Politician:  Unless our nation redistributes wealth, we will be unable to alleviate economic injustice and our curren...

shunhe May 30, 2020

Hi @bcross,

Thanks for the question! It seems like you got a bit lucky in getting to the answer choice here, because your diagram isn’t completely correct. Your second conditional, IEI —> V, is correct (as it is quite a simple one to draw out). The first conditional, however, is very close, but not quite correct, and so let’s go through it to prevent any future mistakes.

Let’s take a look at the sentence you were diagramming: “Unless our nation redistributes wealth we will be unable to alleviate economic injustice and our current system will lead inevitably to intolerable economic inequities.” Remember that we can diagram “X unless Y” as ~Y —> X, or its contrapositive (which is logically equivalent), ~X —> Y. I’m used to diagramming it ~Y —> X, so that’s what I’ll do here, but I’ll take the contrapositive to show you your error. So here, we get

~RW —> ~AEI & IEI

Now we can take the contrapositive of this statement, which means we switch the sides and negate them. When we negate (X&Y), however, we have to follow something called De Morgan’s Laws, which means that we negate both the terms, and we change the & to a v (or). Similarly, we negate (X v Y) by changing the v to an & and negating both the inside terms. So the negation of (X&Y) is ~X v ~Y, and the negation of (X v Y) is ~X & ~Y.

So now, when we negate this, we get

AEI v ~IEI —> RW

Which is almost what you have, but an “or” instead of an “and,” and this makes a difference.

The explanation also diagrams it in another valid way. This question, just like all the questions assigned in the LSATMax course, now have detailed forward facing explanations that you can access when you “Review” your session. You will find unrivaled explanations written by our 99th-percentile instructors that include: (1) Argument or Facts, (2) Valid or Flawed, (3) Question Type, (4) Stimulus Summary, (5) Answer Anticipation, (6) Correct & Incorrect Answer Choice Explanations and (7) Key Takeaways. To ensure the optimal prep experience, please make sure you are taking advantage of these existing explanations before seeking further clarification on the message boards. 

Hope this helps! Feel free to ask any other questions that you might have.

bcross June 1, 2020

That did help, thank you! Just to clarify, my error wasn't using &/or when diagramming, but it was where I put them when setting up and taking the contrapositive, correct?

bcross June 1, 2020

Actually, I'm still not clear...with the unless rule, N is what follows unless and you negate the other part and make it S, right? So, wouldn't that be

AEI & not IEI --> RW

Motunrayo-Bamgbose-Martins June 9, 2020

Brittany, I did the exact thing you did- AEI $ not IEI ---> RW. I think this is right though? I think the issue surrounds how we interpret "unable to alleviate(get rid of)"- theres a lot of negatives when including the rules, which is confusing. But, I had what you had and am just as confused with the explanation.

Brett-Lindsay July 7, 2020

That is really confusing - depending on how we read the "unless" compound statement, we will get a different and/or statement:

If I do it the way it's taught, I get the same answer as @bcross:
(Make the "unless" clause the necessary clause and negate the other clause)
AEI & not IEI --> RDW
(not RDW --> not AEI or IEI)

If I approach it from the other perspective (by treating "unless" as an "if not"), I get the same as @shunhe:

not RDW --> not AEI & IEI
(AEI or not IEI --> RDW)

I know for this particular question, it didn't matter, but it might matter in a future question...