In Flaw / Descriptive Weakening questions, we approach the stimulus with a critical eye, looking for unreasonable assumptions and faulty reasoning methods. With practice, it’s often within reach to proactively identify the argument’s flaw well enough to move into the answer choices looking for that specific flaw.

This process is aided significantly by the fact that the LSAT writers routinely pull from a list of common flaws – learning to recognize these flaws when they appear in stimuli and answer choices will save you an enormous amount of time and mental energy.

Here’s a crisp way to think about the argument and its flaw, generated with the help of hindsight:

The pool of Program kids includes both kinds of students (Rural and Urban). Some of the Program kids do Extracurriculars. So the Extracurriculars pool must also include both kinds of students.

Flaw: It doesn’t have to include some of each. Maybe the subset of Program kids who do Extracurriculars are all Urban kids. (ooOo! Maybe all the Rural kids have to drive home early because they live so far away!)

If you manage to boil the stimulus down to the above summary, criticizing it isn’t so hard. The hard part is turning this stimulus into a workable model in the first place. Here’s a realistic walkthrough of how you’d do that in a timed setting:

The stimulus’ first sentence includes two claims about intersecting sets (an all claim and a most(ish) claim), separated by a causal claim. So two different alarms should already be going off in your head: “is our flaw gonna be some invalid formal logic inference?” and “is our flaw gonna be about causation?”

And you should (aspire to) know that both these questions are likely to be answered by looking at the conclusion. Is the conclusion a claim about intersecting sets? (Like “some flips are flops.”) Is it a causal claim? (Like “this phenomenon occurs because of the blops.”)

For now, just file those questions away and keep reading – it’s very likely you’ll have to make another run through this stimulus once you’ve figured out where it’s going.

Sentence 2 is a “some” claim (in fact it’s two some claims), increasing the likelihood that this is one of those questions with all the diagrams and whatnot. Okay keep reading you’ll diagram later.

The last sentence (which, by the way, is the conclusion) is another “some” claim (actually also two some claims), and it’s not causal. So the causation stuff doesn’t matter. The flaw is gonna be related to the argument’s inferences, best understood through formal logic.

So let’s run back through and build our structure, starting with the conclusion.

(Note: These individual claims are actually simple enough that you can probably think about them in English on test day. We’re presenting them in formal logic here for your convenience, but if you want English versions, just look up in the stimulus.)

Conclusion pt. 1: Extracurricular ←some→ Rural
Conclusion pt. 2: Extracurricular ←some→ Urban

Starting with the conclusion is nice because it defines the argument’s scope – knowing our precise goal helps us cut out a bunch of irrelevant stuff unrelated to that goal. Let’s jump back to the first sentence, which includes two separate claims:

Premise 1: Rural → Program
Premise 2: Urban —most(ish)→ Program

Notice how we left the causal claim out? That’s because we now know it doesn’t lead anywhere. On to the second sentence:

Premise 3: Program ←some→ Extracurricular

Notice how we left the academic achievers concept out? That’s because we now know that doesn’t lead anywhere either.

Now we’re a lot closer to the distilled summary at the top of this explanation:

All the Rural kids and most(ish) of Urban kids are in the Program. Some of the Program kids are Extracurricular kids. So the Extracurricular group must include some Rural kids and some Urban kids.

Through the formal logic lens, we’re in a classic “chaining conditionals” situation: the conclusions say two concepts are linked (Rural/Urban and Extracurricular), and the premises try to establish a logical chain that leads from one to the other. This argument’s chains are:

Rural → Program ←some→ Extracurricular
Urban —most(ish)→ Program ←some→ Extracurricular

In Flaw questions involving lots of formal logic, you don’t need to get too technical in describing what went wrong unless the argument commits the specific “necessary vs. sufficient confusion” flaw (which this argument does not).

For our purposes, the important thing is to recognize that the “some” link between Program and Extracurricular is too weak to support a connection between Rural/Urban and Extracurricular.

So it’s enough to anticipate that our flaw will likely highlight the weak link between Program and Extracurricular. It’ll be something like “just because the Program group has both types of kids doesn’t mean any given subset of that group must have both types of kids.”

(Extra Credit: If you’re up to date on your valid argument forms and you have a big ol’ brain, you could say our Rural chain would work if the “some” claim came before the “all” claim, and our Urban chain would work(ish) if you added this: Urban –most(ish)→ Extracurricular. That would be a real flex.)