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General questions relating to the LSAT Logic Games.
 BenSven
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#76364
I'm going through the 2020 bible, and there's a section on page 157 about "Justify Questions." I.e. questions that take the form "X must be true if which of the following is true."

While the book offers some helpful tips, I think the obvious best strategy is missing: Simply contrapose the whole thing to get a more-normal question format:

If x is false, which of the following must be false. You can do this because y->x is equivalent to -x->-y. So rather than searching for which y implies x, you can simply suppose that x is false and see which -y follows necessarily.
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 Dave Killoran
PowerScore Staff
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#76369
BenSven wrote:I'm going through the 2020 bible, and there's a section on page 157 about "Justify Questions." I.e. questions that take the form "X must be true if which of the following is true."

While the book offers some helpful tips, I think the obvious best strategy is missing: Simply contrapose the whole thing to get a more-normal question format:

If x is false, which of the following must be false. You can do this because y->x is equivalent to -x->-y. So rather than searching for which y implies x, you can simply suppose that x is false and see which -y follows necessarily.
Hi Ben,

Thanks for the message! I'm a big fan of the contrapositive, and have considered this approach previously but chose not to include it in the book. But before talking about that, let me say this: if you find it helpful, by all means continue using it! LSAT prep is about what works for you, and whenever someone says they do something differently or have altered what we recommend and it works for them, I tell them to keep doing it :-D

For anyone wondering what this discussion is about, let me recap it. Any Justify question works along the following lines:

  • AnswerTrue/Correct :arrow: Conclusion/OutcomeTrue
Essentially, if you add a piece to what you already have, if it is correct that should then force the desired result. This is true in both LG and LR, and means the correct answer gives us the conclusion, or, in LG, whatever result they ask for.

Applying the contrapositive to the above relationship and honing in just on LG, we get:

  • OutcomeTrue :arrow: AnswerCorrect
This is the exact same idea as the prior diagram, just in contrapositive form (and I say it's the same because a statement and its contrapositive are different expressions of the same relationship). Let's apply how that would work to a typical LG Justify question.

For example, I'll use a question stem that is as simple as possible and one that represents a task they often ask you to perform, such as the one from June 2017, question #11: "The order in which the musicians perform is completely determined if which one of the following is true?"

As given, that relationship appears as:

  • AnswerCorrect :arrow: Order Completely Determined
In other words, which answer can you add to what we already have that will force everything to fall into place.

Now, the contrapositive:

  • Order Completely Determined :arrow: AnswerCorrect
In other words, if the order isn't determined, which of these is not true?

In working with students, looking at it from this angle didn't help them (and again, that's a generalized statement, as I said above, if it helps you by all means do it—you seem to have a high level grasp of how this works). It was difficult for them to consider the question in the context of the order not being determined because that was the natural state of the game, and then also to look at the answers in the negative was confusing. For most people, it seemed to make it more complicated, not easier. This was especially so because the majority of Justify questions focus on having the student completely determine the placement of all variables.

Anyway, it's a cool suggestion and I wanted to take a moment to explain that we had looked at previously and decided against recommending it as a general strategy (although, there's a similar relationship on the necessary assumption side, and we use the contrapositive there in the Assumption Negation Technique). It's a great sign for you though that you grasp the material on this level. I expect you are scoring pretty well :-D
 BenSven
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#76972
Thank you so much for replying!

I agree that the contrapositive method isn't helpful in all situations. But it's definitly helped me on some questions.

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