Essential Guide to LSAT Logical Reasoning

Hi, this is Matt at LSAT Lab, and today's lesson is on how to master the logical reasoning section. It's a really important section type since there are twice as many sections of logical reasoning as any other section type. In today's lesson, we're going to cover the following. The role of the logical reasoning section on the LSAT. The different kinds of question types you should expect to face. in the logical reasoning section, how they make questions more or less difficult, how to use trap answers in order to eliminate wrong answers, and how to use reasoning structures to better identify the gap in the argument. So let's get started. Like every question on the LSAT, in logical reasoning there are five multiple choice answers for every question. On average, there are 25 questions per section in logical reasoning, and each section is 35 minutes per section. There are a total of four sections that are scored on the LSAT, and two of them are logical reasoning sections, which makes logical reasoning half of your total score. Here's an actual question from the logical reasoning section. For now, all we want to do is identify the different parts of the question so that we have the same vocabulary to talk about different places in the question. That initial paragraph is called the stimulus, and it's the place where we get the information on which we're going to act, whether it's a set of statements. or an argument. They're going to ask us a question based on that initial stimulus. Then we have the question stem, and the question stem is where we get our task, the thing that we need to accomplish in order to get to the correct answer. Question stem is very important because it helps us organize our work. We can organize our study around the different question types, and those will give us information both about what kinds of things to expect in the stimulus and what kinds of things to expect in the answer choices. We're always going to get five multiple choice answers, and it's our job to pick the one that best answers the question. So if we organize our work around question types, one thing we'll see is that there are a lot of different kinds of questions that they can ask, and that those questions or different question types can be grouped according to these three large families. The first family is the assumption family. 64% of all logical reasoning questions are in the assumption family. These questions measure our ability to evaluate arguments. And so what we'll be looking for is the gap or problem with the argument, the flaw in its reasoning. If we can understand what's wrong with the argument, that will be the key to success on all of these question types. One thing that we really want to be clear on when evaluating arguments is in how we judge the argument. And so there's a concept of validity and another concept of soundness. And the LSAT doesn't care about... both of these. It's really important that we get clear what the LSAT is looking for. So a valid argument is one in which the evidence proves the conclusion, 100% guaranteed. And a sound argument is one in which the evidence proves the conclusion, but the evidence is indeed true as well. The LSAT does not care about soundness. The LSAT only cares about validity. And what that means is that we don't have to worry about whether the evidence is true or isn't true. We're going to accept the evidence in these arguments, and we're going to question whether or not they established the conclusion. Our path to success in the assumption family hinges on our ability to evaluate these arguments and find the gap in the reasoning, and we want to accept the evidence but question whether the conclusion follows from it. In fact, in every single question in the assumption family, the answer to whether the argument is valid or not is that it is not valid. And if we can figure out what the gap is in the argument, that will take us to the right answer. Another important family in logical reasoning is the function family. 19% of all questions in logical reasoning belong to the function family. And these are questions that are measuring our ability to abstract from the reasoning, to understand the purpose and role and how things work within an argument. So we're really kind of slicing and dicing and understanding the mechanisms that drive arguments and the roles that claims are playing within them. And finally, there's the inference family. And 24% of all logical reasoning questions belong to this family. This is about figuring out what we know based off of what we just read. So these tend to give us statements instead of arguments and ask us to figure out what we know based off of what we just read. Now, if we look at the difficulty level of a logical reasoning section, in this section, we have the difficulty level of 25 questions. And this is from PrepTest 72, section 3. So this is a... real logical reasoning section. And these questions are weighted on a one to five point scale. You can see the difficulty level. It jumps around quite a bit, and there are different plateaus of difficulty. But each section, as you move from one logical reasoning section to another, has its own distinct curve. And so if we look at another section, prep test 76, section 2, we'll see a completely different curve, one that looks actually a little bit more challenging, and more consistently progressing in the more challenging direction. If we take all of the logical reasoning sections, from prep test 62 to 81, and we take the... average difficulty level of each question at that point in the section, we start to see a unique shape emerge. And what we're looking at here is the average difficulty trend within a logical reasoning section. There's a challenge reward curve that the LSAT likes to use, which essentially rewards students for having accomplished something that was hard. And we get two of them. So as we move past question 12 and into the early teens, we have a little bit of a reward. And as we get past question 21, 22, we start to get a little bit more reward