Complete Question Explanation
Strengthen—CE. The correct answer choice is (D)
The scientific/medical subject matter of this stimulus is intended to distract you from the argument,
which otherwise is not too complicated. The author starts out by telling us about a recent study that
establishes a correlation between “continued deterioration of the nerve cells in the brains” of stroke
patients and the “highest levels of the protein glutamate in the blood” of those patients. To provide us
with some background information, the author explains that glutamate is a neurotransmitter and can
kill oxygen-starved cells. Based on this correlation, the author concludes that it is glutamate “leaking
from damaged or oxygen-starved cells” that is “a cause of long-term brain damage resulting from
This is a Strengthen question, and a readily apparent issue from the stimulus is the argument’s causal
inference from evidence of a correlation. However, the inclusion of the indefinite article “a” in the
conclusion, i.e., “a cause,” shifts our prephrase away from the standard correlation-to-causation
focus of many causal Strengthen and Weaken questions. While it is still flawed to conclude that the
correlation proves any causation at all, this conclusion is not as weak as a more definitively causal
conclusion indicating that the cause mentioned in the conclusion is definitively the only cause.
Instead, our prephrase will focus on the unsupported transition made in the argument from the
evidence provided in the first sentence to the conclusion: the addition of the origin of the glutamate
being leaked “from damaged or oxygen-starved nerve cells.” We know from the second sentence that
glutamate can leak from such cells, but there is no indication here that the glutamate found in the
patients’ blood came from “damaged or oxygen-starved cells.” The unsupported identification of the
source of the glutamate found in the patients’ blood gives us a superior prephrase that can help us
blast through these answer choices.
Answer choice (A): This answer choice is incorrect because we do not know whether the patients at
issue have any “damaged or oxygen-starved cells” in their bodies.
Answer choice (B): Here, the information has no effect on the conclusion, because we do not know
what is meant in this context by “abnormal,” and we do not know what would be the effect of these
abnormal levels on the brains of stroke victims.
Answer choice (C): Even if glutamate is the only neurotransmitter to leak from such cells, that
information does not strengthen the conclusion because we do not know if there are any “damaged or
oxygen-starved nerve cells” in these patients.
Answer choice (D): This is the correct answer choice because it fixes a flaw in the argument’s
conclusion, the identification of the source of the glutamate in the patients’ blood. This answer
choice states definitively that “damaged or oxygen-starved nerve cells” are the only source of
glutamate in the blood.
Answer choice (E): As with answer choices (A) and (C), this information does not strengthen the
conclusion because we do not know whether the patients have any such cells in their bodies.
#20 - In a recent study of stroke patients, those who
I picked C as my answer. Is C wrong because we do not know necessarily know that another leaked neurotransmitter would have any harmful effects whereas we know for sure that glutamate has harmful effects? And so C is correct because it eliminates the possibility of glutamate coming from anywhere else in the body and therefore strengthens the conclusion that glutamate leaking specifically from damaged or oxygen-starved nerve cells is a cause of damage from strokes?
That's basically right about C; other leaked neurotransmitters might have no effect at all, harmful or otherwise, for all we know. And D is correct because of what you said, largely. An "alternate cause" is eliminated, so to speak.
Hope this helps,
I thought C is wrong just because it doesn't have to be true it is the only one that leaks...
The conclusion is about causation, and C does not suggest there is causation.
I didn't think about others can have cause etc as previous poster did...
Does this mean my reasoning is insufficient?
You are analyzing this question as if it were a Must Be True question, but it is not - it's a Strengthen question. It makes no difference if a particular answer must be true - what matters is what impact the answer has if it is true. So, treat answer choice C as if it is true, and ask yourself whether than answer would strengthen the conclusion in the argument. As David explained, it does not.
Remember to focus always on what you are supposed to be doing to or with the stimulus, based on what the stem asked of you. Here, you are not being asked to measure the relative truth of the various answer choices, but only what their impact would be on the argument if they were all equally true.
Adam M. Tyson
PowerScore LSAT, GRE, ACT and SAT Instructor
Follow me on Twitter at https://twitter.com/LSATadam
Hi, I'm still unsure why C can be ruled out here. If there was another neurotransmitter that can leak from the bad cells, wouldn't that weaken the argument here? I don't understand why D is better. To me, D shows the only source for glutamate in the blood, but why do we care that this is the only source?
We know that Glutamate is a neurotransmitter, Freddy, and that if it leaks then it causes damage. We don't know that any other neurotransmitter that leaks causes damage, though. It could be that lots of neurotransmitters leak and do no harm, so saying that no others leak doesn't matter.
If we had an answer that said "no other harmful substances leak" from those damaged cells, that might help by eliminating other leaking substances as alternate causes. But since there is no reason to believe that other neurotransmitters are harmful, this answer has little to no impact.
D, on the other hand, is much, much stronger, in that it eliminates any other possible source for the one harmful substance that we know about. If D is true, it MUST be that the Glutamate leaked from those damaged cells, making leakage from damaged cells a more likely cause. It could not have come from an injection, or been in food ingested by the patient, or been simply created by the body's natural processes, maybe as a liver secretion, etc. That makes glutamate that leaked from damaged cells a much better suspect to blame for the damage.
