LSAT 60 - Section 3 - Question 23

The question stem reads: The flawed pattern of reasoning in which one of the following is most closely parallel to that in the argument above? This is a Parallel Flaw question.

The author states," A species in which mutations frequently occur will develop new evolutionary adaptations in each generation." We can translate this into lawgic to read:

Mutations Frequently Occur -> Develop Evolutionary Adaptations

The author then states the premise and conclusion, "Since species survive dramatic environmental changes only if they develop new evolutionary adaptions (premise), a species in which mutations occur frequently occur will survive drastic environmental changes (conclusion)." Let's translate those into lawgic:

Premise:
Survive Dramatic Environmental Changes -> Develop Evolutionary Adaptations

Conclusion:
Mutations Frequently Occur -> Survive Dramatic Environmental Changes.

We can combine the argument to read:

P1: Mutations Frequently Occur -> Develop Evolutionary Adaptations
P2: Survive Dramatic Environmental Changes -> Develop Evolutionary Adaptations
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C: Mutations Frequently Occur -> Survive Dramatic Environmental Changes

We can see that the author confused the sufficient and necessary conditions of P2. Evolutionary adaptations are a requirement to survive dramatic environmental changes, but there might be additional requirements, such as having enough food. Let's take the general form of the argument:

A -> C
B -> C
____________
A -> B

By that line of reasoning, we could conclude that all apples (A) are peaches (B) because all apples (A) are fruit (C), and all peaches (B) are fruit (C).

When evaluating an answer choice, we need two sufficient conditions pointing to the same necessary condition. We also need a conclusion that says one of those sufficient conditions is sufficient for the other sufficient condition. Now that we know what we are looking for let's turn to the answer choices.

Answer Choice (A) is incorrect. The first premise says: properly built -> stones support each other. So the next premise needs "stones supporting each other" for the necessary condition. However, we get: sturdy -> properly built. So we can stop reading there.

Answer Choice (B) is incorrect. The first premise says: play before a different audience -> never get the same reaction. So the next premise needs to have "never get the same reaction" for the necessary condition. However, we get: play -> always has a different audience. Like (A), we can stop reading there.

Correct Answer Choice (C) is what we discussed. The first premise says: perfectly honest -> always tell the truth. So the next premise needs "always tell the truth" in the necessary condition. The next premise says: morally upright -> always tell the truth. Ok, so that checks out. The conclusion has to say: perfectly honest -> morally upright, which is exactly what (C) says. So (C) is the right answer.

Answer Choice (D) is incorrect. The first premise says: garden productive -> soil well drained. So the next premise needs "soil well drained" in the necessary condition. However, we get: soil well drained -> good soil. So we can eliminate (D).

Answer Choice (E) is incorrect. The forest premise says: diet healthful -> well balanced. So the next premise needs to have "well balanced" in the necessary condition. However, the next premise says: well-balanced -> includes fruit and vegetables. So we can eliminate (E).