If you want to have a successful LSAT test day, you need to learn to diagram. There are lots of ways I could say the same thing: Only if you learn to diagram will you succeed on LSAT test day, for example. Or: no one who succeeds on LSAT test day doesn’t learn to diagram.
One of the reasons diagramming is so great is that it lets you get all these statements down to the same logical structure:
Succeed on LSAT test day → Learn to diagram
Conditional statements such as the above are all over the LSAT. Many Logical Reasoning question types are chock full of them. Grouping games, especially the In and Out variety, often have nothing but conditional statements as rules. And conditional rules pop up not at all infrequently in ordering games as well. Therefore, you’re in trouble if you can’t diagram conditionals accurately. If you’re taking the October LSAT and you don’t yet know how to diagram, time’s a-wasting. Start today.
Every conditional statement has two conditions: a sufficient condition and a necessary condition. Once you diagram it, it’ll look like this:
Sufficient → Necessary
The key to turning English language sentences into a diagram is identifying what’s sufficient and what’s necessary. To that end, there are certain keywords that can help.
“If”, “all”, “each”, “every”, and the like all indicate sufficient conditions. For example, this sentence: Athletes take every class offered by the communications department, can be diagrammed as:
Communications class → Athletes
“Only if” indicates a necessary condition. The more you practice, the more the words “only if” should begin to resemble an arrow to you. Why? Whatever’s immediately to the right of the words “only if” goes immediately to the right of the arrow. For example, take: Only if the guy at the door is half blind will that fake ID work. The words to the right of “only if” are “the guy at the door is half blind,” so the diagram is:
Fake ID works → Door guy half blind
“Only” also indicates a necessary condition, but isn’t quite as easy to deal with as “only if”. I could say that the only people who run 100-mile races are a little crazy. It would mean the same thing if I said that only people who are a little crazy run 100-mile races. Two sentences that mean the same thing should have the same diagram. In either case, the referent of “only” is being a little crazy. So this is the necessary condition, and the diagram is:
Run 100-mile race → A little crazy
The word “unless” can be translated to “if not”. The same goes for “until”, “without”, and “except”. So, if I say you won’t become a lawyer unless you pass the bar, you can translate this to: you won’t become a lawyer if not you pass the bar. Since that last sentence wasn’t grammatically correct, you can adjust it to: you won’t become a lawyer if you don’t pass the bar. “If” indicates a sufficient condition, so the diagram is:
NOT pass bar → NOT become lawyer
On occasion, you’ll get a conditional statement that doesn’t have any of these common indicator words. In this case, your job is to isolate something that’s either sufficient or necessary. For example: a revealing costume is mandatory to attend the Halloween party. In this case, the key word is “mandatory,” which is indicating something necessary. So you can start with:
____________ → Revealing costume
Then ask, what’s that necessary to? The costume is necessary if you want to attend the party, so the diagram is:
Attend Halloween party → Revealing costume
Unless you want to waste time getting LSAT questions wrong that you could easily get right, it’s critical that you master diagramming. It takes practice but you can do it.
Get to work and you’ll be writing diagrams like a pro before you know it.