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Weaken | Video lesson

Watch one way to approach a question that asks you to identify a choice that weakens an argument on the logical reasoning section of the LSAT.

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  • blobby green style avatar for user hiedomarleen
    This question was just way too time consuming...
    (8 votes)
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  • blobby green style avatar for user Ari S
    why cant we go with choice A' why cant we say its not the road closure that caused the increase - its the migration ( By introducing a new sufficient element - we weakening the support - road closure as the cause) (if the migration came from inside the valley the conclusion of doubling the population is weakened as mentioned. Now even if the migration came from outside the valley it still wont strengthen the argument because the argument supposes that the increase clearly came from road closures and we are showing that its just a correlation not a causation)
    (2 votes)
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    • blobby green style avatar for user Gavy G
      Although I initially though the same, re-watch the video and make note of the argument. Yes it would weaken the argument, but its not the strongest answer to weaken the argument - as the main answer we were looking for concerns weakening the correlation between the increase in the preserve population to the increase in the valley. If the valley population has stayed the same for the past 8 years, then it would weaken the author's argument (that due to the increase in the preserve population, the valley population will follow as such) as it shows that the bear population increase doesn't follow the same way.

      Hope I could help, and if I explained it incorrectly, I hope someone can explain it correctly!
      (4 votes)
  • boggle yellow style avatar for user Michael Dunlap
    When I read E, it says "has" and it seems like it is undermining the stimulus premise. Does anybody know how to not look at it this way on test day?
    (2 votes)
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  • blobby green style avatar for user jmcnutt147
    A bit late, but the answer isn't A because we can't assume that the migration had nothing to do with the roads being closed. If the migration was due to the road being closed, that would strengthen the argument. All the migration choices require this sort of assumption. By contrast, E directly contradicts the conclusion, thereby weakening the argument. Be careful not to make any assumptions when reading these choices!
    (2 votes)
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  • blobby green style avatar for user Balkrushna Vaghasia
    Any help from the experts would be very helpful here.

    At 9.18, Ma'am says that "even though bear population in the preserve doubled, the bear population in the valley remained the same. Therefore, this scenario shows that what worked for the preserve may not work for the valley."

    I have a doubt because what information given in the option E is about the last 8 years whereas the conclusion talks about future. Why the idea of closing did not work for the whole valley in the past? Its because roads were not closed in the whole valley and were closed only in the preserve.

    Therefore, in my opinion E can not be the correct answer.


    Rather I believe that option A is the correct answer. Why do I believe so? Let's see here.

    Author presents analogy in his or her argument. Roads were closed in the preserve for last 8 years and population of the bear got doubled. What is the analogy? If we close the road in the whole valley, the bear population in the whole valley will get doubled. So the author uses incidence of preserve as an evidence to make her claim.


    Now let's evaluate option A.

    Option A says that, in last 8 years, bear population in the preserve doubled because of migration. Do we know from where did those extra bear come? They may have come from the other parts of the valley or outside of the valley or the moon. Who knows? But question that from where these extra bear came doesn't matter because this option clear shows that the increase (doubled) in the bear population was not due to roads and was due to migration. Thereby, option A makes a big hole in the evidence presented by the argument.

    So, why option A is not the correct choice?

    Thank you.
    (1 vote)
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  • blobby green style avatar for user yqbao
    Hello, I have seen some comments. The reason why it does not choose A is that we want to make sure that the bear population in the preserve does not represent the Vally bear population. A is saying that more bears are going to the preserve, which means it is more representative of the Vally population. Therefore, it strengthen the conclusion not weakening it.
    (1 vote)
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  • old spice man green style avatar for user Ainsley
    I still don't understand why it isn't D? If population outside the preserve but within the valley decreased (while the population within the preserve doubled) doesn't that mean the same thing as E but with more certainty?
    (1 vote)
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Video transcript

