LSAT 67, Logical Reasoning I, Q9, LSATHacks

LR Question 9 Explanation, by LSATHacks

QUESTION TEXT: To use the pool at City Gym, one must have a membership…

QUESTION TYPE: Flawed Reasoning

CONCLUSION: Sarah must use the pool at least sometimes.

REASONING: Sarah has a membership, and only members can use the pool.

ANALYSIS: Classic error. This argument confuses a necessary condition for a sufficient condition. If you got this wrong, repeat this question later. This error will show up elsewhere. Here’s the premise:

Can use pool ➞ Member

Sarah is a member. But just because Sarah can use the pool doesn’t mean she will. I’ll use an analogy. You could surely scrape enough money together to visit Guyana. Flights are cheap – why not go to Central America? You could.

But, you probably won’t fly to Guyana. Just because you can do something (i.e. you meet the necessary conditions), doesn’t mean you will.

The right answer is hard to understand. That doesn’t give you an excuse to skip it. Instead, break it down part by part until you reach a section you understand. Then expand out from there.

___________

1. The stimulus doesn’t mention enforcement.
2. CORRECT. This is hard to understand, but it means the author mistook a necessary condition for a sufficient condition.
   Truth is required for the conclusion = necessary
   Truth ensures the conclusion = sufficient
3. The stimulus didn’t mention alternatives. This is a different mistake. It’s like saying: ‘Obama and Romney are the only two candidates for president, so one of them will be elected.’ I didn’t exclude alternatives, such as one of them resigning and being replaced.
4. There’s no group mentioned. Sarah definitely has the attribute of ‘having a membership’.
5. This is code for ‘circular reasoning’. The argument isn’t circular. Instead, it mistakes necessary for sufficient.