From first principles to mastery. Covers every flaw type the LSAT tests, the exact language patterns used in correct answers, five fully worked questions with interactive answer reveal, and a complete practice drill set.
Before we get into tactics, let us agree on what we are actually dealing with. A Flaw question gives you an argument — a set of premises leading to a conclusion — and asks you to identify what is logically wrong with it. The argument always has a problem. Your job is to name that problem precisely, in the same terms the correct answer uses.
You will recognise a Flaw question by its stem. The most common phrasings you will see are:
The reasoning in the argument is flawed because the argument...
The argument's reasoning is most vulnerable to criticism on the grounds that...
Which one of the following identifies a flaw in the argument's reasoning?
The argument above is most vulnerable to which of the following objections?
When you see any of these, the approach is identical every time. Find the gap in the argument, understand why it is a problem, and match it to the answer choice that describes it most accurately.
Flaw questions appear frequently — typically four to six times on a single LSAT. They are among the most learnable question types because every flaw the LSAT tests has appeared before. There is a finite list. Once you know that list, you stop discovering flaws and start recognising them. That shift, from discovery to recognition, is what separates a 155 from a 170 on this question type.
Every LSAT argument has the same structure. There are premises — statements offered as evidence — and there is a conclusion — the claim the argument is trying to establish. In a valid argument, the conclusion follows necessarily from the premises. In a flawed argument, it does not. There is a gap: something unstated and unjustified that the argument silently assumes must be true in order for the conclusion to hold.
Here is a simple example. Consider this argument:
Premise: Every time I eat at this restaurant, the food takes forty minutes to arrive.
Conclusion: The chef at this restaurant is slow.
The premise is about food taking a long time. The conclusion is about the chef being slow. But there is a hidden leap: the argument assumes the delay is caused by the chef, when it could equally be caused by an understaffed wait team, a large volume of orders, or a dozen other things. That hidden, unjustified assumption is the flaw.
Your task on every Flaw question is to find that gap and describe it. The correct answer will name the logical error precisely. The four wrong answers will either describe flaws that are not present in the argument, or describe something the argument did accurately but in a way that sounds like a criticism when it is not actually a logical error.
Before you look at the answer choices, you should be able to answer this question in your own words: why does the conclusion not follow from the premises? If you can articulate the problem clearly before reading the choices, you will find the right answer far more quickly and accurately.
Two productive questions to ask yourself as you read every stimulus:
1. What does the conclusion actually claim?
Be precise. A conclusion that says "this policy will reduce crime" is very different from one that says "this policy might reduce crime." The exact words matter enormously on the LSAT.
2. What would need to be true for the premises to actually support that conclusion?
Whatever must be assumed but is not stated — that is the flaw. The argument is treating an assumption as though it were a proven fact.
The LSAT draws on a specific, recurring set of logical errors. Every Flaw question you will ever see falls into one of the categories below. Click each card to read the full definition, a plain-language example, and the exact language the LSAT uses in correct answers.
This is the single most tested flaw on the LSAT. The argument observes that two things occur together — that they are correlated — and concludes that one must be causing the other. But correlation alone does not establish causation. Both things could be caused by a third factor, the causal direction could be reversed, or the co-occurrence could be coincidental.
A close relative of the causation flaw. Here the argument does establish that X caused Y, but then draws a further conclusion that ignores the possibility that something else could have produced the same result. The argument treats one identified cause as though it must be the only possible cause.
The argument draws a broad conclusion about a large group based on evidence about a small or unrepresentative sample. The sample may be too small, too specific, or selected in a way that makes it unrepresentative of the population the conclusion is about.
The argument moves between relative figures and absolute figures as though they mean the same thing. A higher percentage does not mean a larger absolute number if the total populations differ significantly. Conversely, a larger absolute number does not mean a higher rate.
