PrepTest 154

Incorrect. This answer choice reflects an illegal reversal of the first conditional, but, as we saw, the argument correctly applies the contrapositive of that statement to reach a valid intermediate conclusion.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Lots of gnats → Gecko lizards
Gnats → Wet climates
not Gecko lizards here, therefore not Lots of gnats, and therefore not Wet.

Answer Anticipation:
Diagramming this out, we can see two things. First, the intermediate conclusion is valid—if there aren't geckos living in an area, then, according to that first conditional, there aren't a lot of gnats. However, that conclusion doesn't justify the main point that the area isn't wet—that's an illegal negation of the second conditional, so that's what we should look for in the answer choices.

Answer Explanation:
While this answer choice sounds more like an illegal reversal of that second conditional than a negation, it does correctly describe the flaw. The argument does assume that Wet climates → Lots of gnats, meaning that not Lots of gnats → not Wet climate, which is the illegal negation we anticipated. Since this argument presents an assumption of the argument, it's correct.

Key Takeaway:
Errors in Reasoning questions will, occasionally, feature some valid conditional logic, which is why you can't simply see conditional logic and head straight to the answer choices—you need to understand if that conditional logic is applied in an invalid manner, and what manner it's incorrectly applied in.

Incorrect. The conditional establishes that gnats—not large populations of gnats—can't survive in wet climates, so it rules this possibility out.

Incorrect. The argument never establishes that the geckos need gnats because they eat them! While that's the most likely situation, we point that out to highlight that this answer brings up a consideration that is out of scope. Additionally, this answer reflects a bit of a reversal of the first conditional, which states gnats are sufficient, not necessary, for gecko populations.

Incorrect. Since the argument doesn't limit the climates where geckos can live (they're anywhere there are a lot of gnats, but they could live in other places, as well), this answer is out of scope.