#17 - A large amount of rainfall in April and May typically

[Administrator]

Complete Question Explanation

Flaw in the Reasoning—CE. The correct answer choice is (C)

The author of this stimulus makes a flawed causal argument:

Premises:

• A lot of rain usually causes more mosquitoes.
  
  More mosquitoes cause an increased threat of encephalitis.
  
  We can’t control the weather.

Flawed conclusion:

• There is no way to decrease the threat of encephalitis.

While we cannot control the weather, the author seems to have disregarded the mid-step cause—that of mosquitoes. Even if we cannot control rainfall, perhaps there are other ways to control the mosquito population, and thus the threat of encephalitis.

Answer choice (A): This answer choice presents a particular type of causal flaw, but not the one reflected in this stimulus, so this answer choice is incorrect.

Answer choice (B): This would not be a flaw—the presumption that a decrease in the threat of encephalitis would be reasonable—but there is no such presumption made anyway, so this answer choice is also incorrect.

Answer choice (C): This is the correct answer choice. The author disregards the fact that there may be other ways to control the mosquito population.

Answer choice (D): The author does not make any such presumptions, so this answer choice cannot be correct. It is irrelevant to consider that the threat of encephalitis might increase in the absence of mosquitoes—the argument is that we cannot decrease the threat, not maintain it.

Answer choice (E): It is not necessarily a flaw to base a conclusion about what is possible on factual premises, but this is not done in this stimulus regardless, so this answer choice is incorrect.

[prep88]

Hey guys,

My diagram for this Causal stimulus is... "heavy rainfall mosquito encephalitis"; if the author takes for granted the heavy rainfall, doesn't it per se guarantee the encephalitis via the Causal chain? I don't get why is this argument flawed. My prephrase was that it is flawed because the author takes it for granted that the rainfall will be heavy.
Anyone?

Thank you!

[Dave Killoran]

Hey Prep,

Thanks for the question! To see where this argument runs into problems, let's first separate out the premises from the conclusion.

As you rightly note, there's a causal chain in the premises: heavy rainfall mosquito encephalitis. But, recall that causality in the premises is not typically an issue; the author is allowed to state a causal premise and then work from there. So, an answer like (A) is incorrect because the doesn't take this for granted; he or she states it clearly and he/she is allowed to do that.

Next, we have the premise that "People cannot change the weather." Ok, fine there for the most part. But, does the causal chain and the fact that we can't change the weather suddenly add up to the conclusion that "people cannot decrease the threat of encephalitis" ? No, and that jump from the premises to the conclusion is where we have a flaw that we need to identify.

Why is it flawed? Because while bad weather may give rise to a greater threat, there may also be other ways to control (and thus decrease) that threat. For example, I lived in Minnesota during high school, and every spring and early summer there they spray for mosquitoes, and they also seed the marshes with anti-mosquito pesticides to control breeding. That's not controlling the weather, but it does reduce the prevalence of mosquitoes, and in a scenario like the one in the stimulus, it would reduce the threat of encephalitis.

So, the flaw here is thinking that while a factor (rain) creates an effect (increased threat), that there is no way to mitigate that effect through other means. That problem is best described in answer choice (C).

In response to your prephrase, I'd say we should look closely at the stimulus. The author just says "a large amount of rainfall...typically leads to..." and uses that to discuss our inability to control the weather and then the threat. It's not that the author takes for granted that next April and May will have heavy rainfall, just that when it occurs we have these problems (and the judgments made thereafter are where we get our flaw). And LSAC would say that it is a reasonable commonsense assumption that occasionally in April/May you will have heavy rainfall.

The good news is that you are prephrasing, and talking about problems like this is how we slowly get better at seeing what's occurring. Even the discussion of causality in the premises vs causality in the conclusion can have a big impact on how you see these problems going forward. Keep working at it!

Please let me know if that helps. Thanks!

[prep88]

Hi Dave,

I really appreciate your response, this really helps! I got confused with this question because of the idea that causal relationships are perceived to be absolute and I missed the language here. Would it be different here if we replace "rainfall USUALLY causes mosquitos" with "rainfall causes"? and "causes increased threat of encephalitis" with "causes encephalitis" Would it mean that mosquitos are always caused by rainfall and nothing else? and that encephalitis is caused by mosquitos and nothing else?

Thank you!

[Dave Killoran]

Great, glad to help! No, I don't think those changes would have a huge effect here. Yes, they would make the argument more rigid (and unrealistic), but the "usually" and "threat" aren't really the biggest issue here. Why is that? Because they occur in the premises. LSAT authors are allowed to start with any premises they want to start with. Errors of reasoning occur when you go from premise to conclusion. The conclusion in this argument doesn't match with the premises, and that's where the error is.

One of the big problems with causality comes when an author draws a really rigid conclusion based just on a correlation in the premises. That's where you often see this absolute language that A causes B. If an author does that with a premise, it's not a problem (and some causal premises are absolute with good reason. For example: "Jumping from the top of the Empire State building to the street below will cause you to die.").

Please let me know if that helps. Thanks!

[prep88]

I got it, thanks!

[JocelynL]

Hello,
I'm just looking to understand what answer choice A is saying. Is it describing a scenario where a correlation relationship is confused for a causal relationship?
thanks,

[KelseyWoods]

Hi Jocelyn!

Answer choice (A) is describing another common way that authors make flawed causal arguments--by confusing a temporal relationship for a causal one. Sometimes an author will say something like "A happened and then B happened. So therefore A caused B to happen." But just because one event happened before another event, that is not enough to definitively prove that the first event caused the second event.

Hope this helps!

Best,
Kelsey