LSAT Principle Questions, Part I

Update 2015: Practice makes perfect. You can find a list of principle questions + explanations for those questions here:


People often find LSAT principle questions confusing.

At first glance, this is strange. Principle questions are similar to regular question types. There are strengthen questions, parallel reasoning questions, etc. So why are LSAT principle questions hard?

It’s because principle questions are more abstract. The principles aren’t necessarily tied to a specific situation, and that’s hard to think about.

This is a two part blog post. In the second half, you’ll learn about LSAT principle questions types, and you’ll find a list of principle questions.

The first half covers something more basic, but even more important: what a principle is.

What Is A Principle?

In real life, we get away with using words imprecisely. This is fine. But on the LSAT (and in law), you need to be very precise with words. So you should know exactly what a “principle” is.

A good dictionary is surprisingly helpful for many LSAT terms, including this one. A principle is:

  1. A fundamental truth or proposition that serves as the foundation for a system of belief or behavior or for a chain of reasoning.
  2. A rule or belief governing one’s personal behavior.

If you accept a principle is true, it should change your thoughts or actions. And LSAT principle questions ask you to accept principles as true! So the right principle will change what you think of a situation.

You are not trying to figure out if the principles are true in real life. That is the wrong question to ask.

Instead, ask yourself “If this principle were true, would it change the situation?”

Narrow vs. Broad Principles

It’s important to know exactly when a principle applies to a situation. Consider these two principles. They sound similar, but one is much broader:

  • “New parents should eat a healthy diet.”
  • “Anyone who works should eat a healthy diet.”

The second principle is much broader.

If you accept that a principle is true, it will affect how you act or how you think about a situation.

Suppose you accepted the above principles, and that you work. You’re deciding whether to eat a chocolate bar. The principle does the job for you. Don’t eat it.

“I work, therefore I should eat a healthy diet. Therefore, I should not this chocolate bar.”

Take-away: Principles are often if-then (conditional) statements. You can use them to make formal logical deductions. In certain situations, a principle will force you to change your mind.

Bonus Question: What about someone who doesn’t work, and isn’t a parent. Should they eat a chocolate bar?

We don’t know. The principles don’t tell us anything about people who don’t work and aren’t parents. We have no idea what they should or should not do.

An Example

Let’s look at an example.

A robber comes to your house, and steals your computer. You lose all your pictures and music. Later, the robber turns himself in to police. He apologizes, says the robbery was a moment of weakness, and repents.

The robber is prepared to accept whatever punishment the law thinks appropriate. This is the robber’s third crime, and he will go to jail for life if found guilty.

Unfortunately, the computer was broken in the robbery, and you can’t get any data back.

The police come to you, and ask if you want to press charges. What do you say?

You might have already decided what to do. Or maybe you’re stuck and can’t decide between vengeance and pity. How do you decide, and what could force you to change your mind if you’ve already decided?

Applying Principles To The Example

There are certain principles that, if accepted, would force you to decide one way or the other. Suppose you believed that:

“Anyone who commits a crime must be punished, for the good of society”.

This principle tells you what to do. The robber committed a crime. Therefore, he must be punished. If you accept the principle, you have to believe this is true, even if you think the robber did a good thing by turning himself in.

Likewise, if you believe the following principle, the situation is clear:

“Anyone who repents of a crime deserves mercy and should not be punished.”

You can’t press charges if you truly believe this.

These are the kind of principles to look for. They express a firm belief that can change how you view a situation.

Some Principles Don’t Affect Anything

The wrong answers on an LSAT principle question typically describe a principle that has no effect, or a situation that isn’t affected by a principle. It’s very important to be able to identify when a  principle has no effect.

So let’s look at a few principles that won’t help us decide anything. See if you can figure out why they’re useless:

  • “All convicted criminals must be sent to jail.”
  • “You should not have mercy for a criminal who does not repent.”
  • “You should only punish a criminal if they cause irreparable damage.”
  • “You should only have mercy for a criminal if they repent.”

Did you figure out what was wrong with them? The first two apply to the wrong groups. The robber is not yet a convicted criminal. And since the robber did repent, the second principle doesn’t apply.

This is very important. A principle that doesn’t apply to the case at hand has no effect.

The final two principles are trickier. They tell us necessary conditions for punishing a criminal or having mercy. The first one says you can’t punish a criminal who didn’t cause permanent damage.

But our criminal did cause permanent damage. So this principle is useless. It tells us we could punish him, but not that we should or that we must.

The same analysis applies to the principle about mercy. If you find this confusing, it means you need to do more work on what sufficient and necessary conditions mean. I’ve written more about this in my Basic Logic section.

That’s it for discussion of what a principle is. Check out Part II for more on LSAT principle question types, and a list of principle questions from tests 29-38.

Then, take a look at Part III to find explanations for a few sample principle questions, and to see a list of all the principle questions from LSATs 29-38.

4 thoughts on “LSAT Principle Questions, Part I

  1. Thanks for this explanation. Relating Principle questions to necessary and sufficient conditions makes things much easier to understand.

  2. Pingback: LSAT Principle Questions, Part II (Question Types)

  3. Pingback: LSAT Principle Questions, Part III (Examples and Explanations)

  4. “You should only punish a criminal if they cause irreparable damage.”

    But our criminal did cause permanent damage. So this principle is useless. It tells us we could punish him, but not that we should or that we must.

    I’m very confused by this justification. I believe this would be diagrammed as: if they cause irreparable damage —-> then you should punish a criminal. “Only” modifies a necessary condition and since you’ve stated the criminal DID cause permanent damage, the Sufficient Indicator, then why would the Necessary condition not happen?

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