Strengthening Questions

shegotit

So I am watching the Webinar on Weakening and Strengthening questions and I have a questions about the first question. The first question is a strengthening question and I have typed the stimulus and answer choices below.

Stimulus: Several years ago, as a measure to reduce the population of gypsy moths, which depended on oak leaves for food, entomologists introduced into many oak forests a species of fungus that is poisonous to gypsy moth caterpillars. Since then, the population of both caterpillars and adult moths has significantly declined in those areas. Entomologists have concluded that the decline is attributable to the presence of poisonous fungus.

A. A strain of gypsy moths whose caterpillars are unaffected by the fungus has increased its share of the total gypsy population.
B. The fungus that was introduced to control the gypsy moth population is poisonous to few insect species other than the gypsy moth.
C. An increase in numbers of both gypsy moth caterpillars and gypsy moth adults followed a drop in the number of some of the species that prey on the moths.
D. In the past several years, air pollution and acid rain have been responsible for substantial decline in oak tree populations
E. The current decline in gypsy moth population in forests where the fungus was introduced is no greater than a decline that occurred concurrently in other forests. (I thought that this was the answer.)

Questions

I know that with strengthening questions you are looking for the answer choice that strengthens the argument and blocks the alternative. I am a little confused on what exactly does it mean to block the alternative. After looking at the explanation of the webinar video for this question it seems as if blocking the alternative is an answer choice that provides another alternative. Is that correct? I believe that the whole concept of "blocking the alternative" is going over my head and I would like further clarification on this strategy. In addition, can someone explain how A strengthens the argument....A does not seem like it supports thew conclusion if the conclusion is saying that the fungus contributes to the decline of moths and A is talking about that the population increased.

CantStopWontStop

I have for notes of strengthen: add info so premises are more relevant to the conclusion.

So in this case the premise is that poison that affects gypsy moths was introduced, and the conclusion is that the decline of the gypsy moths was caused by the introduction of the poison.

What is added to Strengthen this argument is evidence of this causal relationship. It is also giving support that the decline was not due to some other factor (weather, lack of food, etc), and therefore it also "blocks."

Answer A supports the idea that the poison caused the decline, since there was a significant decline in the number of gypsy moths. And this should have been across the board. But because the strain of gypsy moths who were unaffected by the poison didn't go down proportionally, it seems like the poison did cause the gypsy moth decline. Because if it hadn't, this gypsy moth that was unaffected by the poison would have gone down too and not have increased it's proportion.

It's not airtight though, but it does strengthen it, even if it is by a tiny amount. The right answer strengthens it even a little, while the other 4 do not strengthen it at all.

E) Your answer, would actually weaken it. If it went down, similar to other forests then it was not the poison that caused it's decline.

I hope this helps. And anyone else, let me know if this is missing something

LSATisJustLikeDarkSouls

@shegotit said:
I know that with strengthening questions you are looking for the answer choice that strengthens the argument and blocks the alternative. I am a little confused on what exactly does it mean to block the alternative. After looking at the explanation of the webinar video for this question it seems as if blocking the alternative is an answer choice that provides another alternative. Is that correct? I believe that the whole concept of "blocking the alternative" is going over my head and I would like further clarification on this strategy. In addition, can someone explain how A strengthens the argument....A does not seem like it supports thew conclusion if the conclusion is saying that the fungus contributes to the decline of moths and A is talking about that the population increased.

In strengtheners the answer should strengthen the argument or at least block an alternative. Sometimes the correct AC for strengthening doesn't seem like it directly strengthens the stimulus, but it does by way of blocking an alternative.

A is the correct answer because it says "this other group of moths have an immunity to the fungus and they're all doing fine," which supports the conclusion of "the fungus is the reason for the reduction in moths without the immunity (the moths from the stimulus)."

E actually weakens the argument by saying: "in this other forest, where there is no fungus, moths are dying at the same rate as in the forest where the fungus actually is." Which weakens the whole "the fungus is the cause" thing.

Logic Gainz

You misread answer choice A. The population of a particular type of caterpillar hasn't increased, it's share has - i.e. its percentage of the population. Now ask yourself, what's the one thing that differentiates this resilient caterpillar and the one that saw a population decline? The key difference is that the former is resistant to the poison, whereas the latter clearly isn't. If you restate the conclusion in your head, the poison killed off the moths, then this helps support that notion.

E is almost like a control group disproving a hypothesis. The hypothesis is that the poison killed off the moths, but if the control group - i.e. the group that didn't receive the poison - also saw a population decline, then there is probably something else causing the decline across both groups, not the poison.

shegotit

@July2018Taker said:
I have for notes of strengthen: add info so premises are more relevant to the conclusion.

