What’s Tested on LSAT Logical Reasoning

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What's Tested on LSAT Logical Reasoning

More than any other section of the test, the LSAT Logical Reasoning section has a clear mandate that directly pertains to your future as a law student: to make sure you can understand the ins and outs of argumentation. For that reason, one of my favorite LSAT Logical Reasoning tips—indeed, one of the first LSAT Logical Reasoning tips I share with all of my students—is to think of the Logical Reasoning section not as a hurdle you have to jump to get to law school, but as part of your essential preparation for law school.

What you learn from LSAT Logical Reasoning will carry you through your legal education and beyond. Being able to precisely understand what you read, to point out flaws in persuasive arguments, and to draw conclusions that must be true, not conclusions that could be true: these are skills that are necessary far beyond the legal profession. Forgive me my soapbox, but these are the skills we all must possess in order to have an informed citizenry, and yet, maddeningly, unless you took philosophy in college, chances are you haven’t done much of this kind of work.

LSAT Logical Reasoning Tests Argument Structure

Each of the LSAT Logical Reasoning sections will feature 25 or 26 short pieces of text. Each is between two and four sentences long on average. For each short piece of text, you’ll answer a question. Some questions ask you to describe the text. Others ask you to manipulate it. Still others ask you to think about what the text implies. Most of those short pieces of text are arguments.

So, let’s start out by defining what we, and the LSAT, mean by an argument. An argument is a statement, or a combination of statements, that uses evidence to support a claim. Another word for a piece of evidence that you’ll see a lot during your LSAT prep is “premise.” Don’t be intimidated: a premise is just a piece of evidence. The claim that is supported by the evidence is the argument’s conclusion.

Most questions that ask you to describe the argument will ask you to pick out the argument’s conclusion, or to identify the role that a given piece of text serves. The most challenging ones, however, will ask you to describe the entire argument structure abstractly.

LSAT Logical Reasoning Tips for Mastering Argument Structure

  • Look for keywords. Words such as thus, therefore, hence, and consequently tell you that you’re looking at a conclusion. Words such as because, for, and since tell you that you’re looking at a premise.
  • Break down every argument. No matter what the task of the question, you’ll always need to know the argument’s conclusion and it’s premise(s).
  • Find the conclusion first. It’s usually easier to spot, and you can work backwards from there to identify the premises.

LSAT Logical Reasoning Tests Assumptions

We told you already that most questions on LSAT Logical Reasoning present you with a short argument. What we didn’t tell you was that the vast majority of these arguments are pretty bad. How do you tell a good argument from a bad one? Well, in a good argument, the premises prove the conclusion. In a bad argument, they don’t.

Another way of saying that is that a bad argument rests on at least one assumption: something that would need to be true for the argument to be good, but that isn’t established by the argument. Consider these two examples:

  1. Geckos are reptiles. Therefore, geckos are cold-blooded.
  2. Geckos are reptiles. All reptiles are cold-blooded. Therefore, geckos are cold-blooded.

Argument 1 might look good at first. But Argument 1 only makes sense if we bring in outside knowledge about reptiles, namely the fact that they’re cold-blooded. In LSAT-speak, we’d say that Argument 1 assumes reptiles are cold-blooded, and is therefore a bad argument.

Argument 2, on the other hand, states that fact explicitly. You don’t need to assume anything for the argument to make sense, and so it’s a good argument.