as well. Essentially, what this is doing is there are some students who will not make it all the way through the section. And this is giving them their reward. And there are some students who will make it to the end of the section. And questions 23 to 25 are giving them their reward. So a good way to think about the difficulty level as you're moving through the section is to break it up into thirds. We can look at the first third as being the easiest third. The middle third is being a little bit more challenging and the final third is being the hardest. And the kind of mindset that's appropriate for each of these parts of the logical reasoning section is different. And by using a different mindset, it will more easily allow you to arrive at the kind of thinking that's going to get you to the right answer. So let me explain to you what I mean by that. In the first third of the section, the way you think about these questions should be driven primarily by intuition. You shouldn't overanalyze. You can use what you know about the real world, and that information will be helpful in terms of helping you come up with ideas of how to counter an argument or rebut a position. We really want to rely on our everyday experience in order to be able to move quickly through these questions. To provide an example of the kind of thinking that is intuitive, well, let's look at this argument here. That blue cars are the fastest cars on the road, therefore you should buy a blue car. That argument rests on an assumption. It's not guaranteed that you should buy a blue car, even though blue cars are the fastest cars on the road. And there are many assumptions that are possible for you to come up with. So the kind of thinking that is going to help you figure out how to attack this argument or how to help this argument is going to be based off of your understanding of the real world. So if you think about what's an assumption of this argument, what you might come up with is different than what someone else might come up with because there are many... things that are possible. So take a second, think about what's an assumption here, and then compare that idea or those ideas that you've come up with the following. One assumption would be that you should buy the fastest car on the road. That was actually never stated in the evidence. And so that recommendation that is involved in the conclusion needs to be assumed that you should actually go out and do something about blue cars being the fastest cars on the road. Or you could think about it more from a feature perspective. Is speed really the most important feature for you? Maybe, or maybe not. The assumption of this argument is that speed is more important than something like safety. But then once you get down this feature mechanism, you could actually go for a very long ways. Speed is more important than fuel efficiency or speed is more important than affordability. There are lots of features that you might prioritize over speed. And if any one of them were true, that would be a problem for this argument. So When we're thinking about how to attack the argument, we really want to be using real-world thinking, ideas that shouldn't be very academic or esoteric in nature. They should be how you would understand the argument from a real-world perspective. Once you've figured out what's wrong with the argument, then you want to use that to anticipate what an answer could sound like, and then go find that directly in the answer choices. And typically, you'll find that there's one answer choice that speaks to that idea. But as you move deeper into the section, one way in which they start to increase the difficulty level is by creating more and more answer choices that look very tempting, that look like they might actually do the trick. And so you'll find yourself tempted between two choices more and more often as you get deeper into the section. To deal with these tempting but wrong answer choices, it's very important to understand how they build trap answers, ones that will be very tempting even though they're wrong. Suppose you're looking at a question, and you've gone through and you've eliminated B and D and E, but now you're stuck between choices A, and C. And you're not quite sure which one of them is the right answer. In fact, on On your first read, they both look like they're saying the same thing. Well, to get good at logical reasoning, it's really important to be able to identify specific kinds of traps. And those traps are going to fall into three different buckets, which we'll talk about in a second here. In this example question, if we look at the difference between answer choices A and C, we'll see that they both use the word if within the sentence, but they use it at different places within it. that different placement of the word if sends the directional relationship implied by these answer choices in opposite directions. So if we look at answer choice A, the word if introduces the term decrease in profits. And that tells us that decrease in profits is the sufficient condition of a conditional relationship and that the necessary condition is that the price paid for beans actually went up. This is building an if-then relationship between two terms. It's the same two terms that are presented in answer choice C. But if we look at answer choice C and where the word if is, if is now introducing the idea that the price paid for the coffee beans is going to go up. And so what this is doing is it's reversing the direction of the relationship. So shoving if into different places within the answer choice, they've created essentially two different ideas, even though they look very, very similar at the beginning. Now, it turns out that in this case, we wanted a relationship between the price paid for beans going up and a decrease in profits. And that means that answer choice A was reversing the relationship that we were looking for. And reversal is probably the number one trap answer that you need to be on the lookout for when you're working in the logical reasoning section. There are lots of different