LSAT Logical Reasoning Flaw Questions: Free Practice Quiz
Flaw questions are one of the highest-frequency question types in the LSAT's Logical Reasoning section. You're handed a short, defective argument and must pick, from five answer choices (A–E), the one that most accurately describes what's wrong with the reasoning. These 12 original LSAT-style drills cover the flaw types the test loves most — necessary vs. sufficient, correlation vs. causation, unrepresentative samples, circular reasoning — each with a full explanation.
0 / 12 answered
Q1
A recent study found that people who drink coffee regularly tend to live longer than those who don't. The researchers concluded that drinking coffee regularly extends a person's life.
Q2
To be admitted to the honors program, a student must maintain a GPA of at least 3.5. Maria has a GPA of 3.8. Therefore, Maria will be admitted to the honors program.
Q3
A radio host asked listeners to call in and say whether they support raising the local sales tax. Of the 200 people who called, 85% opposed the increase. The host concluded that a large majority of the city's residents oppose raising the sales tax.
Q4
This film deserves the award for best picture, because it is the best film of the year. And it clearly is the best film of the year, since no other film this year is as deserving of the best-picture award.
Q5
Dr. Lang argues that the new bridge is structurally unsafe and should be closed. But Dr. Lang was once fined for a parking violation, and she is known to dislike the mayor who approved the bridge. So there is no reason to accept her claim that the bridge is unsafe.
Q6
Councilmember Ruiz proposes that the city spend more on repairing existing roads before it builds any new ones. But we should reject her plan to halt all new construction indefinitely: a growing city cannot simply freeze its development and still expect to thrive.
Q7
A free press is essential to democracy. But anything that is free should not cost anyone money. Therefore, to protect democracy, newspapers must be provided to readers at no charge.
Q8
No researcher has ever proven that the supplement has any harmful side effects. Therefore, we can be confident that the supplement is completely safe to take.
Q9
Every player on the national team is an outstanding athlete. Therefore, the national team is sure to be an outstanding team, and it will win the tournament.
Q10
Either we cut the city's arts budget entirely, or we will be forced to raise everyone's taxes. Since no one wants higher taxes, we have no choice but to eliminate arts funding altogether.
Q11
This year the Northside clinic had a higher percentage of successful surgeries than the much larger Central Hospital did. So Northside must have successfully completed more surgeries than Central Hospital did this year.
Q12
The new investing app is the most downloaded finance app in the country, and its user base is growing faster than any competitor's. So it must be the best app available for managing your money.
Answer all 12 questions to see your result 👆
The high-frequency LSAT flaw types, decoded
- Necessary vs. Sufficient
- Asked as 'confuses a condition sufficient for X with one required for X.' Spot it when the argument shows a requirement was met, then declares the outcome guaranteed.
- Correlation ≠ Causation
- Asked as 'treats a correlation as evidence of a causal relationship.' Spot it when two things merely occur together and the author says one caused the other.
- Unrepresentative Sample
- Asked as 'draws a conclusion about a population from an unrepresentative sample.' Spot self-selected callers, volunteers, or a group too small or too special to generalize from.
- Circular Reasoning
- Asked as 'presupposes the very thing it sets out to prove.' Spot a premise that is just the conclusion reworded.
- Ad Hominem
- Asked as 'rejects a claim by attacking the person who advanced it.' Spot an attack on character, motive, or hypocrisy instead of on the argument.
- Straw Man
- Asked as 'misrepresents the opponent's position.' Spot a proposal restated in a more extreme, easier-to-refute form.
- Equivocation
- Asked as 'relies on a shift in the meaning of a term.' Spot a key word that means one thing in a premise and another in the conclusion.
- Appeal to Ignorance
- Asked as 'takes the absence of evidence for a claim as evidence against it.' Spot 'no one has proven X, therefore not-X.'
How to spot flaws on LSAT Logical Reasoning
On the LSAT, Logical Reasoning is built around short arguments, and flaw questions — which ask you to identify the reasoning error in an argument — are one of the most common tasks you'll face. The stem usually reads 'Which one of the following most accurately describes a flaw in the argument's reasoning?' or 'The reasoning in the argument is flawed because it...' Because the same handful of error patterns recur again and again, flaw questions are among the most learnable points on the whole test: once you can name the flaw, the right answer often jumps out.