So in this case the premise is that poison that affects gypsy moths was introduced, and the conclusion is that the decline of the gypsy moths was caused by the introduction of the poison.

What is added to Strengthen this argument is evidence of this causal relationship. It is also giving support that the decline was not due to some other factor (weather, lack of food, etc), and therefore it also "blocks."

Answer A supports the idea that the poison caused the decline, since there was a significant decline in the number of gypsy moths. And this should have been across the board. But because the strain of gypsy moths who were unaffected by the poison didn't go down proportionally, it seems like the poison did cause the gypsy moth decline. Because if it hadn't, this gypsy moth that was unaffected by the poison would have gone down too and not have increased it's proportion.

It's not airtight though, but it does strengthen it, even if it is by a tiny amount. The right answer strengthens it even a little, while the other 4 do not strengthen it at all.

E) Your answer, would actually weaken it. If it went down, similar to other forests then it was not the poison that caused it's decline.

I hope this helps. And anyone else, let me know if this is missing something

Thank you for clarifying how E actually weakens the argument because that makes sense but the explanation still throws me off. How is answer A still supporting the fact that poison caused the decline if the moths were immune to it?

shegotit

@LSATisJustLikeDarkSouls said:

@shegotit said:
I know that with strengthening questions you are looking for the answer choice that strengthens the argument and blocks the alternative. I am a little confused on what exactly does it mean to block the alternative. After looking at the explanation of the webinar video for this question it seems as if blocking the alternative is an answer choice that provides another alternative. Is that correct? I believe that the whole concept of "blocking the alternative" is going over my head and I would like further clarification on this strategy. In addition, can someone explain how A strengthens the argument....A does not seem like it supports thew conclusion if the conclusion is saying that the fungus contributes to the decline of moths and A is talking about that the population increased.

In strengtheners the answer should strengthen the argument or at least block an alternative. Sometimes the correct AC for strengthening doesn't seem like it directly strengthens the stimulus, but it does by way of blocking an alternative.

A is the correct answer because it says "this other group of moths have an immunity to the fungus and they're all doing fine," which supports the conclusion of "the fungus is the reason for the reduction in moths without the immunity (the moths from the stimulus)."

E actually weakens the argument by saying: "in this other forest, where there is no fungus, moths are dying at the same rate as in the forest where the fungus actually is." Which weakens the whole "the fungus is the cause" thing.

Can you elaborate on what you mean by blocking the alternative? Should you create an alternative after discovering what the premise and conclusion is. I am not exactly sure what blocking the alternative means, it throws me off?

shegotit

@"Logic Gainz" said:
You misread answer choice A. The population of a particular type of caterpillar hasn't increased, it's share has - i.e. its percentage of the population. Now ask yourself, what's the one thing that differentiates this resilient caterpillar and the one that saw a population decline? The key difference is that the former is resistant to the poison, whereas the latter clearly isn't. If you restate the conclusion in your head, the poison killed off the moths, then this helps support that notion.

E is almost like a control group disproving a hypothesis. The hypothesis is that the poison killed off the moths, but if the control group - i.e. the group that didn't receive the poison - also saw a population decline, then there is probably something else causing the decline across both groups, not the poison.

I was with you till you said the last sentence of the explanation for answer choice A. I am not sure if I am having difficulty understanding the answer choices or if they are going over my head. If one was resistant to the poison then how is that strengthening the argument. Is this answer correct because its basically proving that the fungus was affecting the moths since one strain was unaffected? I think I am starting to see a little bit why it would be correct.

Logic Gainz

Lets say we have a forest of 100 moths. 50 of them were resistant to poison and 50 of them weren't. We then nuke this forest with the poison and come back a week later to find that the total population of 100 moths is now 70. The argument's conclusion is saying it's because of the poison, but we can't quite blame the poison yet.

On further analysis, we see that all 30 moths that died lacked resistance to the poison we just sprayed, while the other poison resistant moths still had 50 moths flying around still living. The resistant moths still flying around didn't see an increase in population, but they did increase their share of the total population from 50/100 to 50/70. Now we can strongly say that the poison is the probable culprit. This isn't for certain, but the argument that the poison is the thing that killed off the moths is strengthened. That's essentially what A says.

LSATisJustLikeDarkSouls

@shegotit I remember learning about blocking the alternative but not what video JY talks about it in. Can you link the video you're pulling your info from? I wanna make sure I undstand completely before I feel comfortable explaining it.

shegotit

@LSATisJustLikeDarkSouls said:
@shegotit I remember learning about blocking the alternative but not what video JY talks about it in. Can you link the video you're pulling your info from? I wanna make sure I undstand completely before I feel comfortable explaining it.

https://7sage.com/webinar/weaken-strengthen/

*She talked about blocking the alternative in correlation and causation questions