types of trap answer patterns. They all fall into three general buckets, though. Those relating to scope, those relating to logic, and those relating to degree. Here are a couple examples of each, but there are many more for you to learn. Essentially, for each question type, there are three to five trap answer patterns that you really need to know and be aware of so that you're looking for specific things in the answer choices and are able to get rid of those tempting but wrong ones. What makes the questions in the final third of the section so challenging is that not only do we have trap answers to pay attention to, but we also have arguments that are much harder to get our heads around. Instead of talking about things like cars, they'll start talking about things like anthracosaur fossils, things that you and I typically can't relate to, and so therefore have a hard time using our intuition to understand what's wrong with the argument. And so for these arguments, we're going to use reasoning structures in order to be able to identify the gap in the reasoning. There are three types of reasoning structures that you really need to be on the lookout for when you're reading through these arguments, as well as the answer choices in order to be able to identify trap answer patterns. The reasoning structures that you really need to know about are conditional logic, causation, and comparison. The way conditional logic works is it builds together a series of conditional relationships, like if A then B, and if B then C, and it draws a conclusion from them that links them together using the transitive property. So these two would suggest that if A is true, then C is true. By understanding the argument in this manner, when there's a gap in the reasoning, we'll be able to identify it. more clearly what is that gap and what should that relationship look like between the unconnected terms. Conditional logic is a really important reasoning structure in logical reasoning. In fact, 54% of all logical reasoning questions use or rely on conditional logic. That doesn't mean that you should go out and diagram 54% of logical reasoning questions, but it does mean that at the heart of the question, or maybe on the periphery of the question, there is somewhere contained a conditional relationship that playing a role in how you're supposed to work through the question and understanding that if then idea will be super helpful, especially when you get to the harder questions. Next, we have causal reasoning structures. And a causal reasoning structure is very similar to a conditional reasoning structure in that it's building a relationship between A and B, but the connection is deeper than in a conditional relationship. Causation implies conditionality, but conditionality does not imply causation. So The connection that's implied with a causal relationship is deeper, stronger than one with conditionality. A causal relationship implies that one thing is responsible for the other, whereas conditionality simply gives you a correlation between those two events. A perfect correlation in one direction, but there's a correlation nonetheless. So in causation, A causes B, and B causes C, therefore A causes C. We can work through causal chains the same way we can work through... conditional chains. Causation plays a role in 34% of all logical reasoning questions. It's a really important reasoning structure, maybe not as important as conditional logic, but on some question types, it's the main player. And it's really important to know when you really want to be thinking within a conditional mindset. And that's typically based off of the question type. Finally, there are also comparative reasoning structures. So you might have a statement that says A is less than B, and another one that says that B is less than C. From them, we can infer that A is less than C. So we can work through comparative chains the same way we can work through causal or conditional chains. Comparison plays a role in 65% of all logical reasoning questions, making it the most important reasoning structure for you to be paying attention to. Typically, you'll see that a comparison works either by comparing two different things at a point in time, let's say the effectiveness of medication X versus the effectiveness of medication Y, two different points in time. Let's say the population of city A today versus the population of city A 10 years ago. So coming back to the overall difficulty level of the section, you can see that in the first third, you really want to be taking an intuitive approach and not overanalyzing. Don't bring in too much process and go with your intuition. As you move into the middle third of the section, you still primarily want to use your intuitive reasoning to understand the arguments and to find the gap in the reasoning that may be more true for some than for others. But you're going to find that as you look at the choices, the trap answers, in order to be able to make those eliminations, you really need to understand how they build tempting but wrong answer choices. And use those trap answer patterns to make the eliminations. And then in that last third, use reasoning structures to better understand the argument and to identify the gap in its reasoning so that you can anticipate what an answer would sound like. But even after you've gone through all that work, you're still going to need trap answers to make eliminations in the choices. So there are three keys to mastering logical reasoning. First, you need to understand argument structure. How do you identify conclusions? How do you identify evidence? How do you find opposing points? You need to be able to use keywords to help you organize arguments. Then you need to use keywords to help you identify reasoning structures and better anticipate what the missing gap would look like and use trap answer patterns to work from wrong to right through the harder questions. So that's it for today's lesson. on how to master logical reasoning, I invite you to check out these other video lessons, or visit us today at lsatlab.com.

