LSAT PrepTest 13 - Section 4 - Question 15

Hide analysis

Support At Flordyce University any student who wants to participate in a certain archaeological dig is eligible to do so but only if the student has taken at least one archaeology course and has shown an interest in the field. ████ ████████ ███ ████ █████ ██ ████████ ██ ███████████ █████ ████ ████ ███ ███████████ ███████ ██████████ ████ ████████ ███ ████ ██ ███████████ ██ ███ ███ ████ ██ ██████████ ██ ██ ███

Summary: Diagramming Flawed Reasoning Pattern

There's a lot going on here. We're given a sufficient condition: any student who wants to participate in this dig is eligible to do so.

want to participate → eligible

But we're also given two necessary conditions: students who want to participate are eligible to do so only if they have taken at least one archaeology course and have shown interest in archaeology.

eligible → taken course AND shown interest

We're then told that many students who have shown interest in archaeology never take an archaeology course. (Remember that for the LSAT, we can usually diagram "many" as "some").

shown interest ←s→ /take course

Therefore, the author concludes, many students who want to participate in the dig will be ineligible:

want to participate ←s→ /eligible

15.

The flawed reasoning of which ███ ██ ███ █████████ █████████ ██ ████ ███████ ██ ████ ██ ███ ████████ ██████

Question Type

Parallel flawed method of reasoning

If you're struggling to figure out how to pin down the flaw with your diagrams, you're not alone. The key is figuring out how the "sufficient condition" (want to participate → eligible) and the "necessary conditions" (eligible → taken course AND shown interest) fit together. To figure this out, it might actually help to stop thinking in terms of Lawgic diagrams and just think in terms of sets: what subset of the larger set of "students" are we actually interested in?

The answer to this comes from what we called the sufficient condition: students who want to participate in the dig. This is actually the only group of students we're interested in at all throughout this argument. We're not interested in any students who don't want to participate in the dig, and we only care about students who have taken at least one archaeology course and/or have shown interest in archaeology if they also want to participate in this dig.

This helps us see where the flaw is. Maybe it's true that in general there are many students who have shown interest in archaeology but will never take an archaeology class. This doesn't matter to us because we don't know if any of these students want to participate in this particular dig. Maybe none of these "many" students want to participate in the dig, in which case we don't care about these students. And we certainly can't conclude that because some students exist in general who don't meet both necessary conditions, there must be some students who want to participate in the dig who don't meet both necessary conditions.

In other words, the flaw pattern in the argument is that it gives us a specific subset of a larger group (students who want to participate in this dig), tells us two necessary conditions that only matter for that subset, then tells us that because some members of the larger group (all students) don't meet both necessary conditions, some members of the subset must also not meet both conditions.

Theoretically, any jar ██ █████ ██████ ██████████ ██ ███ █████ ███ ████ ██ ██ ███ █ ████ ██████████ █████ ████ ████ ███ ████ ███ ██ ████ █████ █████ ███ ███████ █████ ██ ███ ████ ███ ████████ ███ █████ ███████

Incorrect. (A) tells us about a general set (jars), then gives us a condition for those jars to be worth saving: they must have lids. We are then told that some jars don't have lids, and then somehow reach the conclusion that some sizes of jars (some subsets of the larger set of jars) aren't worth saving. This is a flawed argument, but a different pattern from the stimulus.

For a horse ████ ██ ████ ████████ ██ ██ █████ ███ █████████ ██████ ████ █████ ████ ████ ██ ██████████ ███ ███████ ████ ██████ ████ ███ ██████████ ███ ███ ███████ █████████ ████ █████████████ ██████ ███ ███ █████ ███ █████████ ███████

Correct. Like the stimulus, (B) gives us a subset we're actually interested in: we're not interested in all horses; we're interested in "well schooled" horses. We're given two necessary conditions (being surefooted and gentle) that matter for members of this subset. Then we're told that some members of the larger group (all horses) don't meet both necessary conditions. The argument therefore concludes that some members of the subset (well schooled horses) must also fail those conditions.

78%

If an author’s █████ █████ ███ █ ████████ ███████ ███ █ ███████████ █████ ██ ████ ██████ █ ████████████ █████ ████ ██████████ █████ ██████ ████ ████████ ███ ████ █████ ██████ ██████ █████████████

Incorrect. The set we're interested in for (C) is "first novels." (C) gives us two sufficient conditions for members of this set to become best-sellers, then tells us that many members of the set don't meet either condition. The conclusion is that not many of these first novels become best-sellers. If there's any flaw here, it would depend on the meaning of "many". But in any case, this would be a different flaw pattern than in the stimulus.

Any automobile that ██ ████ ████ █ ███ █████ ███ ██ ██████████ ████ ██ ████ ███████ ██ ██ ██ ███ █████████ ███████████ ████ ███████████ ███ ████ ████ █ ███ █████ ████ ███ █████ ██ ███ ████ ████████ ██████████ ████ ███████████ ███ █████████ ███████████

Incorrect. The set (D) talks about is "automobiles that are more than a few years old." For members of this set, we're told they need repairs if they are not regularly maintained:

/maintained → need repairs

Then we're told that many members of this set still don't need repairs. The conclusion is that many automobiles are regularly maintained, which follows from the contrapositive of the statement above:

/need repairs → maintained

There's no flaw in this argument.

An expensive new ████████ ████ █████ ██ ██ █ ████ ██████████ ████ ██ ██ ██ █████████████ ████████ ██ ████████ ████ ██ ██████ ██████ ████████ █████ ████ █████████ ███ █████████ ███ ███ █████████████ █████████ ███ █████████ ███ █████████ ████ █████ ██ ██ ████ ████████████

Incorrect. The set we're interested in for (E) is "expensive new buildings." However, instead of being told two conditions that are both necessary for members of this set to obtain a certain result, we're given two options: for these buildings to be good investments, they must be either aesthetically pleasing or provide lots of office space.

We're then told that members of this specific subset (not members of the larger group of all buildings) don't meet one of these two options, and the conclusion is that most of these buildings will not be good investments. The flaw here comes from forgetting that these buildings could still fulfill the other option for a necessary condition, having lots of office space. But this is a different flaw pattern than in the stimulus.

Answer five questions and we'll estimate your score.

It takes about five minutes.

Take the free diagnostic

More free LSAT prep: Sample LSAT questions Full-length diagnostic & practice test All free LSAT resources

PrepTest 13 - Section 4 - Question 15

Answer five questions and we'll estimate your score.

Difficulty

Analysis

Answer Popularity

Question history

Confirm action

PrepTest 13 - Section 4 - Question 15

Answer five questions and we'll estimate your score.

Difficulty

Analysis

Answer Popularity

Question history

Want to know why the right answer is right?