A sufficient condition guarantees a result. A necessary condition is required for a result but does not alone guarantee it. The argument treats one as the other. The two most common errors: assuming that because a sufficient condition is absent, the result cannot occur (denying the antecedent); and assuming that because a necessary condition is present, the result must occur (affirming the consequent).
The conclusion of the argument is simply a restatement of one of the premises. The argument uses what it is trying to prove as evidence for that very conclusion — it goes in a circle rather than making a genuine logical step forward.
The argument presents two options as though they are the only possibilities, eliminates one, and concludes the other must be true. In reality, there are other options the argument ignores entirely. The either/or framing is not justified by the evidence.
The argument uses the same word or phrase in two different senses, treating them as though they mean the same thing when they do not. The logical step depends entirely on this hidden shift in meaning — if you held the word to one definition throughout, the argument would collapse.
Composition: what is true of each individual part must be true of the whole. Division: what is true of the whole must be true of each individual part. Both are invalid inferences. A team of excellent players may play poorly together. An excellent team may contain weaker individual players.
The premises establish a claim about one thing, but the conclusion makes a claim about something slightly but importantly different. The subject, scale, or nature of the claim shifts between the evidence and the conclusion in a way the argument never justifies. This is one of the subtlest flaws on the LSAT — the shift is often just a single word.
The premises show that something could be, might be, or is possibly true. The conclusion then states it as though it definitely is true. The argument upgrades the strength of the claim without any additional justification — crossing from possible to certain in a single, unjustified step.
The argument compares two things and concludes that because they are similar in one respect, they must be similar in another. The comparison is flawed because the two things differ in ways that are relevant to the conclusion being drawn.
The evidence is drawn from one point in time, but the conclusion is about a different time period. The argument assumes conditions have stayed constant when they may have changed significantly.
The argument attacks the character, credibility, or motives of a person rather than addressing the substance of their argument. Even if the criticism of the person is accurate, it tells us nothing about whether their argument is logically sound.
The argument cites an expert or authority as support for a claim, but the authority's expertise is in a different field, or the authority is not genuinely an expert in the relevant area. Note: an appeal to authority is only a flaw when the authority is inappropriate — citing a genuine relevant expert is valid reasoning.
The argument concludes that something is true, correct, or good because many people believe it, do it, or approve of it. The number of people who hold a view has no bearing on whether that view is logically correct.
The argument misrepresents an opposing view — exaggerating it, oversimplifying it, or distorting it — and then refutes the misrepresentation rather than the actual position. A straw man is easier to knock down than the real argument, which is precisely why it is used.
The argument concludes that because no one has proven X is false, X must be true. The absence of evidence against a claim is not evidence for it. Absence of disproof is not equivalent to proof.
A consistent process matters enormously on timed questions. Here is the exact sequence to follow every single time you encounter a Flaw question.
Separate the premises from the conclusion as you read. Ask yourself: what is this argument trying to prove? Signal words like "therefore", "thus", "so", and "hence" typically introduce conclusions. Words like "because", "since", and "given that" typically introduce premises. If there is no signal word, the conclusion is often the first or last sentence.
After reading the stimulus, pause. Ask: why does the conclusion not follow from the premises? Name the flaw in your own words — even one or two words is enough. "Causation from correlation." "False dichotomy." "Ad hominem." Having a pre-formed answer makes you far less susceptible to the traps the wrong choices set.
Read the answer choices looking for the one that matches what you identified. You are not discovering the flaw from the choices — you are confirming it. The correct answer will describe the logical error accurately and in abstract terms. It will not necessarily mention the specific content of the argument.
If more than one choice seems plausible, ask: does this answer describe a flaw that is actually present in this specific argument? An answer may describe a genuine logical flaw but simply not be the flaw committed here. That answer is wrong. The correct answer must describe what went wrong in this argument specifically.
Wrong answers on Flaw questions follow predictable patterns. Recognising them saves significant time.
The answer describes a genuine logical flaw — just not one that is present in this argument. The LSAT will offer you a tempting flaw that sounds relevant but does not match what the argument actually did wrong. Always verify: is this the flaw in this specific argument?
