Logical reasoning PrepTest 121 · Section 1 · Question 17

Incorrect. The successful group of animals is noted as having spread to "virtually every" ecosystem—which would include the geographically isolated areas. As such, it's not a problem for the argument if those areas are geographically isolated, so the argument doesn't assume that they aren't.

Incorrect. The stimulus notes that insects are of the successful class that has spread to virtually every ecosystem, and ants are a particularly successful subcategory of this class. So it's assuming that ants and other insects are similar—ants just take it up a notch.

Incorrect. This answer establishes a necessary condition for avoiding being threatened, not a sufficient condition (Avoid being threatened → Spread into virtually every ecosystem—"the only" introduces a sufficient condition). As such, it can't justify the conclusion that ants aren't threatened, and thus it isn't something assumed by the argument.

Incorrect. This answer describes a Part vs. Whole flaw, but one that goes from the part to the whole. The stimulus, however, goes from the whole (all ants) to the part (individual ant species).

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Insects are so successful they've spread to all ecosystems. Ants are the most successful. Therefore, no ant species is threatened.

Answer Anticipation:
This is an interesting example of a common flaw!

Let's focus on just the relevant information, as this argument goes out of its way to start broad but end up very small (because ants, get it!). If we work backwards from the conclusion, we can see that it's about only ants, so we should focus our understanding there.

What do we know about ants based on the premises? They're particularly successful and have spread into virtually every ecosystem. That's the premise used to support the conclusion that no species is threatened.

So since ants generally have spread to all ecosystems, it must be the case that each individual species isn't threatened—because they've presumably spread out quite a bit, as well. But that's assuming what is true of ants generally is also true of each species of ant—a jump from a whole to a part.

What's interesting here is that the "part" is also a group—a species is a collection of a certain type of ant. However, all of the species also form a broader "whole." Just because something can itself be described as a group doesn't mean it can't also be a part—and so we have a Part vs. Whole flaw here. Specifically, we go from the whole (ants) to the part (individual species of ant).

Answer Explanation:
This answer describes the correct Part vs. Whole flaw. The whole (all ants) aren't threatened as they've successfully spread into virtually every ecosystem, so the parts (each species of ant) are similarly not threatened.

Key Takeaway:
This is a rare example of a "part" in a Part vs. Whole flaw itself being able to be viewed as a "whole" or a group. While not something you should be generally looking for, it's good to take away from this question that something like this can happen, and you should consider the relationship between the elements, and if you can describe one as being a part of another, don't worry if it could be considered a whole in another context!