LSAT Prep Concept: Sufficient & Necessary

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Alright, I think it’s a nice time to review some of our LSAT prep basics, just in case you’ve forgotten any of the small details. I know that as the days trickle down you’re probably using your study time to hone in on those complicated questions and passages, so you may be neglecting some of your LSAT prep staples. Plus, going over the basics always helps give a nice confidence boost! So, how about we try our hand at diagramming a few Sufficient & Necessary statements?

(1) You can enter the Orchard Gardens Inn only if you have an access code. 

Remember our trick with the “only if.” Just draw an arrow straight through the “only if.” And place each part of the sentence on the appropriate side of the arrow. So this sentence should look like:

You can enter the Orchard Gardens Inn ==> have an access code

So we can read it:

If you can enter the Orchard Garden Inn, then you have an access code.

OGI ==> AC

Contrapositive: If you do not have the access code, then you cannot enter the Orchard Garden Inn.

not AC ==> not OGI

(2) Only if you are physically fit, can you become an Olympic athlete.

If we place an arrow through the “only if,” then the sentence will look like this:

Become an Olympic athlete ==> physically fit

OA ==> PF

Contrapositive: If you are not physically fit, then you cannot become an Olympic athlete.

not PF ==> not OA

(3) No mammals are cold-blooded

We read this as, if it is a mammal, then it is not cold-blooded. Think about it like this, if we did it the other way around, i.e. "if it is not a mammal, then it is cold-blooded," it would not be a true statement. Because the animal we are speaking of could be a bird, an animal that is not a mammal but is still warm-blooded. So, we know for certain that if it is a mammal, then it is not cold-blooded. Therefore, we will diagram this like so:

M ==> not CB

Contrapositive: If it is cold-blooded then it is not a mammal.

CB ==> not M

Alright, remember, whenever your LSAT prep brain is fried, make sure to try as hard as you can to pick up a literary magazine or newspaper or click open a political blog and read! I promise you’ll be surprised to see how often you’ll find Sufficient & Necessary statements and, more entertainingly, how often you’ll see writers make incorrect conclusions or assumptions. I know that doesn’t sound that entertaining, but, you gotta’ take what you can get in this Logical Reasoning world of ours!

Happy Studying!

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Updated on Aug 18, 2016