SA Q: how to know which premise to use, and which useless?

youbbyun

Hey all,

So for some SA Q that use logic and are formulaic, there are cases where there are 2 premises in the stimulus, and it turns out that you're only supposed to use one as the "bridge" or "link" to get to the conclusion. The other premise is thus USELESS. How do you know/decide which premise to use?

An example is PrepTest June 2007, Section 2, #23.

2 premises are stated in the stimulus. You then have to figure out the common sense assumption that one element in the conclusion links up to ONE premise, and then use that as the bridge to the conclusion. the other premise is thus useless/nonrelavent.

it's easy to say this now after knowing the correct answer choice, but when you're doing SA questions on the fly and you're presented with multiple premises/bridges/conditional statements, how do you know which one to use, and on the flip sides, which ones are useless?

Many thanks for the help.

olepueblo

Heller there,

I would be tempted to advise against using any hard and fast rule to identify which premise to use to link the conclusion. Rather, view the conclusion as your destination and think of the premises as your path(s) to get there.

P1: inc well being —> morally right
P2: red well being <—> morally wrong
C: leave well being unchanged —> morally right

How are we going to get to this unchanged business from premises that specify increasing and decreasing? Think of the contrapositives. Not increasing could mean decreasing but also mean leaving unchanged, same with not reducing. But if you find the contrapositive of premise 1: ~morally right —> ~inc well being, we would only be satisfying a necessary condition if things are left unchanged, which doesn’t tell us whether the action is morally right or wrong. However, if we do the same with premise 2, leaving well being unchanged tells us that something is not morallly wrong (not reduce well being <—> not morally wrong). Now we’re going places!

So the furthest we can go from the supplied premises when we’re trying to leave well being unchanged is concluding that something is not morally wrong. But this is not the same as being morally right. But, answer choice c makes it so. So, I quickly took both premises into account and decided one was taking me places and the other wasn’t. I’m not sure that that analysis could be avoided with a rule of thumb.

1luv
-Sam

goingfor99th

Use your answer choices to test them.

olepueblo

Are you saying to use answer choices to test which premise to use?

If so, I would recommend not doing that unless you’re desperate (which happens on the Lsat). Rather, get good at analyzing the passage before looking at the answer choices. The answer choices are designed to f u up... “It’s a trap!”

Your analytical skill will improve through rigorous br.

-Ackbar

goingfor99th

@swamlepow said:
Are you saying to use answer choices to test which premise to use?
-Ackbar

No, I don't think that's what I'm saying. I'm saying that you should read over the answer choices in an effort to identify which premise from the stimulus is used to setup that particular SA question. Not every SA stimulus allows you time to prephrase a single answer.

goingfor99th

On SA questions, in the stimuli you are given:
Premise: A -> B
and
Conclusion: A -> C

On SA questions, you are asked to find in the answer choices:
Premise: B -> C

Perfect Argument:
Premise 1: A -> B (given in stimulus)
Premise 2: B -> C (must find in answer choices)
Conclusion: A -> C (given in stimulus)

Of course, this is a generic example.

olepueblo

I see. But how would you know which one to use when multiple answer choices target multiple premises? They build the answer choices to lead you in the wrong direction. Wouldn’t you just be left at square one if it weren’t for your analysis of the stimulus?

olepueblo

I’m not sure that every sa allows for a perfect prephrase but I would think that someone with high level analysis could do a pretty decent job to get to at least a vague prephrase or thought of how the connection ought to be made without ever looking at an answer choice.

goingfor99th

@swamlepow said:
I see. But how would you know which one to use when multiple answer choices target multiple premises? They build the answer choices to lead you in the wrong direction. Wouldn’t you just be left at square one if it weren’t for your analysis of the stimulus?

I'm honestly perplexed by your opinion on this. You don't use answer choices to help find the correct answer? I've always done that. Not only do I find it a completely natural process, it is also massively efficient. This is not to say that I do not also do my best to fully process every stimuli prior to moving to the answer choices, though.

If your analytical ability is so well-developed to be able to crush every single LR stimuli without ever glancing at the ACs, how is it that ACs are so easily able to throw you off the scent/trick you?

goingfor99th

@swamlepow said:
I’m not sure that every sa allows for a perfect prephrase but I would think that someone with high level analysis could do a pretty decent job to get to at least a vague prephrase or thought of how the connection ought to be made without ever looking at an answer choice.

Of course. That's the first step. You should always digest the stimulus first, imo. On the more difficult questions, however, prephrases were rarely worth the effort for me.

goingfor99th

I think we may be talking past each other a bit.

youbbyun

Thanks guys for following up and the helpful advice!

keets993

To be honest, and this is not the answer you're looking for, but I'm not sure you can ever tell which premise is relevant and which is not until you look at the answer choices. There have been times I'm doing an SA question and I've spotted a gap and I've anticipated it as the most classic cookie cutter type of SA. But I glance down at the AC's and it's not there. At that point you can circle the question and move on or use the answer choices available to guide you. By that I mean, eliminate what you know is definetly not the SA.