It disputes a position by attacking the rival's motives rather than the evidence.
  4. It restates its conclusion as a premise instead of providing support for it.
  5. It shifts the meaning of a key term during the course of the argument.

Explanation: A larger percentage increase does not guarantee a larger number of customers added if the initial bases differ. The argument does not infer causation from sequence, attack motives, or argue in a circle. There is no equivocation on a key term.

Question 9

In our orchestra, every section improved its timing this season according to section rehearsals. The strings now hit their cues, the brass stays within tempo, and the percussion no longer rushes entrances. Therefore, our full-orchestra performances must now be perfectly synchronized. The conductor has not changed, and the repertoire is the same, so these improvements show that the concerts will be flawless.

The reasoning above is flawed for which of the following reasons?

  1. It fails to consider that a change in leadership could undermine performance.
  2. It uses an unrepresentative sample to generalize about the entire orchestra.
  3. It draws a causal conclusion without ruling out alternative causes.
  4. It infers that the whole will have a property merely because each part has that property in isolation. (correct answer)
  5. It assumes that because the repertoire is the same, audience reactions will not change.

Explanation: The argument assumes that improvements in individual sections guarantee perfect synchronization of the entire ensemble, ignoring interactions among sections. Properties of parts do not necessarily transfer to the whole. The other choices introduce issues (sampling, causation, leadership, audience reactions) not central to the reasoning.

Question 10

To determine the town's coffee preferences, a local cafe polled 20 of its most frequent patrons and found that 18 prefer dark roast. From this, we can conclude that residents across the town overwhelmingly prefer dark roast. Because these regulars are enthusiastic coffee drinkers, their opinions are especially informed and thus representative of everyone in town. Therefore, the city should stock more dark roast at public events.

The reasoning above is flawed for which of the following reasons?

  1. It bases a general conclusion about a population on an unrepresentative sample. (correct answer)
  2. It presumes that a necessary condition is sufficient for the outcome in question.
  3. It infers that what is true of a part must be true of the whole.
  4. It attacks the motives of those who hold a contrary view rather than addressing their arguments.
  5. It equivocates on the meaning of the term 'preference.'

Explanation: Frequent patrons of one cafe are unlikely to represent the town as a whole. The other options describe different flaws—conditional confusion, composition, ad hominem, and equivocation—that are not committed here.

Question 11

Industry analyses show that most companies that achieve rapid growth have founders with prior startup experience and a focus on product design. Our company has both of those traits. Therefore, it is likely to achieve rapid growth. Moreover, investors often praise teams like ours, which further confirms that conclusion. Although market conditions vary, the presence of these traits is what sets winners apart.

The reasoning above is flawed for which of the following reasons?

  1. It assumes that if a condition is sufficient for an outcome, then it is also necessary for that outcome.
  2. It treats characteristics that are common among successful firms as if they were by themselves sufficient to ensure success. (correct answer)
  3. It draws an analogy to investors' opinions without showing they are representative.
  4. It infers a trend from a single, atypical case.
  5. It discounts negative evidence solely because it is inconvenient.

Explanation: The argument moves from 'most successful firms have traits T' to 'having T makes success likely,' illegitimately treating a typical feature of successes as sufficient. Many firms with T may still fail. The distractors describe other flaws (necessity/sufficiency reversal, weak analogy, hasty generalization, evidence dismissal) not shown here.

Question 12

An online news site surveyed its subscribers and found that 68 percent preferred candidate Rivera over candidate Holt. Because such a large majority favors Rivera among our readers, it is clear that Rivera will win the citywide election. The site's subscriber base is large and the poll received thousands of responses, so it is a reliable indicator of public sentiment.

Which one of the following most accurately describes a flaw in the argument?

  1. It treats a condition that is necessary for electoral victory as if it were sufficient.
  2. It confuses what is true of parts of the electorate with what is true of the whole.
  3. It infers a causal explanation merely from a sequence of events.
  4. It bases a prediction on a sample that is not representative of the electorate. (correct answer)
  5. It concludes that a practice will persist simply because it has occurred in the past.

