LSAT PrepTest 44 Section 2 Question 5 Explanation | Logical Reasoning

I didn't write the following blog post. It was already on the blog when I took over the URL. The following blog post may contain mistakes. -Steve

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This Logical Reasoning question is from the October 2004 LSAT.

Let's make a chain, or diagram of how the argument's logic works, to better understand it:

Adult musicians have bigger corpus callosa (CC's) --> adults who trained at 7 have even bigger CC's --> Music, especially if begun early, expands the CC

Do you see the jump here, the place where the logic needs an extra assumption in order to make sense? It's just before the final statement, the conclusion, and it's basically a matter of equating correlation and causation (of having bigger CC's). Adult musicians end up with bigger CC's than adult non-musicians, and the argument says this is because of their musical training earlier in life.

Let's pre-phrase an answer here so we don't have to plod through the wrong answers and can more quickly find the right choice. For it to be true that adult musicians have bigger CC's because of previous musical training, we would need to assume they didn't tend to have bigger CC's than non-musicians beforehand. If that pre-phrase didn't occur to you, no problem, you can still go through each answer choice, which we will do now.

A) Correct.

B) This assumption isn't needed because it's beyond the question's scope. Even if musical training later in life did affect CC size, it could still be true that previous musical training increased the size of the CC's of musicians so much that they still tend to be bigger than those who only took up music later in life.

C) Tricky, but not a needed assumption because it's beyond the question's scope. It isn't comparing musicians to musicians, but rather musicians to non-musicians, so whether a few musicians already had larger CC's than other musicians is irrelevant.

D) Not a necessary assumption because, again, it's beyond the scope of the argument. It isn't talking about every musician having a bigger CC than all non-musicians, just that the former group tends to have larger CC's.

E) Once again, not a needed assumption since it falls beyond the argument's scope. It isn't saying that adult non-musicians never enhanced their CC size in any way, but only that the ultimately ended up with smaller CC's than musicians. It could be that non-musicians enhanced their CC size a lot in various non-musical ways, but still not as much as musicians enhanced their CC size with musical training.

Remember:

1) Write down a few words that make a chain of the argument's logic, so you can see how it progresses and, in assumption questions, find the jump in it, the place where an additional assumption is needed for the logic to make sense.

2) Pay very close attention to the question's scope, what it's saying and what it isn't saying. If the claim in the answer choice is beyond the question's scope (if it's something the question wasn't talking about), it cannot be an assumption the argument needs. As you can see on this question and many others, it can eliminate a great deal of answer choices.

3) Try to pre-phrase an answer when possible, but if you cannot think of anything, don't spend too much time doing this. Just head on to the answer choices.