LSAT Logical Reasoning Tips for Mastering Assumptions

  • If a question asks you to strengthen, weaken, support, or point out a flaw in an argument, that argument definitely rests on at least one assumption. After breaking the argument down into premise(s) and conclusion, try to figure out what the argument assumes.
  • If a question asks you to identify the conclusion, describe the role that certain text plays, or describe the point at issue between two speakers, assumptions probably aren’t relevant. Don’t agonize over figuring out whether those arguments rest on assumptions. Just stick to the task of the question itself.
  • Assumptions come in two flavors: Bridge Assumptions and Defender Assumptions.
  • Bridge Assumptions help you bridge the gap between the concepts in the premises and the concepts in the conclusion. In the example above, Argument 1 rested on a Bridge Assumption that bridges the gap between the reptiles discussed in the premise and concept of cold-bloodedness discussed in the conclusion.
  • Defender Assumptions defend against a possible objection to the argument. An example of a Defender Assumption for the gecko argument could be “the argument assumes that geckos aren’t mammals.”
  • Some assumptions, when added to the argument, make the argument a good argument. “All reptiles are cold-blooded” is an example of this. We call these Sufficient Assumptions, and there’s a whole question type devoted to finding them.
  • Other assumptions, when added to the argument, don’t go far enough to make the argument good. “Geckos aren’t mammals” is an example of this. Does it improve the argument? Sure. But it doesn’t make it airtight. We call these Necessary Assumptions, and as you might have predicted, they too have their own question type.

LSAT Logical Reasoning Tests Flaws

A concept that’s intimately related to assumptions in LSAT Logical Reasoning is the concept of flaws. In fact, every flaw could be described as an assumption, and every assumption is a kind of flaw. But there are certain types of flaws in reasoning that come up over and over in LSAT Logical Reasoning. They’re worth exploring in their own right.

Of the questions that ask you to identify a flaw, about half will present the flaw as an assumption. The other half will give you a flaw with a name. Now, there are plenty of lists out there, some with literally hundreds of flaws, but LSAT Logical Reasoning deals with a core set of flaws that is (mercifully!) much smaller.

Conditional Logic flaws: These flaws deal with “if/then” statements and their variations. If you’re in Brooklyn, you’re in New York. But if you’re in New York, that doesn’t necessarily mean you’re in Brooklyn. The takeaway? You can’t simply reverse an “if/then” statement. Any argument that tries to contains a Conditional Logic flaw. Similarly, we also can’t say that if you’re not in Brooklyn, you’re not in New York. You can’t simply negate an “if/then” statement either, which is the second most common Conditional Logic flaw.

Causation flaws: Any time an LSAT Logical Reasoning question deals with cause and effect, chances are high that the question exhibits a causation flaw. The most common among these is confusing a correlation between two things for a causal relationship between things. I aced the LSAT after barely sleeping the night before. But that doesn’t mean that my lack of sleep helped me ace the test.

Sampling flaws: When LSAT Logical Reasoning questions deal with data, there’s often a Sampling flaw lurking in the argument, because remember: LSAT arguments are overwhelmingly bad! The most common Sampling flaw is using a sample that isn’t a good representation of the group the conclusion deals with. Consider this argument: Those college graduates who have taken the LSAT demonstrate considerable logical prowess. Thus, our colleges must be doing a great job at teaching logic. Is the sample in that argument, LSAT takers, representative of college graduates generally? Nope. LSAT takers are a highly selective group. What’s more, they’re particularly unrepresentative with respect to their logical prowess, as LSAT takers have likely spent a great deal of time studying logic whereas the typical college grad likely has not.

Comparative flaws: If an LSAT Logical Reasoning question makes a comparison, oftentimes it will be a bad one. This is particularly true if the comparison is an analogy. Just because two things are similar in one respect, doesn’t mean they’re similar in another respect. And just because two things are different in one way doesn’t mean they’re different in another way.

LSAT Logical Reasoning Tips for Mastering Flaws

  • Flaws are one of the few things you can (and should!) memorize on the LSAT Logical Reasoning section. The list above isn’t exhaustive, so check out a more complete list before you embark on that process.
  • Flaws are exhibited and flaws are described. To master flaws, you need to be able to do both! That means recognizing flaws in arguments and recognizing when the common flaws are described by answer choices.
  • Look for flaws everywhere! The LSAT Logical Reasoning section isn’t the only place to find flaw fodder (try saying that five times fast). Cable news shows, click-bait articles, and your friends’ social media posts are all full of fallacies (we know, we’ve seen them). Looking for flaws in outside sources will deepen your understanding of them and help you spot them more reliably on test day.
  • Don’t pick the duds. There are two flaws that show up in a ton of answer choices but are almost never right: self-contradiction and circular reasoning. Why? Because it’s hard to write an argument that exhibits one of these flaws without being totally obvious. If an argument says two things that can’t both be true (self-contradiction), it’s pretty hard to miss. Same goes for an argument whose conclusion is logically equivalent to its premise (circular reasoning).