Explanation: The poll reflects the preferences of an online subscriber base, which is not representative of the citywide electorate. Concluding a citywide outcome from that biased sample is flawed. The other options describe errors (necessary/sufficient, part-whole, post hoc, inertia) the argument does not make.

Question 13

To cut downtown congestion, the transportation director argues, the city has only two viable options: raise parking fees or ban cars from the center. Because raising fees would unfairly burden low-income workers, the city must ban cars. That will be the most equitable way to reduce traffic. Public transit upgrades, she says, are too slow to matter. Therefore, no other approach could achieve the goal.

The argument's reasoning is most vulnerable to criticism on the grounds that it

  1. Concludes that one policy caused an effect because they occurred together.
  2. Treats two options as the only possibilities when others are available. (correct answer)
  3. Generalizes from an exceptional case.
  4. Confuses a necessary condition with a sufficient condition.
  5. Assumes that what is true now must have been true in the past.

Explanation: The director falsely limits the choices to two, ignoring other plausible strategies for reducing congestion. The reasoning does not hinge on a causal correlation, a sampling issue, or a temporal assumption. Nor does it mistake necessary for sufficient conditions.

Question 14

At the annual gourmet food expo, we surveyed 500 attendees and found that 72 percent prefer artisanal soda to water with meals. Therefore, most people in our city prefer artisanal soda to water, so the municipal vending contract should stock more soda than water in public buildings. After all, the expo draws enthusiastic food lovers, which makes them particularly attuned to what the broader public wants.

The reasoning above is flawed for which of the following reasons?

  1. It bases a conclusion about a population on a sample that is unlikely to be representative of that population. (correct answer)
  2. It treats a correlation as though it established a necessary condition.
  3. It confuses the meaning of a key term in the course of the argument.
  4. It claims that because something has not been shown to be false, it is true.
  5. It concludes that what is true of a whole must be true of each part.

Explanation: Expo attendees are self-selected food enthusiasts and likely not representative of the city's overall population. The argument does not hinge on necessary conditions, semantic shifts, or absence-of-evidence reasoning. It also does not move from whole-to-part.

Question 15

City health inspectors have not found any documented cases of illness linked to meals from Street Eats, a popular new food truck, during its first month of operation. Therefore, the truck's food preparation is safe, and concerns about sanitation are unfounded. Since no reports have surfaced, it is clear there is nothing to worry about. Indeed, satisfied customers have posted numerous positive reviews, which would surely be impossible if illnesses were occurring.

The reasoning above is flawed for which of the following reasons?

  1. It bases its conclusion on the fact that many people approve of the practice.
  2. It mistakes an effect for a cause.
  3. It infers that there is no problem merely from the absence of evidence of a problem. (correct answer)
  4. It presumes that a necessary condition is also sufficient.
  5. It draws a general conclusion from an unrepresentative anecdote.

Explanation: The argument takes the lack of reported illnesses as proof that the food is safe, treating absence of evidence as evidence of absence. It does not reverse cause and effect or confuse necessary and sufficient conditions. While it mentions popularity, that is not its logical basis, and it does not rely on a single anecdote.

Question 16

After the city replaced its streetlights with LEDs, traffic accidents fell by 10 percent within six months. Clearly, the LED lights caused drivers to be safer. The police chief's stepped-up enforcement began during the same period but was widely criticized and thus likely had no effect, so the lighting change must be the reason accidents declined. Therefore, further investment in lighting will continue to reduce accidents.

The reasoning above is flawed for which of the following reasons?

  1. It concludes that a policy is unethical solely because it is unpopular.
  2. It draws a sweeping generalization from a single counterexample.
  3. It treats a mere correlation as if it established a causal relationship. (correct answer)
  4. It bases a conclusion on responses from a self-selected group.
  5. It relies on an ambiguous term whose meaning shifts within the argument.