- [Instructor] This question asks us, which one of the following, if true, most undermines the argument? So, we're looking at a weaken question. The answer will hurt the argument if we assume the answer to be true. The four wrong choices will either strengthen the argument or do nothing at all to the argument, if we assume them to be true. So, pause your video now if you'd like to try this question on your own, otherwise, let's move on to the explanation. Alright, we're going to read the stimulus together and for weaken questions, it helps to read actively for the conclusion and the support. That's because the connection between those two part is what we're going to be looking to weaken. So, the passage reads, the Kiffer Forest Preserve, in the northernmost part of the Abbimac Valley, is where most of the bears in the valley reside. During the eight years that the main road through the preserve has been closed, the preserve's bear population has nearly doubled. Thus, the valley's bear population will increase if the road is kept closed. Alright, there are a lot of pieces to pay attention to here because sometimes students rush through a question like this and they misunderstand the parameters that are given. First of all, what's the conclusion? Well, it's pretty safe for us to identify the last sentence as the conclusion. Since it starts with thus, it's a prediction and the rest of the passage looks exactly like it's giving information as support. So, our conclusion is that valley's bear population will increase if the road is kept closed. This is a conditional prediction. If we keep the road closed, the valley will have more bears. Alright, now, why did the arguer think this is true? The evidence gives us some context and relationships, so it's important to get the information straight. There's a preserve which is in a valley and most of the bears in the valley are in that preserve. For the last eight years, the road through the preserve has been closed and the preserve's bear population has almost doubled. There are a few places that could be difficult for us if we don't pay special attention to them and it's completely okay to draw a picture for ourselves on test day. So, let's say this is the Abbimac Valley and at the northernmost part, we have the Kiffer Forest Preserve. We're told that most of the bears in the valley reside in the preserve and over the last eight years, while the road was closed, the bear's population has almost doubled. Now, for weaken questions, it's usually the case that there are lots of different specific ways to weaken that argument, so a specific prediction isn't necessary or even recommended. What we can do to help ourselves is look for any gaps between the evidence and the conclusion. One thing that might stand out here is that we learn things about the preserve's bear population and the evidence, but the conclusion is actually all about what? The valley's bear population. Now, that's a gap. The arguer must be assuming that what happens in the preserve is representative of what happens in the valley itself. So, if we find a choice that attacks that assumption, we would have a weakener. The arguer is also assuming that it's not just a coincidence that the road was closed at the same time that the bear population doubled, so the answer could attack that assumption as well. So, to rephrase our task, we're looking for something that makes it less likely that the valley's bear population will increase if the road is kept closed, even though the preserve's bear population has nearly doubled while the road was closed over the last eight years. And we'll keep an eye out for any choice that shows that what happens in the preserve isn't representative of what happens in the valley or that there's some other reason that the bear population doubled besides the road being closed or something that the road being closed would affect. Now that we know what we're trying to accomplish, let's evaluate the choices. A, most of the increase in the preserve's bear population over the past eight years is due to migration. This could be tempting, but it doesn't actually hurt the argument. If we learned that there are more bears in the preserve because a bunch of bears migrated from other parts in the valley, then that would weaken the argument since bears just moved from one part of the valley to the other and didn't actually increase the valley's population. But we could also learn from this choice that there are more bears in the preserve because a bunch of bears migrated from outside of the valley, and then that wouldn't weaken the argument at all and it might even strengthen it, so we can eliminate this choice. It doesn't give us enough information. B, only some of the increase in the preserve's bear population over the past eight years is due to migration of bears from other parts of the Abbimac Valley. This choice could actually strengthen the argument. Just like we saw in choice A, there's a possibility here that a large part of the population increase is due to migration from outside of the valley or lots of the bears in preserves making baby bears because the road is closed. That would help the arguer's case that the valley's bear population will increase if the road is kept closed. C sounds really similar to B, only some of the increase in the preserve's bear population over the past eight years is due to migration of bears from outside the Abbimac Valley. Okay, this choice doesn't weaken the argument either because even if only some of the increase is due to bears migrating from outside the valley, it's still possible that the road being closed is what sparked that migration, and so if the road stays closed, it's completely possible that the valley's bear population will increase and that helps the argument. D, the bear population in areas of the Abbimac Valley outside the Kiffer Forest Preserve has decreased over the past eight years. Hmm, tempting, but this information by itself doesn't affect the argument. Let's say the bear population in the area outside the preserve decreased, but only by one bear. Well, if the preserve gained 100 bears in the same time, then this choice doesn't hurt the argument, so we are missing information in this choice about exactly how much the bear population in the valley decreased in comparison to how much the preserve population increased. We're getting there. Choice E, the bear population in the Abbimac Valley has remained about the same over the past eight years. This weakens the argument and not just because every other choice was wrong. This choice very subtly states the same thing we were looking for, which is that what happens with the bear population in the preserve isn't matched by what happens with the bear population in the valley. If that's a little confusing to you, let's go back to our drawing. Alright, let's see how adding choice E to the argument weakens the argument because that's essentially what you're doing with a weaken or strengthen question. You're adding this information to the argument and asking yourself, okay, what happened to the argument when I did that? First fact, most of the bears in the valley reside in the preserve, so let's make six bears in the preserve and five bears in the rest of the valley. There, six of the 11 bears, and that's most, are in the preserve. Two, we know the preserve's bear population has almost doubled. Alright, let's add five little bears to the preserve. So, here's five more little bears, which almost doubled the preserve's population, but wait, we also know from choice E, which we're testing, that the bear population has remained the same for the last eight years. So, for that to be true, at the same time that the preserve's bear population has almost doubled, we would need to get rid of about five of these valley bears. So, either these five valley bears left the valley or they're the ones who went to the preserve or maybe they went to bear heaven, either way, the argument is now weakened because we can't say that the valley's bear population will increase. Make sense? This is our answer because it shows that even though the preserve's bear population doubled, the valley's bear population stayed the same overall. So, to recap, for weaken questions, you're finding the choice that hurts the link between the evidence and the conclusion. It really helps to separate the evidence from the conclusion by seeing the evidence as information that we're given and then seeing the conclusion as an opinion that the arguer makes based on that information. So, in weaken questions, we wanna drive the two pieces farther apart. We wanna make it less likely for the conclusion to happen based on the evidence that was provided. It can also help to pretend that you're adding each choice to the argument and then seeing which way the argument moves in terms of quality. So, look for any gaps in the argument, like where the evidence is addressing one thing and then the conclusion addresses a different thing or sometimes you can also attack an argument by finding a possibility that the arguer has overlooked. So, stay really focused on structure and keep your eye on the task.