The role of the logical reasoning section on the LSAT. The different kinds of question types you should expect to face. in the logical reasoning section, how they make questions more or less difficult, how to use trap answers in order to eliminate wrong answers, and how to use reasoning structures to better identify the gap in the argument.

So let's get started. Like every question on the LSAT, in logical reasoning there are five multiple choice answers for every question. On average, there are 25 questions per section in logical reasoning, and each section is 35 minutes per section.

There are a total of four sections that are scored on the LSAT, and two of them are logical reasoning sections, which makes logical reasoning half of your total score. Here's an actual question from the logical reasoning section. For now, all we want to do is identify the different parts of the question so that we have the same vocabulary to talk about different places in the question.

That initial paragraph is called the stimulus, and it's the place where we get the information on which we're going to act, whether it's a set of statements. or an argument. They're going to ask us a question based on that initial stimulus. Then we have the question stem, and the question stem is where we get our task, the thing that we need to accomplish in order to get to the correct answer.

Question stem is very important because it helps us organize our work. We can organize our study around the different question types, and those will give us information both about what kinds of things to expect in the stimulus and what kinds of things to expect in the answer choices. We're always going to get five multiple choice answers, and it's our job to pick the one that best answers the question.

So if we organize our work around question types, one thing we'll see is that there are a lot of different kinds of questions that they can ask, and that those questions or different question types can be grouped according to these three large families. The first family is the assumption family. 64% of all logical reasoning questions are in the assumption family.

These questions measure our ability to evaluate arguments. And so what we'll be looking for is the gap or problem with the argument, the flaw in its reasoning. If we can understand what's wrong with the argument, that will be the key to success on all of these question types. One thing that we really want to be clear on when evaluating arguments is in how we judge the argument.

And so there's a concept of validity and another concept of soundness. And the LSAT doesn't care about... both of these.

It's really important that we get clear what the LSAT is looking for. So a valid argument is one in which the evidence proves the conclusion, 100% guaranteed. And a sound argument is one in which the evidence proves the conclusion, but the evidence is indeed true as well.

The LSAT does not care about soundness. The LSAT only cares about validity. And what that means is that we don't have to worry about whether the evidence is true or isn't true. We're going to accept the evidence in these arguments, and we're going to question whether or not they established the conclusion.

Our path to success in the assumption family hinges on our ability to evaluate these arguments and find the gap in the reasoning, and we want to accept the evidence but question whether the conclusion follows from it. In fact, in every single question in the assumption family, the answer to whether the argument is valid or not is that it is not valid. And if we can figure out what the gap is in the argument, that will take us to the right answer. Another important family in logical reasoning is the function family.

19% of all questions in logical reasoning belong to the function family. And these are questions that are measuring our ability to abstract from the reasoning, to understand the purpose and role and how things work within an argument. So we're really kind of slicing and dicing and understanding the mechanisms that drive arguments and the roles that claims are playing within them. And finally, there's the inference family. And 24% of all logical reasoning questions belong to this family.

This is about figuring out what we know based off of what we just read. So these tend to give us statements instead of arguments and ask us to figure out what we know based off of what we just read. Now, if we look at the difficulty level of a logical reasoning section, in this section, we have the difficulty level of 25 questions.

And this is from PrepTest 72, section 3. So this is a... real logical reasoning section. And these questions are weighted on a one to five point scale. You can see the difficulty level. It jumps around quite a bit, and there are different plateaus of difficulty.

But each section, as you move from one logical reasoning section to another, has its own distinct curve. And so if we look at another section, prep test 76, section 2, we'll see a completely different curve, one that looks actually a little bit more challenging, and more consistently progressing in the more challenging direction. If we take all of the logical reasoning sections, from prep test 62 to 81, and we take the... average difficulty level of each question at that point in the section, we start to see a unique shape emerge. And what we're looking at here is the average difficulty trend within a logical reasoning section.

There's a challenge reward curve that the LSAT likes to use, which essentially rewards students for having accomplished something that was hard. And we get two of them. So as we move past question 12 and into the early teens, we have a little bit of a reward. And as we get past question 21, 22, we start to get a little bit more reward as well.

Essentially, what this is doing is there are some students who will not make it all the way through the section. And this is giving them their reward. And there are some students who will make it to the end of the section.

