LSAT principle questions can seem confusing, but they’re really just other question types in disguise. For example, often we’re asked to use a principle to strengthen or weaken an argument.
These questions are just like normal strengthen or weaken questions, with one twist: the answers are phrased as abstract principles.
What Question To Ask Yourself About Each Answer
The right answer should force you to change your mind about the argument’s conclusion.
Let’s say I make the following argument:
“Even though there are useful ways we could spend tax money, we should cut taxes to boost economic growth.”
You may not agree with that argument, but you can see there’s at least a potential case to be made. If you do agree with it, you can surely see that it is not perfect.
Here’s a wrong answer:
“Economic growth is a good thing.”
It sounds a little tempting. The conclusion said that we should aim for growth, and this says growth is good.
But…would this principle force anyone to change their mind. Some people might think that we could achieve even more good by spending the tax money.
Further, it’s a very obvious principle. Practically everybody agrees that economic growth it good. That makes it a warranted assumption, something that we could assume anyone because no one would disagree with it.
Take Each Statement At It’s Weakest
Most people look at the answers to an LSAT question, and try to see whether it’s possible they’ll be useful. That’s the wrong approach. You should ask yourself whether it’s possible that the answer wouldn’t be useful.
The wrong answer above said that economic growth is good. But how good? We don’t know. Maybe economic growth is the best thing in the world. Or maybe it’s good, but not very good. Maybe it ranks a little higher than “steamed peas” on the scale of goodness.
So, properly speaking, the question to ask yourself is:
“If everyone agreed that economic growth was slightly good, would that convince them that we definitely should cut taxes to boost economic growth?”
“No”, is the answer to that question. There’s still room for disagreement.
What a Right Answer Looks Like
Take this statement:
“If some action will boost economic growth, then the government should take that action.”
Now ask yourself:
“If someone accepted that statement is true, would they have to agree that we should cut taxes to support economic growth?”
Yes, they would. The correct answer on a “principle: strengthen/weaken” question will force you to change your mind, if you accept that the principle is true.
Some students think that this kind of answer is “too strong”. I have no idea what that means. A strong answer choice does more than it needs to, but that’s fine, as long as the answer does help the argument. If you’re supporting an argument, you can never be “too strong”.
Update 2015: I’ve now written thousands of free explanations at LSAT Hacks, including explanations for principle strengthen questions: http://lsathacks.com/explanations/