Explanation: A temporal association is taken to show causation while alternative explanations are dismissed without support. The other choices describe flaws (ethical leap, hasty generalization, sampling bias, equivocation) not present.

Question 17

Philosophers often argue that no rational person believes in miracles, meaning events that violate natural laws. After last night's game, Hannah said her team's comeback was a miracle and credited it with changing the season's momentum. From this, it follows, the coach claims, that Hannah is not rational, since she openly believes in miracles. He added that only a credulous fan would talk that way.

The reasoning above is flawed for which of the following reasons?

  1. Illicitly shifts the meaning of a critical term in the course of the argument. (correct answer)
  2. Infers a general principle from a few atypical cases.
  3. Presupposes what it sets out to establish.
  4. Presents two options as exhaustive when other possibilities exist.
  5. Fails to consider that a correlation may be due to a third factor.

Explanation: The argument equivocates on 'miracle,' using a technical sense to condemn a figurative usage. It does not beg the question or restrict options. Nor does it generalize from atypical cases or infer causation from correlation.

Question 18

Anyone capable of producing accurate, lifelike portrait drawings has studied human anatomy, since such knowledge is essential for realism. Gabe has completed an anatomy course. Therefore, Gabe is capable of producing accurate, lifelike portrait drawings. Because the prerequisite is present in Gabe's case, the result must follow. His instructor even emphasized that no student could excel at realism without that foundation, so anatomy plainly matters.

The reasoning above is flawed for which of the following reasons?

  1. It presumes that an ability common among experts cannot also be found among novices.
  2. It concludes that a skill cannot be learned outside formal instruction.
  3. It fails to consider that the concept of realism may be culturally relative.
  4. It generalizes from an instructor's opinion to a universal scientific law.
  5. It treats a necessary condition for achieving a result as though it were sufficient to guarantee that result. (correct answer)

Explanation: The argument mistakes a necessary condition (studying anatomy) for a sufficient one and thus affirms the consequent. The other choices raise issues of expertise, cultural relativity, authority, or formal instruction not relied upon.

Question 19

Clinic data show that patients taking the new blood-pressure drug reported fewer side effects than those on the current standard therapy. Hence the new drug carries less risk and, overall, is safer for the public; we should replace the standard therapy with it. While long-term mortality outcomes are not yet measured, the reduction in side effects clearly shows the risk profile is better.

The reasoning above is flawed for which of the following reasons?

  1. It concludes that a short‑term correlation will persist indefinitely into the future.
  2. It dismisses expert evidence solely because the experts may be biased.
  3. It equivocates by using the term 'risk' to refer to side-effect frequency in the premise and overall safety in the conclusion. (correct answer)
  4. It assumes that what is true of a sample of patients must be true of all patients.
  5. It confuses a higher percentage of positive outcomes with a higher absolute number of positive outcomes.

Explanation: The argument slides from fewer side effects (one dimension of risk) to greater overall safety, shifting the meaning of 'risk.' That ignores other outcomes like efficacy and mortality. The other options (e.g., bias attack, percentage/amount, overgeneralization) do not capture the specific ambiguity here.

Question 20

Whenever a houseplant receives at least six hours of sunlight, it grows vigorously. My fern grew vigorously this month, so it must have received at least six hours of sunlight. Thus, vigorous growth can be ensured simply by providing six hours of sunlight, and other factors like soil nutrients are beside the point. However, the fern sits far from any window, making sunlight an unlikely cause.

The reasoning above is flawed for which of the following reasons?

  1. It concludes that because one event followed another, the first caused the second.
  2. It treats a condition sufficient for an outcome as though it were necessary for that outcome. (correct answer)
  3. It draws a conclusion about the whole based solely on characteristics of a part.
  4. It relies on a sample that is too small to support the generalization it draws.
  5. It equivocates on the meaning of the term 'sunlight.'

Explanation: From vigorous growth the argument infers six hours of sunlight, thereby treating a sufficient condition as necessary (affirming the consequent). The other options describe different flaws not present.