Adam M. Tyson
PowerScore LSAT, GRE, ACT and SAT Instructor
Follow me on Twitter at https://twitter.com/LSATadam
I am troubled by the fact that no one, in any online forum or discussion of this question, addresses the fact that it says that glutamate CAN kill the cells. Not only that it only CAN but that there is an IF attached. The IF may not be significant because one can tack all kinds of ifs on statements that are universally true, i.e., My dog is a dalmation if it is Tuesday. Because my dog is and is always a dalmation so the if statement adds nothing. Though it can be useful for proving the CAN part of it if the IF is true. But in this case we don't know that glutamate DOES kill the nerve cells, only that it CAN. I CAN make breakfast for my neighbors and this CAN may include an "IF I am wearing a hat" (which of course is also true if I CAN make breakfast for all of them) but if someone observes my neighbors eating breakfast they would know nothing about my involvement from either the fact that they are eating breakfast or the fact that I am (assuming I am) wearing a hat. So if my neighbors were observed eating breakfast while I walked by wearing a hat, the statement "Thus, lsatstudentQ wearing a hat is a cause of breakfast being prepared and eaten by lsatstudentQ's neighbors" could possibly be true but would not be true for any logically-drawn reasons. Same for the conclusion that Glutamate CAN kill surrounding nerve cells being sufficient to conclude that glutamate DOES kill or IS killing or HAS killed brain cells. But the conclusion says that it IS a cause of long-term brain damage etc. That is an unjustified leap. Which is fine, as long as we realize it. This is a fascinating question in that it presents a series of logical errors and asks us to repair only one of them, leaving the conclusion still invalid. Many people would find it difficult to conceptualize this as STRENGTHENING when it leaves something that is not strong at all. But we are repairing a button on a garment that still can't be worn or used in any meaningful way. And calling that an improvement, simply because, I can only surmise, it is a valid step along the path of fully repairing the garment.
So the conclusion is too strong in any case. At best it should say something like "could possibly" or "may". And that is only one of the many weaknesses of this conclusion. The tricky thing about this question, I think, is that there is so much wrong with the conclusion that it would require a complete reconstruction of what leads up to it to make the drawing of that conclusion correct. But we aren't asked to make it correct. We are simply asked to "strengthen" it and in this case the strengthening is quite incremental and totally incomplete. So, at this point, realizing all of that, we can look at the choices and notice that only one of them works to improve at least something about the conclusion we are trying to improve. None of the others do in any way.
1) this doesn't matter. Our conclusion only speaks about glutamate, a specific type of glutamate (in terms of its source) at that. It doesn't matter whether other neurotransmitters do one thing or another. Some people might think that this weakens the conclusion but it doesn't even do that because it doesn't matter if other things damage the surrounding nerve cells since we are only asked to deal with the effects that Glutamate leaking from... has.
2)irrelevant. Way off target. It doesn't matter what else is in their blood. It may seem like this answer would suggest that something other than glutamate is doing this damage and that therefore it weakens the conclusion but it doesn't say anything about what these other substances do or don't do and in any case their effects or non-effects are outside the scope of the reasoning the conclusion is based on. (faulty reasoning but still..)
3)For people who aren't systematically running through an organized structure this might sound a lot like a plausible answer and I think people who are leaving some of this to feel would choose this option quite often. It just kind of sounds right. But that's it. You can't get any further than that. Such an approach works enough of the time that some people get a reasonable score more or less guessing like that, because it is a guess, but they find it difficult to get past a particular score range and often remain puzzled why. So let's look really clearly at what is wrong with this by considering when such a statement WOULD be relevant. If we knew that whatever caused this cell death/damage was a)definitely a neurotransmitter and b) could only have been something that had leaked from an oxygen-starved or DAMAGED cell, then this would be ALMOST conclusive in narrowing it down to being Glutamate that leaked from etc...
but we don't know that. In addition, to clarify my previous ALMOST - notice that they changed it to PHYSICALLY damaged? Physically damaged is a subset of damaged. The set of biological systems that can be "damaged" is larger than and includes the set of biological systems that are "physically damaged". So this answer would be a dud simply by that change in language alone. It would preclude all the different kinds of "damage" that aren't simply "physical" alone. And that is not such a little thing. That would be enough to make this answer incorrect and it is typical of the LSAT that they put little flubs in like that in situations like this. But in any case, even without that flub, the answer choice doesn't clarify or address any relevant logical or factual problem leading up to the conclusion being correct.