And questions 23 to 25 are giving them their reward. So a good way to think about the difficulty level as you're moving through the section is to break it up into thirds. We can look at the first third as being the easiest third. The middle third is being a little bit more challenging and the final third is being the hardest. And the kind of mindset that's appropriate for each of these parts of the logical reasoning section is different.

And by using a different mindset, it will more easily allow you to arrive at the kind of thinking that's going to get you to the right answer. So let me explain to you what I mean by that. In the first third of the section, the way you think about these questions should be driven primarily by intuition.

You shouldn't overanalyze. You can use what you know about the real world, and that information will be helpful in terms of helping you come up with ideas of how to counter an argument or rebut a position. We really want to rely on our everyday experience in order to be able to move quickly through these questions. To provide an example of the kind of thinking that is intuitive, well, let's look at this argument here. That blue cars are the fastest cars on the road, therefore you should buy a blue car.

That argument rests on an assumption. It's not guaranteed that you should buy a blue car, even though blue cars are the fastest cars on the road. And there are many assumptions that are possible for you to come up with.

So the kind of thinking that is going to help you figure out how to attack this argument or how to help this argument is going to be based off of your understanding of the real world. So if you think about what's an assumption of this argument, what you might come up with is different than what someone else might come up with because there are many... things that are possible.

So take a second, think about what's an assumption here, and then compare that idea or those ideas that you've come up with the following. One assumption would be that you should buy the fastest car on the road. That was actually never stated in the evidence. And so that recommendation that is involved in the conclusion needs to be assumed that you should actually go out and do something about blue cars being the fastest cars on the road. Or you could think about it more from a feature perspective.

Is speed really the most important feature for you? Maybe, or maybe not. The assumption of this argument is that speed is more important than something like safety. But then once you get down this feature mechanism, you could actually go for a very long ways. Speed is more important than fuel efficiency or speed is more important than affordability.

There are lots of features that you might prioritize over speed. And if any one of them were true, that would be a problem for this argument. So When we're thinking about how to attack the argument, we really want to be using real-world thinking, ideas that shouldn't be very academic or esoteric in nature. They should be how you would understand the argument from a real-world perspective.

Once you've figured out what's wrong with the argument, then you want to use that to anticipate what an answer could sound like, and then go find that directly in the answer choices. And typically, you'll find that there's one answer choice that speaks to that idea. But as you move deeper into the section, one way in which they start to increase the difficulty level is by creating more and more answer choices that look very tempting, that look like they might actually do the trick. And so you'll find yourself tempted between two choices more and more often as you get deeper into the section. To deal with these tempting but wrong answer choices, it's very important to understand how they build trap answers, ones that will be very tempting even though they're wrong.

Suppose you're looking at a question, and you've gone through and you've eliminated B and D and E, but now you're stuck between choices A, and C. And you're not quite sure which one of them is the right answer. In fact, on On your first read, they both look like they're saying the same thing.

Well, to get good at logical reasoning, it's really important to be able to identify specific kinds of traps. And those traps are going to fall into three different buckets, which we'll talk about in a second here. In this example question, if we look at the difference between answer choices A and C, we'll see that they both use the word if within the sentence, but they use it at different places within it.

that different placement of the word if sends the directional relationship implied by these answer choices in opposite directions. So if we look at answer choice A, the word if introduces the term decrease in profits. And that tells us that decrease in profits is the sufficient condition of a conditional relationship and that the necessary condition is that the price paid for beans actually went up.

This is building an if-then relationship between two terms. It's the same two terms that are presented in answer choice C. But if we look at answer choice C and where the word if is, if is now introducing the idea that the price paid for the coffee beans is going to go up. And so what this is doing is it's reversing the direction of the relationship. So shoving if into different places within the answer choice, they've created essentially two different ideas, even though they look very, very similar at the beginning.

Now, it turns out that in this case, we wanted a relationship between the price paid for beans going up and a decrease in profits. And that means that answer choice A was reversing the relationship that we were looking for. And reversal is probably the number one trap answer that you need to be on the lookout for when you're working in the logical reasoning section.

There are lots of different types of trap answer patterns. They all fall into three general buckets, though. Those relating to scope, those relating to logic, and those relating to degree.

