When Should You Diagram LSAT Logical Reasoning Questions?

In this post, next in our series on logical reasoning basics, we cover the all-important topic of when you should diagram and when you shouldn’t on the LSAT logical reasoning section. Follow this advice to get a slight edge that may earn you extra points on test day.

Diagramming Basics

Right away we should draw a distinction between diagramming, which is generally a means of attacking formal logic that you see in the questions, and making other notes on the questions. For example it is common to mark the conclusion of the argument or underline a difficult sentence that you think will be critical for answering the question; this is not what this article discusses.

Diagramming is different, and involves a system of writing out logical relationships that are frequently tested on the LSAT. Let’s look at a sentence that expresses a logical relationship, so you know the kinds of things that you may wish to diagram when doing problems. If you have done this stuff already in some prep materials, skip this next section.

Formal Logic Example: Conditional Statements

The following sentence can be expressed in terms of formal logic:

If wild blueberries are growing then it must be summer.

The above sentence contains what you may have heard referred to as necessary and sufficient conditions. ‘Blueberries growing’ is a sufficient condition, meaning that if you take the above sentence as true, then knowing that blueberries are growing is sufficient to know that it is summer. Also, if the sentence is taken as true, then summer is a necessary condition, meaning it is necessary that is be summer for blueberries to grow.

This sentence can be diagrammed as follows:

WB —–> S

We also know from the above sentence that if it is not summer then wild blueberries are not growing. In logic this is called a contrapositive, and it can be diagrammed as follows:

S ——–> WB

Not too hard right? The problem is the LSAT throws several of these statements at you at once and asks you to make connections between them, so it’s often hard to keep track of what’s going on without diagramming.

Learning a Diagramming Method

To get a full lesson in logic for the LSAT I recommend you get a prep book that covers this material and gives you plenty of practice diagramming conditional statements.

When I started my prep I was using the diagramming system that I had learned in my undergrad logic class. Those techniques were slower so if you have already learned logic that way, forget using those symbols on the LSAT. That said, it was still worth taking a logic course. It gives you a big head start in thinking the way you have to think on the LSAT.

The methods taught by most prep companies are going to be more effective for the LSAT than formal diagramming notation. I personally recommend the methods taught by Powerscore in their Logical Reasoning Bible. I tried almost everything out there early in my prep and their method was the fastest to use and the most simple.

Remember that the most important thing is that you pick an effective diagramming strategy and stick with it. This is most important in diagramming logic games, which is more complex, but it’s also important on logical reasoning.

When to Diagram

Knowing when to diagram and when you will be fine just laying off it is one of hardest aspects of mastering the logical reasoning section. Some people are of the opinion that diagramming  is very fast and that it isn’t too harmful to diagram a lot when it isn’t necessary. I disagree. The LSAT is about gaining precious seconds anywhere you can, because they add up.

The key to knowing when to diagram and how much is practice, practice, practice. Practice gives you get a feel for what kinds of questions you can get away with not diagramming or with less diagramming. Sorry, but there just aren’t many shortcuts in LSAT practice. We’ll give some more tips though to get help you get started on the right track:

Sometimes it’s easy to know that you should diagram. If you see very straightforward conditional logic on a logical reasoning question but it looks like a lot to keep straight in your head, go ahead and diagram it. However, often the LSAT will throw problems at you that look like they should be diagrammed extensively, when in reality there an important inference that you can make just staring you right in the face. With that inference you can just answer the question right and save time.

The trick is knowing exactly what YOU as a test taker can and can’t get away with.

Let’s take a look at a fairly hard question where some people might diagram a lot and others might be comfortable with less or skipping it entirely:

Most pro athletes are happy athletes, and most pro athletes go to training camp. Further, all athletes who go to training camp are trained to exhaustion.

Which one of the following can be properly inferred from the statements above?

1) Most athletes trained to exhaustion are happy athletes.
2) Some unhappy athletes go to training camp
3) All athletes trained to exhaustion are pro athletes
4)  Some happy athletes are trained to exhaustion
5) All pro athletes are trained to exhaustion

Now you can sit there working out the diagram for this problem. A common way to do it would be to write:

PA most HA

PA most TC

TC —–> TTE

Now, the diagram here may help you make the important inference needed to solve the question. Did you spot it? ‘Most’ in this context means more than half. Since we know that most pro athletes are happy and we know most pro athletes go to training camp, that means there must be some overlap, meaning that some happy athletes go to training camp. From that, we can make the further inference that some happy athletes are trained to exhaustion (since any athlete who goes to training camp is trained to exhausted).

These inferences in diagram form:

HA some TC (some happy athletes go to training camp)

HA some TTE (some happy athletes are trained to exhaustion)

If we look to the answer choices, we see that the correct answer is this second inference, answer choice 4.

Now this mechanical method of approaching the problem is going to work, and will help you solve it and also even more difficult questions. However, I don’t think that an experienced master of logical reasoning does all this diagramming out before going to the answer choices.

This is because with long prep they have developed the intuition to see that there is really just one hard inference here, which is spotting that overlap in the first two premises whereby there has to be some happy athletes that go to training camp. Once an experienced test taker sees something like that in a logical reasoning, he or she knows that it’s very likely to be tested because it’s the most difficult inference to make. They may then either diagram that one key inference or possibly they just go straight to the answer choices and look for it or some further simple inference based on it. As it turns out, the correct answer is a further simple inference.

I’ll repeat that I think most good test takers here just diagram either that one inference, just the second two (some happy athletes go to training camp, some happy athletes are trained to exhaustion), or they just don’t diagram at all.

If this seems like an impossible mental feat right now, don’t worry, long prep will help you make these inferences quicker and help and develop the intuition needed to know when you can just jump straight to the answer choices.

Definitely do check out resources that specifically help build this skill. The Logical Reasoning Bible has a lot of training materials that help you make these kinds of inferences. It also drills you extensively on just the kinds of questions that require this diagramming.

Don’t expect to be doing these mental gymnastics perfectly at first. It comes with practice. Here’s what you should do when starting out:

Diagram Too Much at First

As you start prepping it is best to just attempt to diagram everything that looks like it can be diagrammed. This will help you see where it wasn’t necessary or worth it. As you get better, start experimenting with jumping straight to the questions without diagramming or after you have diagrammed only a couple key inferences.

With practice (A LOT of practice), you will cut out a lot of unnecessary diagramming and turn into a faster, leaner LSAT logical reasoning machine.

As a final tip, let me add that you have don’t have to freak out if you start diagramming something and realize it’s not necessary. Nor is a big deal if you diagrammed a few more things than was needed to solve the problem. As you get better, diagramming goes fast. While it is good to skip it when it’s not needed, over-diagramming some of the time is not going to break you on the logical reasoning section.

Remember: practice a ton and use your instincts. Though we have called this ‘logical reasoning basics,’ fine tuning when to diagram is a fairly advanced strategy and may be one of the final things to really click only in your last weeks of study. Practice by doing plenty of full, timed logical reasoning sections.  Good luck!