LSAT Flaw Questions: The Reasoning Errors Worth Knowing Cold

A flaw question gives you an argument and asks which answer describes an error in its reasoning. The answer choices are usually written in abstract terms, such as 'takes for granted that' or 'fails to consider the possibility that', so you have to match a general description to the specific argument.

LSAC points out that you do not need to know technical names like ad hominem to answer LR questions. Names are still handy as private shorthand, but what gets you the point is being able to say, in plain words, why the conclusion does not follow from the evidence. Before reading the choices, try to finish the sentence: the argument ignores the possibility that...

Flaw answer choices use generic language on purpose, and reading them slowly is part of the skill. A choice such as 'presumes that because two phenomena occur together, one must cause the other' is the correlation flaw. A choice about treating 'something required for an outcome as enough to bring it about' describes the necessary-versus-sufficient mix-up. One that says the argument 'draws a general conclusion from cases that may not be typical' is a sampling problem.

Practice by rewriting each abstract choice in concrete terms that fit the argument in front of you. If a choice says the argument overlooks an alternative explanation, name that alternative. If you cannot name one, the choice probably does not fit. This habit also protects you against choices that contain a real flaw description but point at parts of the argument that do not exist.

Example: 'Neighborhoods with more coffee shops have higher average home prices. So if the city wants to raise property values in the east side, it should encourage new coffee shops to open there.'

The argument notices two things occurring together and concludes one produces the other. It ignores that a third factor, such as household income, could drive both, and that the direction could be reversed, with wealthier areas attracting coffee shops. When you see a conclusion about what causes what, ask whether the evidence shows only that two things tend to go together.

Example: 'Every finalist for the architecture prize submitted a scale model. Lena submitted a scale model, so she will be a finalist.'

Submitting a model is required to be a finalist, but the argument treats it as enough to guarantee becoming one. The reverse mistake also appears: 'Anyone who finishes the marathon receives a medal. Omar did not finish, so he did not receive a medal.' Finishing is sufficient for a medal, but the argument treats it as the only route. Look for words like only, requires, every, and whenever, and check whether the argument runs the condition in the direction the premise actually supports.

Example: 'At the regional gardening expo, 82 percent of visitors we surveyed said the county should fund more community greenhouses. Clearly, most county residents want that funding.'

People who attend a gardening expo are not typical residents on this question. The sample may be large, but it is drawn from a group likely to hold a particular view. Sampling flaws also appear when a sample is too small, when respondents chose themselves, or when survey questions were worded to push one answer. Ask whether the group studied looks like the group the conclusion is about.

Example: 'Each player on the new volleyball team was an all-star at her previous school. Therefore the team will be the strongest in the conference.'

Qualities of individual parts do not automatically belong to the whole. Excellent players may not play well together. The mirror error moves from whole to part: 'The orchestra is the best in the state, so its second oboist must be one of the best oboists in the state.' Watch for conclusions that shift between a group and its members without justification.

Example: 'The review board's rulings are always fair, because the board would never issue an unfair ruling.'

The support restates the conclusion rather than giving independent reason to accept it. On the test, circularity is usually disguised by rewording, so the premise and conclusion look different on the surface. A good check is to ask whether anyone who doubted the conclusion would find the premise any more convincing. If not, the argument assumes what it sets out to prove.

Example: 'Councilmember Reyes argues that the bus routes should be redrawn. But Reyes drives to work every day, so her proposal can be ignored.'

The argument rejects a position because of something about the person advancing it, not because of any problem with the reasons given for the position. A personal fact might raise questions about motive, but it does not show the proposal is wrong. Related versions reject a claim because its supporters have been wrong before, or accept one because a popular figure endorses it.

Several other patterns come up often enough to learn. Each of the examples here is invented.

Keep a running list of the flaws behind your practice misses, and after each LawHub practice test, count them. Most people find two or three flaws account for the bulk of their errors. Drill those by writing your own short arguments that commit each one, because producing a flaw teaches you its shape faster than reading about it.

When reviewing answer choices, test each description against the argument literally. A choice can name a real flaw that simply is not present in this argument, which is the most common trap on these questions. RetakePrep's daily drills draw 20 questions from your three weakest families and explain each answer as you go, which suits this kind of repeated recognition practice.