Why and How LSAT Conditional Logic Wrecks Test-Takers


Manhattan Prep LSAT Blog - Why and How LSAT Conditional Logic Wrecks Test-Takers by Chris Gentry

This post is inspired by some recent in-class interactions with students, with an inspirational assist from Ally Bell’s post “Conditional Logic Doppelgangers.” I hope you enjoy!

At its most fundamental, LSAT Conditional Logic should be easy. Every Conditional Logic statement is an “If…then…” statement. If you drive a car, you must have a driver’s license. DC → DL. Done. Right?

When the situation for LSAT Conditional Logic is something common to everyday experience, most students diagram it correctly (after some time studying—you have to know that the relationship is “sufficient → necessary”). For example, I have rarely seen anyone struggle to diagram the statement “all dogs are mammals.”

D → M.

“If that thing is a dog, then it is also a mammal.” (Thanks, Aristotle!) Students do not diagram the dog to mammal relationship as:

M → D.

That’s not a sentence that confuses students.

But let’s consider what happens when you start to add negatives to a sentence. For example, “no cats are dogs.” How would you diagram that?

I’ve seen many, many students just do a literal-order translation:

~C → D.

I mean, that’s what was said, right? No cat arrow dog?

And this leads us to our first suggestion on how to study LSAT Conditional Logic.

After you’ve built your arrow diagram, rephrase the arrow diagram into an “if…then…” statement. Consider the statement you’ve made.

In this example, the “if…then…” translation of ~C → D is “if that is not a cat, then it must be a dog.”

Huh? Anything that’s not a cat is a dog? What about hamsters? Goldfish?

So let’s reconsider. How would we translate “no cats are dogs” into a sensible “if…then…”?

If it’s a cat, then it’s not a dog.

That sentence is now the literal-order arrow diagram.

C → ~D

So, first rule for studying LSAT Conditional Logic: review your work by breaking down each diagram into an “if…then…” format, and examine whether that sentence ‘works.’

But what if we’re dealing with a sentence that has no real-life, concrete visualization? I’ll offer two examples, both from actual LSAT problems.

The first is from a Logical Reasoning problem: “There can be no individual freedom without the rule of law.” I…have absolutely no idea what version of this is intended. If no freedom, then no rule of law? If freedom, then rule of law? What is this even saying????

Or, from a much older game: “V cannot be prescribed unless both H and M are prescribed.” That could not be more confusing and abstract!!!

So how do we tackle these? How do we prepare ourselves for them?

And this brings me to suggestion #2:

Have a real-life scenario you can substitute into weird, abstract LSAT Conditional Logic statements.

Mine is international air travel. To get on a plane, you need ID (we’ll say passport) and a ticket.

Does this mean that “if you have a passport, you’re on a plane”? No; I have a passport. It’s sitting upstairs in my condo right now. But I’m not on a plane. I’m in a conference room writing this blog post before my Monday deadline!

But…if you see me on an international flight…you know I have a passport.

So we can diagram:

plane → passport

Or, if we need a combo conditional, use passport and ticket.

plane → passport and ticket

So let’s see how this plays out in LSAT land!

“There can be no individual freedom without the rule of law.” Let’s take that sentence, carve out the content, and keep the shell. “There can be no ___________ without __________.”

Let’s put in planes and passports. Adapt the phrasing to make the sentence gel, so we’ll talk about “getting on a plane” and “having a passport.”

Version 1: “There can be no [having a passport] without [getting on a plane].” Really? In order to have a passport, you have to be currently boarding a plane??? That’s not right. I have a passport; that doesn’t mean I’m in the boarding line for a 12:45 p.m. flight to Madrid (as much as I may wish!).

Version 2: “There can be no [getting on a plane] without [having a passport].” Sounds awkward, but it does make sense. You can’t get on a plane without a passport.

And now we have our diagram: substitute “individual freedom” for “getting on a plane” and substitute “rule of law” for “having a passport.” So instead of:

plane → passport,

we diagram

IF → RL.

Let’s take the Logic Games example.

V cannot be prescribed unless both H and M are prescribed.

Let’s carve out the content, and adjust the phrasing a little bit…

“______ cannot happen unless both _____ and _____ are true.”

It’s not perfect, but it should get the job done.

“[Getting on a plane] cannot happen unless both [have a ticket] and [have a passport] are true.”

Substitute “V” for “getting on plane,” and “H and M” for “have a ticket and have a passport,” and we have our diagram!

V → H and M.


If this feels like a lot…well, it is. Sorry, but this test isn’t easy! So what does this mean? Study LSAT Conditional Logic early!! Study it often!! Take the time to truly understand where the diagrams come from, and don’t be satisfied with merely knowing code words like “only” or “unless.”

Good luck! 📝

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Chris Gentry is a Manhattan Prep LSAT, GMAT, and GRE instructor who lives in Atlanta, Georgia. Chris received his Bachelor of Science in chemical engineering from Clemson and JD from Emory University School of Law before realizing that he genuinely enjoys the challenge of standardized tests, and his true passion is teaching. Chris’ dual-pronged approach to understanding each test question has helped countless of his students to achieve their goal scores. What are you waiting for? Check out Chris’ upcoming LSAT courses here.

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