LSAT Explanation PT 26, S2, Q20: Martha's friend, who is very knowledgeable

LSAT Question Stem

Which one of the following has a flawed pattern of reasoning most like that in Martha's reasoning? 

Logical Reasoning Question Type

This is a Parallel Flaw question. 

Correct Answer

The correct answer to this question is C. 

LSAT Question Complete Explanation

Let's first analyze the argument in the passage. Martha's friend tells her that there are no edible daisies, at least not any that are palatable. Martha, however, reasons that since there are daisies that are a kind of chrysanthemum and there are edible chrysanthemums that are quite palatable, her friend must be incorrect. The structure of the argument can be broken down as follows:

Premise 1: Some daisies are a kind of chrysanthemum.

Premise 2: Some chrysanthemums are edible and palatable.

Conclusion: Martha's friend is incorrect, and there must be some edible and palatable daisies.

The flaw in this argument is that it assumes that the two groups (daisies and edible chrysanthemums) must overlap just because they are both part of a larger group (chrysanthemums). However, there is no evidence to support this assumption.

An "Evaluate" question for this argument could be: "Do the edible and palatable chrysanthemums include any daisies?"

Now, let's discuss the question type and answer choices. This is a Parallel Flaw (PF) question, which asks us to identify the answer choice with a flawed pattern of reasoning most like that in Martha's reasoning. The correct answer is C.

a) This answer choice assumes that if the whole (city chorus) is renowned, a part of it (Jeanne) must also be excellent. This is not the same flaw as in the passage, where the assumption is that two groups must overlap because they are part of a larger group.

b) This answer choice is valid, as it states that all members of the library reading group are avid readers, and Rolfe is a member of the group. Therefore, Rolfe must be an avid reader. This does not exhibit the same flaw as the passage.

c) This answer choice exhibits the same flaw as the passage. It assumes that because some of Noriko's sisters are on the debate team and some members of the debate team are poor students, there must be an overlap between these two groups (i.e., at least one of Noriko's sisters must be a poor student). We don't know if the groups overlap, so this answer choice is correct.

d) This answer choice states that most of Leon's friends are good swimmers, and all good swimmers are quite strong. Therefore, it is likely that at least some of Leon's friends are quite strong. This answer choice does not exhibit the same flaw as the passage since there is a direct link between good swimmers and being quite strong.

e) This answer choice introduces new information in the conclusion (that some of Teresa's colleagues are good writers), which is not the same flaw as in the passage. The passage's flaw assumes that two groups must overlap because they are part of a larger group, whereas this answer choice does not exhibit that flaw.

In conclusion, the correct answer is C, as it exhibits the same flaw as the passage, assuming that two groups must overlap because they are part of a larger group.