PrepTest 121

Incorrect. This answer describes a correlation/causation flaw, but since the argument establishes a causal relationship between rain and an increase in mosquito populations ("leads to"), this answer is incorrect.

Incorrect. There's no discussion of an outcome being desirable. That said, lowering the rate of a disease can almost always be assumed to be desirable for the purposes of the LSAT.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
April/May rain usually increases mosquitoes, which increases encephalitis risk. You can't change the weather, so you can't lower your encephalitis risk.

Answer Anticipation:
The argument here has a couple logical elements that show up a lot on the LSAT—causality ("leads to") and comparisons ("increase", "increased", "decrease").

Usually when causality shows up in an Errors in Reasoning question, it's as a part of a correlation/causation flaw. However, in this case, the premises include causality, and there are no correlative premises, so we have to look elsewhere for the flaw. And since the causality is linked to those comparative words, that's unlikely to lead us to the correct answer, either.

Which brings us to another element in this argument that suggests a specific flaw—the strong nature of the conclusion. The conclusion is that people "cannot" decrease the threat of encephalitis—an absolute statement leaving no room for actions to have any impact on the likelihood. Do the premises bear out such a strong conclusion?

Well, there is an equally strong premise—humans cannot change the weather. So humans can't lower the risk of encephalitis by preventing a large amount of rainfall. However, that's a far cry from saying that there's nothing we can do to decrease mosquito populations and thus decrease the risk of encephalitis. Maybe we can directly kill the mosquito populations, or we can immunize people against the disease. Any answer highlighting that there are other potential means of lowering the threat will serve to point out the flaw in this argument.

Answer Explanation:
This answer highlights the possibility of lowering the risk of encephalitis through a means other than decreasing rain/controlling the weather. Since the argument treats weather control as the only means of achieving that goal, this answer highlights a possibility the argument ignores, and it's therefore correct.

Key Takeaway:
This argument highlights an interesting facet of a key concept on the LSAT—logical force. The conclusion is very strong ("cannot"), but there's a premise that's equally strong ("cannot"). However, the scope of the conclusion is wider than the scope of that premise. A strong conclusion needs a strong premise that also covers the same scope in order to be fully supported. When analyzing logical force in an argument, always check to see what that force is applied to. If a premise whose strength is being relied on to support the conclusion is more limited than that conclusion, the argument has a problem.

Incorrect. Since the conclusion is about "decreas[ing]" threat and not eliminating it, this answer about the threat "not occur[ring]" is out of scope.

Incorrect. First, if a premise establishes something is the case, then it supports a conclusion that it is possible—something that happens is possible. Second, the argument concludes that something is impossible based on a premise about what is impossible. There's just a shift in what it's talking about there that makes the argument flawed.