Some choices accurately describe something the argument did, but describe it in a way that sounds like a criticism when it is not actually a logical error. Read carefully — does this answer actually identify a logical problem, or does it just describe a feature of the argument?
The answer describes a flaw more severe than what the argument actually commits. The argument made a moderate leap; the answer describes a complete logical collapse. These are tempting because they identify the right category of flaw but exaggerate it.
The answer describes what would be needed to strengthen or fix the argument, rather than identifying what is wrong with it. These answers look helpful rather than critical. They are always wrong on Flaw questions.
Select your answer before the explanation is revealed. Each question has a full explanation covering why the correct answer is right and why the most tempting wrong answer fails.
This is a classic causation-from-correlation flaw. The argument observes that sales increased during the same period as the advertising campaign and immediately concludes the campaign caused the increase. But the mere fact that two things happened at the same time does not establish that one caused the other. Sales could have risen because of economic conditions, competitor pricing changes, a new model launch, or any number of other factors. Answer B captures this precisely. Answer C is tempting — comparing to other companies is intuitively relevant — but the flaw in this argument is not a failure to make that comparison. The flaw is the unjustified causal inference itself.
This is a false dichotomy. The argument presents exactly two options — approval of this specific plan, or inevitable decline — as though they are the only possibilities. But there could be other development plans, different policy approaches, private investment, or other interventions that could address downtown decline. The argument has artificially restricted the available options to two. Answer B identifies this directly. Answer A is plausible on a first read but misses the point entirely — the flaw is not about the permanence or changeability of the council's decision. The flaw is the false either/or structure of the argument itself.
This is an ad hominem argument. The argument does not engage with Professor Okafor's reasoning at all — it simply notes that she has professional reasons to want arts funding increased, and uses that to dismiss her argument entirely. But even a self-interested argument can be logically correct. Her potential bias tells us to scrutinise her reasoning carefully; it does not tell us the reasoning is unsound. Answer A captures this precisely: the argument attacks the person rather than the argument. Answer B is partially related but introduces "financial interests" specifically — the argument actually attacks her professional advocacy history and committee role, which is slightly different and makes B less precise than A.
This is a more complex version of the causation flaw. The argument chains two correlations together — coffee correlates with energy, energy correlates with exercise — and leaps to a direct causal conclusion about coffee and exercise. Neither individual study established causation; both established correlation only. Even if both correlations are valid, the chain does not guarantee a direct causal relationship between coffee and exercise, and many other factors influence both energy levels and exercise habits. Answer B captures the specific structure of this flaw precisely. Answer A would be correct if the argument had directly observed coffee affecting exercise behaviour — it did not. It used two separate, indirect correlational studies, which makes B the more accurate description.
This is the "treating inability to disprove as proof" flaw. The argument's entire basis for calling the speed reduction unnecessary is that no study has conclusively proven the higher speed is more dangerous. But the absence of conclusive proof is not the same as proof of safety. Studies may not have been conducted, may have been inconclusive for methodological reasons, or may require further replication. The argument treats a gap in the evidence as positive evidence for safety, which is a logical error. Answer B captures this exactly. Answer A raises a legitimate concern — other factors beyond accident rates do matter in speed limit decisions — but it describes what the argument omits rather than identifying the logical flaw that is actually present in the reasoning.
Work through these five questions under timed conditions. Allow yourself no more than ninety seconds per question. Answers are in the key below — do not look until you have answered all five.
Flaw questions reward pattern recognition above almost everything else. The more arguments you analyse — not just practice, but actively dissect — the faster you will see the gap between premises and conclusion and name it precisely. Every argument you encounter in daily life is practice material: news articles, opinion pieces, conversations. Train yourself to ask, constantly: does this conclusion actually follow? That habit of mind is exactly what the LSAT is measuring. It is also what good legal reasoning requires.
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