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LR - Assumption Questions!!!

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anyone have any tips/tricks for necessary and sufficient assumption questions?

finding a hard time with those questions 

Edited by zanabsheikh

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This is probably basic advice, but for a lot of the SA questions that rely heavily on logic, you just have to identify the gap in the stimulus and then anticipate what fills in the gap, going into hunt mode when scanning the answer choices. Mapping out the logic can be useful, but if you can't do it mentally then write it down because they can get confusing. The same is with lots of NA questions. For NA questions, the negated correct answer will destroy the support that the premise(s) gives to the conclusion. Keep in mind that some NA questions also can be SA questions, but sometimes they will trick you by putting an SA answer in an NA question, so keep an eye out for those. I'd say that identifying the gap and trying to anticipate the correct answer choice is the most useful for me, though.

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I've previously listed some resources for tackling necessity and sufficiency, which you can find here (scroll down to the LR section)!

Here's a rundown in brief: to properly answer assumption questions you need to be able to identify what components of the argument are disconnected from one another. The disconnect typically takes one of two forms: one where premises don't quite link up but the conclusion doesn't introduce anything new, and the other where the premises are connected but some foreign concept is introduced in the conclusion.

In either case, it can be helpful to work backwards from the conclusion to identify the gap in reasoning. 

Lets take a simple example:

"Allan is a hockey player. All hockey players are bad at finance. All people bad at finance end up unhappy. Therefore, Allan does not smile"

The conclusion introduces a foreign concept: smiling. Smiling was never talked about in the premise set! Dead giveaway something is amiss here. Separate the conclusion and work from the side where you have information.


Conclusion: Allan ->                                                                                                                  -> Does not Smile

What info do we have? Well some stuff about Allan. So lets fill in the diagram a bit.

Premise 1: Allan -> plays hockey                                                                                            -> Does not Smile

Premise 2: Allan -> plays hockey -> bad at finance                                                             -> Does not Smile

Premise 3: Allan -> plays hockey -> bad at finance -> unhappy in the end 😞->            -> Does not Smile

Doing it this way clearly shows us where the gap in reasoning occurs. We have nothing to connect me being unhappy on my death bed to me not smiling! Hey, maybe I'm a little screwy and this could happen?!

Now before we get into what might be sufficient to justify the conclusion and what is absolutely necessary, lets review those two things. A sufficient assumption question is asking you to identify an answer choice that will make the argument valid 100% of the time. In other words, there is no world in this dimension or the next where the conclusion does not hold. A necessary assumption question is asking you to identify what has to be true in order for the conclusion to have any prospect of being true. In other words, what answer choice is such that without it the argument falls apart.  

Sufficiency in our toy example

In the case of our example, it's clear that an answer choice linking the two disconnected concepts in our diagram would be sufficient. It might read something like "when someone will be unhappy in the end they do not smile". This works and makes the conclusion totally valid if we assume the truth of the premise set. Job well done! But wait a second....does the answer choice have to play off that missing link? Why couldn't it be that "anyone bad at finance does not smile"?! After all, that makes the logic work 100% of the time too. And you would be right! 

Here's the thing though. LSAC will never jump a connected premise. So if they link all the premises and there is a disconnect between the premises and the conclusion, the answer choice will always play off that missing link. Answer choices that appear to work but jump a premise, are always screwed up and often in a very subtle way. You have to be on the lookout for these as they are very tempting traps. But the goods news is with the identification strategy employed above, you won't fall into that!

Necessity in our toy example

Lots of things have to be necessary! Actually, pretty much an infinite number of things. The good news is that like I mentioned above, LSAC will play off the missing link so we can focus our attention there. 

What has to be true otherwise the argument falls apart? Well, it HAS to be true that people unhappy in the end do not always smile. Because if they always smiled, Allan would be smiling! Okay...but it also HAS to be true that at least some people who are unhappy in the end do not smile. Still further, it has to be true that some of those that do not smile are unhappy in the end! We can play this game to infinity and beyond!

The key with necessary assumption questions isn't so much to identify the exact phrasing of what you are looking for. Because there can be nearly an infinite number of things that are necessary and the exact wording LSAC is going to go with is impossible to know in advance! Rather the important thing is to identify the concepts (where the disconnect occurs) that have to be related and the direction of that relationship. When testing answer choices, you go for the jugular. That is, you negate an answer choice and put it into the stimulus. If by negating an answer choice (finding the logical opposite) the relationship you identified no longer holds. That's a bingo!  

Hopefully that helps some. But the links provided in the other thread have a fair bit more explanation and I hope you check them out!

Edited by AllanRC

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An easy way to remember how to approach each question is:

(1) The answer to sufficient assumption question will make the conclusion of an otherwise faulty argument 100% true, 100% of the time. 

(2) The answer to a necessary assumption question, if negated, will destroy an otherwise valid argument 100% of the time.

Edited by LabouriousCorvid

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