Logical reasoning PrepTest 129 · Section 3 · Question 24

Incorrect. This answer doesn't guarantee that any animal with a contracting vessel (such as the lancelet) has a heart—just that only animals with a contracting vessel have a heart. In other words, the lancelet has a necessary condition for having a heart, but not a sufficient one, so this answer doesn't justify the conclusion that the lancelet has a heart.

Incorrect. What other animals are widely held to have doesn't determine whether the lancelet has a heart.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Sufficient Premise

Stimulus Summary:
The lancelet's vessel that's considered an artery looks like a heart, and acts like a heart, so it's a heart.

Answer Anticipation:
This argument relies on comparing the vessel in a lancelet to the heart of other animals in two areas—the structure and the way it works. Since the vessel is similar to animal hearts in these two ways, it concludes that it is a heart. However, the argument never actually defines what a heart is, and it certainly doesn't state that anything resembling a heart's structure and how it works is a heart. In making that jump, the argument assumes that anything that looks like and acts like a heart is a heart, so the correct answer should establish that connection.

Answer Explanation:
This answer connects the points of comparison between the lancelet's vessel and other animal hearts to being a heart. Since the lancelet vessel has a structure and action that resembles the heart of other animals, this answer justifies the conclusion that it's a heart.

Key Takeaway:
First, in Strengthen with Sufficient Premise questions, the correct answer will need to justify the conclusion—so make sure that the answer you select is strong enough to do so, and it doesn't reverse the connection required by the stimulus (as the many answers here did that raised a necessary condition for having a heart, not a sufficient condition).

Second, comparisons are one of the key types of logic on the LSAT! When they feature heavily in a stimulus, they're likely to play into the correct answer.

Incorrect. This answer establishes a necessary condition to be a heart, but not a sufficient condition, so it can't justify a conclusion that a vessel is a heart (just that it isn't one).

Incorrect. This answer can be rephrased as, "If you have a heart, then you have an artery." However, it can't be used to justify a conclusion that something has a heart—again, it only establishes a necessary condition for a heart, not a sufficient one.