Not every argument is convincing. In fact, many arguments have something wrong with them. The LSAT-makers place the flaws there to test your ability to spot them. As a lawyer, you have to spot your opponents’ bad arguments so you can attack them and spot bad arguments in your own work so you can fix them.

These problems are a bit more complicated than questions that simply ask you to draw a conclusion. First you find the conclusion, then you figure out how the author reached it, and finally you determine what’s wrong with that reasoning process.

Take a look at some examples of spot-the-flaw questions:

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

  • The reasoning above is flawed because it fails to recognize that…

  • The argument is vulnerable to criticism on which one of the following grounds?

  • The reasoning in the argument is flawed because the argument fails to take into account that...

  • The argument is questionable because it fails to consider…

Occasionally, the LSAT asks you to find the flaw in a formal argument. Usually the author draws a faulty conclusion by confusing a sufficient condition with a necessary one. For example, an argument may fallaciously conclude that because only girls wear pink and Jane is a girl, Jane must be wearing pink.

Notice that if the first premise stated that all girls wear pink, the conclusion that Jane is wearing pink would be justified. The majority of finding-the-flaw questions, however, concern informal arguments and are easier to answer when you’re familiar with informal fallacies. Some of the informal fallacies most commonly tested on the LSAT are these:

  • Fallacies of relevance occur when the conclusion isn’t relevant to the premises offered to support it.

    • An appeal to force specifies that you better believe a conclusion is true or you’ll suffer harm.

    • The bandwagon approach requires you to accept a conclusion because everybody else does.

    • The red herring introduces a premise that has nothing to do with the argument and then bases the conclusion on that irrelevant point.

    • An ad hominem attack opposes another’s argument by attacking the person rather than the conclusion’s reasonability.

  • Fallacies of weak induction occur when the premises don’t adequately support the conclusion.

    • An appeal to authority is fallacious when the authority used to support a claim isn’t an expert in the argument’s subject.

    • A hasty generalization occurs when the sample size provided to support a claim is inadequate.

  • Fallacies of ambiguity use unclear or undefined meanings.

  • Fallacies of presumption occur when someone’s claim presumes an unsubstantiated truth.

    • Circular reasoning occurs when the premise used to support a conclusion is the conclusion itself.

    • A complex question is a question presented in such a way that you can’t answer it without implicating yourself.

    • A false dichotomy occurs when an argument provides only two options, provides evidence to reject one of those options, and then concludes that the other option is the only viable truth without recognizing that other options exist.

  • Fallacies of analogy result from comparing entities that aren’t sufficiently similar to warrant a comparison. They may also occur when one claims that because the parts of a whole are a certain way, the whole is also that way, or because a whole is a certain way, the parts individually are also that way.

Watch for these informal fallacies when you approach a question that asks you to find the flaw, such as the following example.

Some southern towns have quaint downtown areas, and some southern towns have small colleges. Therefore, some southern towns with small colleges also have quaint downtown areas.

The reasoning in the argument is flawed because the argument

  • (A)implies a definite causal relationship from a coincidence that could be explained in other ways

  • (B)contains a premise that cannot be true unless the conclusion is known to be true

  • (C)employs the word “quaint” to mean two different things

  • (D)fails to acknowledge that one group could have members in common with each of two other groups without those other two groups sharing any members in common

  • (E)mistakes towns that have quaint downtown areas for towns that have small colleges

Your first step is to read the question. It asks you to figure out what’s wrong with the argument’s reasoning. Now read the argument. It concludes that because some southern towns have quaint downtowns and some have small colleges, some have both. This sounds like a fallacy of analogy.

The problem with the argument’s conclusion is that it assumes overlap between two sets (“southern towns with quaint downtown areas” and “southern towns with small colleges”) that don’t necessarily have to overlap. It’s entirely possible that the two sets of towns aren’t similar at all and that no town has both a quaint downtown and a small college.

Now read through the answers, looking for a choice that suggests a problem with the analogy. Choice (A) is wrong because no causal relationship is implied. Choice (B) is wrong because no premise of the argument depends on the conclusion; in other words, the first statement can stand on its own without the conclusion.

Choice (C) is wrong because the word “quaint” is used the same way both times to describe downtown areas. Choice (D) looks correct; the argument does illogically suppose that because one group (southern towns) has members in common with two other groups (towns with quaint downtown areas and towns with small colleges), those two latter groups must also share members.

Choice (E) is wrong because the argument doesn’t confuse the two types of towns with each other; it keeps them distinct while reaching the erroneous conclusion. Choice (D) is the best answer.