LSAT Logical Reasoning Tests Inferences

If a question on one of the LSAT Logical Reasoning sections doesn’t give you an argument, there’s a good chance that your task will be to come up with an inference. An inference is something that isn’t explicitly stated, but that could be concluded from the statements given. For example, from the statements “If you’re in Brooklyn, you’re in New York” and “Laura’s not in New York,” we can infer that I’m also not in Brooklyn. (If that’s confusing to you, it’s time to brush up on your conditional logic!)

LSAT Logical Reasoning Tips for Mastering Inferences

  • Some Inference questions will ask you for something that must be true. These answers must be 100% provable.
  • Other Inference questions will ask you which answer is most strongly supported. These don’t have to be 100% provable, but they have to be pretty close.

What’s Tested on LSAT Logical Reasoning: Bringing it All Together

Because there are 2 scored LSAT Logical Reasoning sections on every test, this is a section that should demand a lot of your attention as you prepare! If you look at an LSAT Logical Reasoning section, you might be struck by just how many different things the questions will ask you to do. It’s easy for that diversity to overwhelm you. But there’s more that unites LSAT Logical Reasoning than divides it. Think of breaking down arguments, spotting assumptions, calling out flaws, and making inferences as through-currents that inform the section across question type and task.

Final LSAT Logical Reasoning Tips

  • Try reading the question before the argument or facts. This will tell you whether there will be an argument to break down, and if so, whether you should be trying to spot assumptions and flaws.
  • If you have to reread the question before tackling the answer choices, that’s okay. Even though it takes an extra few seconds, the payoff of knowing how to approach the text is worth it.
  • Before you look at the answers, try to predict a right answer in your head. This process, called prephrasing, forces you to interact with the question on a different level. When done successfully, it deepens your knowledge of the test. But when done unsuccessfully, it alerts you to the fact that you aren’t fully understanding what you’re reading or what you’re being asked to do.
  • When you’re analyzing answer choices, rely on process of elimination. Reading an answer and asking yourself “Could this be right?” makes it more likely that you’ll end up with a bunch of answers you like. On the other hand, asking yourself “Can I find a concrete reason this answer is wrong?” makes you more likely to eliminate wrong answers and narrow it down to the right one.
  • If you can’t articulate a concrete reason an answer is wrong, put a star by it. Come back to it later and figure out why to give it the axe.
  • The hardest questions in an LSAT Logical Reasoning section are between 15 and 22.
  • If you’re looking for a top score, push your pace through earlier questions to give yourself ample time to dig into those harder ones.
  • If LSAT Logical Reasoning isn’t your strong suit, invest more time into earlier questions that are more likely to be in your wheelhouse, and the final 2 questions which are usually of medium difficulty.
  • The hard questions aren’t worth more than the easy ones. If it stumps you, ditch it before it eats up too much of your time.
  • How much time you spend per question is personal, but for those looking for a top score, trying to do the first 15 questions in 15 minutes is a good goal. Start by trying the first five in five, then the first ten in ten. Work your way up to 15 in 15.
  • Don’t waffle. If you have it down to two answers and can’t figure out which one is right, try to identify the difference between them, then think about that difference as you reread the argument or facts one last time. The difference is what will make one right (assuming you have it down to the right answer and a wrong answer!) and the other wrong.

Don’t stop here! We’ve got loads of great material to help you prep for the LSAT Logical Reasoning section. Check out our free resources, our books, our self-study program, or try a class for free! ?


Laura Damone is a Manhattan Prep instructor based in San Francisco, CA. She fell for the LSAT while getting her undergrad degree and has now taught LSAT classes at more than 20 universities around the country. When she’s not teaching, learning, or publishing her work, she can be found frolicking in the redwoods and exploring the Pacific coast. Check out Laura’s upcoming LSAT courses here!

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