4)although we haven't established that this kind of damage is actually BEING caused by glutamate, (we only know that it CAN be caused by glutamate and we only know that this CAN is true under a particular condition of leaking etc.) and this is absolutely a critical failing in the logic leading up to the conclusion, were we to construe CAN be caused, in this case, to mean IS caused,(and we can't, but this would be yet another level of repair that would still have to be done) we'd still have to fix this part of the problem. The conclusion doesn't just say that the blanket thing known simply as "glutamate" causes this problem, it asserts, with great certainty, that it is specifically "glutamate leaking from damaged or ...." so this answer choice would establish that the only kind of glutamate that could be causing this problem (assuming we were provided with a fact that supported an assertion that glutamate actually DID cause this damage, not just possess the potential quality of CAN cause this kind of damage) would have to have come from this leakage and couldn't just be floating around from some other source.
What is tricky about this question and this answer is that the conclusion is still incorrect. And it is a strange use of language to say that we have "strengthened" something when that thing is still completely invalid. But if we were going to rebuild this entire question to correctly lead to that conclusion, at some point we would have to deal with the whole issue of whether glutamate can come into contact with brain cells from some other source than having leaked from damaged... etc. And since that is clearly a critical part of the conclusion we would have to deal with this at some point and so it does "strengthen" this still-erroneous logical progression to the still-erroneous conclusion if you choose to think of the word "strengthen" as including a situation like this where the result is still non-operational. I think that is a large part of what makes this a particularly tricky question.
5) it is irrelevant whether or not the brain cells that are leaking glutamate are being damaged themselves or not. As long as "surrounding nerve cells" are being damaged we have satisfied the condition that is given.
This is a relatively unique question. Not only does it attempt to trigger a standard reaction that would initially presume it is a correlation/causality question in a fairly deceptive way that breaks up as you continue through the systematically damaged logic, but it is followed by a series of statements that simply do not lead to the conclusion in a logical, defensible manner even with the repair offered by option D. But option D would inevitably be part of the repair/makeover that would allow the entire thing to follow logically. So it has to be chosen as no other option is offered that would of necessity be part of the necessary repair.
I know, this seems like an incredibly detailed answer. But in fact these things can be recognized in an instant, one just has to know they can exist and be there. I am including the detail to make sure that anyone that isn't following these particular elements of the world of this question can become aware of them in a clear and systematic fashion. Though it took a lot of words to articulate this I am recognizing it quite quickly and I think that once you break it down this far enough times you will begin to do it too if you hadn't up till now. But I think that simplifying this as far as so many others have is a complete disaster if your goal is to eventually get every single question right. And that is pretty much the only goal worth aiming for when one is preparing for a test like this because the logic of the entire test is within each question and there are few questions that aren't worth completely working out until they finally appear completely trivial and obvious because eventually they all start to seem that way. A lot of people are afraid to take the time dig fully into the workings of questions that seem to complicated to them but once they do it a few times they discover something kind of funny about all of this - it's much easier than it seems. But it's hard to go through the process sometimes of getting to that layer of really easy. So they simplify where they shouldn't and it remains difficult longer than it should. And I am quite certain that the issue of CAN vs. DOES kill surrounding brain cells is quite critical. If you don't spot that in this question and you treat it as if the two are the same you will find soon enough that you are dealing with a question where that kind of distinction is impossible to overlook and still get the question right.
Your evaluation of what is wrong with the argument seems correct to me. You also identified why answer choice (D) helped the argument.
You seem to have an issue with answer choice (D) in that it doesn't perfect the argument. But, after all, this is a Strengthen question, not a Justify question. If every Strengthen correct answer choice had to make the argument deductively valid, then the distinction between Strengthen and Justify would disappear. This question is not unique but in fact typical of Strengthen - usually (not rarely) the correct answer choice will not perfectly repair the argument. It will help it, but not enough to make it perfectly valid. This is typical and something to get used to.
You object that if an answer doesn't make the conclusion perfectly valid, how can it be the case that it strengthened at all? If we start with an invalid argument and end with an invalid argument, what progress has been made? I think the correct way to think about this is to imagine a list of problem with the argument, each with its own severity. Anything that takes a problem off that list, or reduces the severity of it, while not adding any additional problems, or increasing the severity of any other problem, will strictly make the argument better. Thus, that answer strengthens the argument. The same applies here.
Thank you for the intense analysis of this question. I hope my comments have helped you in turn!
So to clarify, given the statement in the stimulus, glutamate, which functions within nerve cells as a neurotransmitter, can kill surrounding nerve cells if it leaks from damaged or oxygen-starved nerve cells, we need to show that glutamate leaks from damaged or oxygen-starved nerve cells? I know this question involves causal reasoning but, for this statement, the sufficient is triggered?
The stimulus indicates the presence of glutamate in the blood, but there is no specific indication that this refers to the ones that are from damaged or oxygen-starved nerve cells, which would damage surrounding nerve cells, thus leading to long-term brain damage. Am I understanding this correctly? That is why Answer (D) eliminates the possible alternate uses for glutamate in the blood besides damaging surrounding nerve cells.
As for Answer (C), this can be ruled out because the conclusion states that glutamate leaking from damaged or oxygen-starved nerve cells is a cause of long-term brain damage resulting from strokes. The fact that glutamate is a cause, not the only cause means that there could be other neurotransmitters that leaks from oxygen starved or physically damaged nerve cells, which could possibly contribute to long-term damage.