Here are a couple examples of each, but there are many more for you to learn. Essentially, for each question type, there are three to five trap answer patterns that you really need to know and be aware of so that you're looking for specific things in the answer choices and are able to get rid of those tempting but wrong ones. What makes the questions in the final third of the section so challenging is that not only do we have trap answers to pay attention to, but we also have arguments that are much harder to get our heads around. Instead of talking about things like cars, they'll start talking about things like anthracosaur fossils, things that you and I typically can't relate to, and so therefore have a hard time using our intuition to understand what's wrong with the argument. And so for these arguments, we're going to use reasoning structures in order to be able to identify the gap in the reasoning.

There are three types of reasoning structures that you really need to be on the lookout for when you're reading through these arguments, as well as the answer choices in order to be able to identify trap answer patterns. The reasoning structures that you really need to know about are conditional logic, causation, and comparison. The way conditional logic works is it builds together a series of conditional relationships, like if A then B, and if B then C, and it draws a conclusion from them that links them together using the transitive property. So these two would suggest that if A is true, then C is true. By understanding the argument in this manner, when there's a gap in the reasoning, we'll be able to identify it.

more clearly what is that gap and what should that relationship look like between the unconnected terms. Conditional logic is a really important reasoning structure in logical reasoning. In fact, 54% of all logical reasoning questions use or rely on conditional logic. That doesn't mean that you should go out and diagram 54% of logical reasoning questions, but it does mean that at the heart of the question, or maybe on the periphery of the question, there is somewhere contained a conditional relationship that playing a role in how you're supposed to work through the question and understanding that if then idea will be super helpful, especially when you get to the harder questions. Next, we have causal reasoning structures.

And a causal reasoning structure is very similar to a conditional reasoning structure in that it's building a relationship between A and B, but the connection is deeper than in a conditional relationship. Causation implies conditionality, but conditionality does not imply causation. So The connection that's implied with a causal relationship is deeper, stronger than one with conditionality. A causal relationship implies that one thing is responsible for the other, whereas conditionality simply gives you a correlation between those two events. A perfect correlation in one direction, but there's a correlation nonetheless.

So in causation, A causes B, and B causes C, therefore A causes C. We can work through causal chains the same way we can work through... conditional chains. Causation plays a role in 34% of all logical reasoning questions.

It's a really important reasoning structure, maybe not as important as conditional logic, but on some question types, it's the main player. And it's really important to know when you really want to be thinking within a conditional mindset. And that's typically based off of the question type.

Finally, there are also comparative reasoning structures. So you might have a statement that says A is less than B, and another one that says that B is less than C. From them, we can infer that A is less than C. So we can work through comparative chains the same way we can work through causal or conditional chains.

Comparison plays a role in 65% of all logical reasoning questions, making it the most important reasoning structure for you to be paying attention to. Typically, you'll see that a comparison works either by comparing two different things at a point in time, let's say the effectiveness of medication X versus the effectiveness of medication Y, two different points in time. Let's say the population of city A today versus the population of city A 10 years ago. So coming back to the overall difficulty level of the section, you can see that in the first third, you really want to be taking an intuitive approach and not overanalyzing. Don't bring in too much process and go with your intuition.

As you move into the middle third of the section, you still primarily want to use your intuitive reasoning to understand the arguments and to find the gap in the reasoning that may be more true for some than for others. But you're going to find that as you look at the choices, the trap answers, in order to be able to make those eliminations, you really need to understand how they build tempting but wrong answer choices. And use those trap answer patterns to make the eliminations. And then in that last third, use reasoning structures to better understand the argument and to identify the gap in its reasoning so that you can anticipate what an answer would sound like.

But even after you've gone through all that work, you're still going to need trap answers to make eliminations in the choices. So there are three keys to mastering logical reasoning. First, you need to understand argument structure.

How do you identify conclusions? How do you identify evidence? How do you find opposing points? You need to be able to use keywords to help you organize arguments. Then you need to use keywords to help you identify reasoning structures and better anticipate what the missing gap would look like and use trap answer patterns to work from wrong to right through the harder questions.

So that's it for today's lesson. on how to master logical reasoning, I invite you to check out these other video lessons, or visit us today at lsatlab.com.

Transcript for:Essential Guide to LSAT Logical Reasoning

Transcript for:
Essential Guide to LSAT Logical Reasoning