LSAT Explanation PT 36, S3, Q19: My father likes turnips, but not

LSAT Question Stem

The flawed reasoning in the argument above most closely resembles that in which one of the following? 

Logical Reasoning Question Type

This is a Parallel Flaw question. 

Correct Answer

The correct answer to this question is B. 

LSAT Question Complete Explanation

Let's first analyze the argument in the passage. The passage states that the father likes turnips but not potatoes, which he finds tasteless. The conclusion drawn is that it is not true that whoever likes potatoes likes turnips. This is a flawed argument because it only considers one case (the father) and doesn't provide any information about people who like potatoes. We can label the parts of the argument as follows:

Premise: Father likes turnips but not potatoes.

Conclusion: It is not true that whoever likes potatoes likes turnips.

To make this more understandable, let's use a simple example. Imagine we have a group of people who like apples and a group of people who like oranges. Just because one person likes apples but not oranges doesn't mean we can conclude that everyone who likes oranges doesn't like apples. We need more information about the preferences of the orange-likers to make a valid conclusion.

An "Evaluate" question for this argument could be: "Do we have information about the preferences of people who like potatoes?"

Now, let's discuss the question type and answer choices. This is a Parallel Flaw question, which asks us to find an answer choice that contains a similar flawed reasoning as the one in the passage.

a) This answer choice does not parallel the flaw in the passage. The argument in the passage is about one case (the father) and draws a conclusion about a different group (potato-likers). The argument in this answer choice is that a non-paperback book is expensive, so it is not true that some paperbacks are expensive. This argument is different from the one in the passage, as it does not involve two separate groups.

b) This is the correct answer choice. The flawed reasoning in this argument is similar to the one in the passage. The argument states that a recently published work of fiction has more than 75 pages but is not a novel, so it is not the case that all novels have more than 75 pages. Just like in the passage, this argument considers one case (the work of fiction) and draws a conclusion about a different group (novels) without providing information about that group.

c) This answer choice is not flawed and therefore does not parallel the flawed reasoning in the passage. If all ornate buildings were constructed before the twentieth century and this house is ornate, it is valid to conclude that the house was built before the twentieth century.

d) This answer choice also contains valid reasoning and does not parallel the flawed reasoning in the passage. If Erica enjoys studying physics but not pure mathematics, it is valid to conclude that not everyone who enjoys studying physics enjoys studying pure mathematics.

e) This answer choice does not parallel the flawed reasoning in the passage. Instead, it represents a Mistaken Reversal. The conditional rule is that people who do their own oil changes are car fanatics. The argument incorrectly reverses this rule and concludes that the neighbors, who are car fanatics, must do their own oil changes.