PT5 LR1 Q12 ... Necessary Assumption Question? Forum

[tehrocstar]

In Preptest LR1 Question 12, this question answers correctly with a necessary assumption. However, the prompt is: "The conclusion is properly drawn if which one of the following is assumed."

I've considered the fact that the answer could be necessary and sufficient. However, I feel strongly this isn't the case. For reference, Preptest 7 LR2 Question 23, has the same prompt, word for word. However, this question is clearly a sufficient assumption question.

Will someone please explain?

[suspicious android]

It looks to be both necessary and sufficient to me. Can you say more about why you don't think it is sufficient?

The question stem is definitely asking for a sufficient assumption, we agree on that.

[tehrocstar]

Thanks for replying.

I don't think the answer is sufficient for mainly two reasons:

1. The answer should be along the lines of "If abundance of securely identified craters... then lower rates of destructive geophysical processes." Specifically, the correct answer does not provide a link between the premises and conclusion when one is needed.

2. There are potentially other reasons why there could be an abundance of craters in geophysically stable regions. Perhaps, due to human involvement, there are less craters in geophysically not stable regions (I know crazy...).

With the answer, here's the argument:
Meteors falling evenly + an abundance of craters = lower rates of destructive geophysical processes

I'm not buying that those the answer and the premise guarantee lower rates of destructive geophysical processes.

[suspicious android]

1. The answer should be along the lines of "If abundance of securely identified craters... then lower rates of destructive geophysical processes." Specifically, the correct answer does not provide a link between the premises and conclusion when one is needed.

Yeah, I definitely see what you're getting at. The answers to these kinds of question often have that X --> Y format, where X is some element of the premises and Y is some element of the conclusion. But I'm not comfortable saying the answer choice should follow that format. It just usually does.

2. There are potentially other reasons why there could be an abundance of craters in geophysically stable regions. Perhaps, due to human involvement, there are less craters in geophysically not stable regions (I know crazy...).

Are there really other plausible causes other than geophysical processes? You suggest human actions of some sort but then immediately call that crazy, since your own knowledge of the real world suggests humans can't really be responsible for that. Alien intervention? Another logically possible, but not realistically plausible cause. God? No comment. But absent the actions of some intelligent agent, are we not left with "natural" geophysical processes?

I'm not buying that those the answer and the premise guarantee lower rates of destructive geophysical processes.

Long story short, I'd say that from time to time the LSAT requires us to supply our commonsense knowledge of the real world. More typically on questions that ask for things that are "strongly supported" rather than on sufficient assumption questions, but I think (and more importantly so did LSAC) no less validly in a situation like this. My rule of thumb has always been that if reasonably bright, college educated person would know a thing to be true, it's okay to add that in as an assumption of the argument.