Sufficient & Necessary Practice

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So we’re at a little under a month away from the February 2015 LSAT Test. I thought we could get your LSAT prep into gear by going over some Sufficient & Necessary statements. It’s always important to keep your Sufficient & Necessary skills sharp, as they are needed on your Logical Reasoning sections and your Logic Games section.

Here are few examples we will go over together:

(1) The only time Naz sees stars in the sky is when she is staying with her cousin in Northern California.

Remember that “the only” introduces a sufficient condition, as opposed to “only,” which introduces a necessary condition. We can rephrase the statement: If Naz sees stars, then she is staying with her cousin in Northern California.

P: NSS ==> SwCNC

Not SwCNC ==> not NSS

(2) Evan can navigate using the stars only when he has taken an Astronomy class.

Here is a good example of “only” as opposed to “the only.” “Only” introduces the necessary condition. Meaning that Evan could have taken an Astronomy class and still not be able to navigate using the stars. However, if he can navigate using the stars, then he has taken an Astronomy class.


Not TAC ==> not ENUS

(3) Unless Sheva uses a telescope, she will not be able to see the Milky Way. 

The part of the sentence that does not include the “unless” is the sufficient condition. You must negate the sufficient condition and have it lead to the necessary condition—the part following the “unless.” So we can rephrase: If

Sheva is able to see the Milky Way, then she uses a telescope.

P: ASMW ==> UT

Not UT ==> not ASMW

Alright, I hope this stellar-themed blog drill was helpful in your continuing LSAT prep. Keep working on your rules and practice, practice, practice!

Happy Studying!

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Updated on Aug 18, 2016