The single most-tested pattern is confusing necessary and sufficient conditions. A necessary condition must be met for something to happen; a sufficient condition, on its own, guarantees it. When an argument establishes that a requirement was met and then leaps to 'so the outcome is guaranteed,' it has treated a necessary condition as if it were sufficient. Training your ear for 'must,' 'only if,' 'requires,' and 'guarantees' pays off on more LSAT questions than almost anything else you can practice.
The next family to master is causal reasoning. Correlation-vs-causation flaws — where two things merely occur together and the author concludes one caused the other — appear constantly, along with their cousins: overlooking an alternative cause, ignoring the possibility that the causation runs the other way, and treating 'happened after' as 'happened because of.' Whenever a conclusion asserts that X causes Y, ask what else could explain the link.
The reliable way to spot flaws is to pre-phrase. Read the argument, find the conclusion, find the evidence, and — before you look at the answer choices — say in your own words what's wrong with the jump from evidence to conclusion. Then find the choice that matches your pre-phrase. The order matters: LSAT flaw answers are deliberately written so several 'look right,' and the trap choices describe real flaws that simply aren't present in this argument. Naming the flaw first inoculates you against them.
Flaw questions aren't an island. The same skill powers Assumption, Weaken, and Necessary Assumption questions — all of them turn on seeing the gap between an argument's evidence and its conclusion. Get fluent at flaws and you're simultaneously training the most transferable skill in the entire Logical Reasoning section.
Here's the part most prep courses skip: every LSAT flaw is just a logical fallacy or cognitive bias with a formal name. Ad hominem, straw man, false dilemma, appeal to popularity, circular reasoning — these are the same traps that derail arguments online, in the news, and inside your own head. That's why the fastest way to build LSAT flaw intuition is to get comfortable with the underlying fallacies and biases first, then drill the LSAT-specific format. Do a few timed sets, review every miss by naming the flaw type, and keep a running list of the trap answers that fooled you.
LSAT flaw questions FAQ
What are flaw questions on the LSAT?
Flaw questions are a Logical Reasoning question type that hands you a short argument containing a reasoning error and asks you to identify what that error is. The stem typically reads 'Which one of the following most accurately describes a flaw in the argument's reasoning?' Each question has five answer choices (A–E); the correct one names the specific mistake the argument actually makes, while the wrong choices describe flaws that aren't present. It's one of the most frequent question types in the LR section.
What is the most common LSAT flaw type?
There's no single official ranking, but a few families dominate: confusing necessary and sufficient conditions (conditional-logic errors) and causal flaws (treating a correlation as causation, overlooking alternative causes) are consistently among the most frequently tested. Unrepresentative samples and circular reasoning are close behind. Master those and you've covered a large share of the flaw questions you'll see.
Are these real LSAT questions?
No. Every question here is original, LSAT-style practice written to mirror the format, difficulty, and flaw types of real Logical Reasoning questions — but none is taken from an actual LSAT. Real LSAT questions are copyrighted by LSAC, so reputable prep materials (this quiz included) use original practice items. Use official LSAC PrepTests when you want to drill on released real questions.
How many flaw questions are on the LSAT?
It varies from test to test. Flaw questions are one of the highest-frequency question types within each Logical Reasoning section, but LSAC doesn't publish a fixed count, and the exact mix of question types shifts between exams. Rather than memorizing a number, treat flaw questions as a core, always-present part of LR that is well worth the study time.
How do I get better at LSAT flaw questions?
Learn the recurring flaw types by name, then pre-phrase: before reading the answer choices, state in your own words what's wrong with the argument, and match that to an answer. Review every miss by identifying which flaw it was and why the trap choice fooled you. Because these flaws are really everyday logical fallacies and cognitive biases, building that underlying intuition first — for example in our free Brain Traps course — makes the LSAT-specific drilling go much faster.