“Unless” Statements in 2 Minutes

by Mary Richter Sep 26, 2013

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Lately, I’ve been getting asked a lot about notating “unless.” I figured that with the LSAT so close, it might be helpful to write up a quick-and-dirty how-to designed specifically for those of you who need to lock it in last minute.

The quickest way to learn how to diagram “unless” as a conditional is to translate it “if not.”

I can’t ride the ride unless I’m over 4 feet tall =

I can’t ride the ride [if not] over 4 feet tall =

Not over 4 ft –> Can’t ride ride

But wait! Didn’t “if not” appear in the middle of the sentence? Why does it leap to the beginning in our diagramming? Like with any “if” that appears in the middle of a sentence we are diagramming, we just pluck it up and place it at the beginning of our conditional. This is because the left side of the arrow is always the “if” side (the conditional side), regardless of how the original sentence is organized. So:

I will eat that banana if you pay me 10 dollars =

Pay me 10 dollars –> Eat that banana

Translating “unless” to “if not” fits right into this model. Try a few more, and I’ll put answers at the end of this post:

1. Don’t move unless I tell you to!

2. Ask unless I say otherwise.

3. Lean on me unless I’m not there.

Now, here’s a slight twist for plural conditionals, such as the one that appears on PrepTest 69, Section 4, Question 6. That question asks you to translate an unless statement but gives you two “unless” triggers. Like this:

She is going to return the blow dryer unless it starts working again or she can’t find her receipt.

If we apply the “if not” strategy, this sentence becomes:

She is going to return the blow dryer [if not] it starts working again or she can’t find her receipt.

So it seems we would diagram that:

If doesn’t start working OR can find receipt –> Will return

But what’s the problem with that? Think about it–does that actually reflect what we’ve been told? This sentence …

If doesn’t start working OR can find receipt –> Will return

… tells us that if either thing happens, that’s enough to guarantee she returns it. But that’s not true! If it doesn’t start working again, that’s not sufficient to know that she will return it, because she still needs to find her receipt. For this to make sense we have to change the OR to an AND:

If doesn’t start working AND can find receipt –> Will return

And the contrapositive would be:

Won’t return –> Does start working OR can’t find receipt

This means we have to add a second rule to our strategy for translating “unless” statements into conditional (if –> then) statements:

1. “Unless” becomes “if not.”

2. In the “unless” (“if not”) clause, “and” becomes “or” and “or” becomes “and.”

Answers to drill above

1. I don’t tell you to –> Don’t move [Contrapositive: Move –> I tell you to]
2. I don’t say otherwise –> Ask [Contrapositive: Don’t ask –> I said otherwise]
3. There –> Lean on me (Can be tricky, but “if not not there” just means “there.”)
[Contrapositive: Don’t lean on me –> Not there] ?

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Mary Richter is a Manhattan Prep instructor based in New York City. Mary has degrees from Yale Law School and Duke. She has over 10 years of experience teaching the LSAT after scoring in the 99th percentile on the test. She is always thrilled to see students reach beyond their target scores. At Yale, she co-directed the school’s Domestic Violence Clinic for two years. After graduating she became an associate at Boies, Schiller & Flexner LLP in New York City, where she was also the firm’s pro-bono coordinator. Her writing has appeared in the New York Times, The Atlantic, Slate, and more. Check out Mary’s upcoming LSAT classes here.