LSAT Explanation PT 33, S3, Q18: Studies have shown that photosynthesis, the

LSAT Question Stem

The flawed reasoning in the argument above is most similar to 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

First, let's analyze the argument in the passage. The passage states that studies have shown that photosynthesis is intensified with increased carbon dioxide levels, which are caused by burning fossil fuels and other human industrial activities. The author concludes that these industrial activities are purely beneficial to agriculture and those who depend on it. The structure of the argument is as follows:

Premise: Photosynthesis is intensified with increased carbon dioxide levels.

Premise: Burning fossil fuels and other human industrial activities increase carbon dioxide levels.

Conclusion: These industrial activities are purely beneficial to agriculture and those who depend on it.

The flaw in this argument is that it assumes that if something has one beneficial effect (intensifying photosynthesis), it must be purely beneficial and have no negative effects. This is a "some evidence" flaw. To illustrate this with a simple example, let's say eating ice cream makes people happy. This does not mean that eating ice cream is purely beneficial, as it could also have negative effects, such as weight gain or tooth decay.

An "Evaluate" question for this argument could be: "Are there any negative effects of increased carbon dioxide levels on agriculture or those who depend on it?"

Now, let's discuss the question type and the answer choices. This is a Parallel Flaw (PF) question, which asks us to identify the answer choice that contains reasoning most similar to the flawed reasoning in the passage.

a) This answer choice states that because a high fiber diet is more healthful than a low fiber diet, a diet consisting entirely of high fiber foods would be even more healthful. This is not a match because it does not assume that something is purely beneficial based on one positive effect.

b) This answer choice states that because exercise prevents diseases, injuries, and other human ills, it must be purely good and have no negative effects. This matches the flawed reasoning in the passage, as it assumes that if something has one beneficial effect, it must be purely beneficial. This is the correct answer.

c) This answer choice states that consuming more calories than one expends leads to weight gain, so to avoid health problems, one should fast periodically. This does not match the flaw in the passage because it does not assume that something is purely beneficial based on one positive effect.

d) This answer choice states that one can obtain more vitamins and minerals from fresh fruits and vegetables than from processed ones, so one should abandon consumption of processed fruits and vegetables in favor of fresh ones. This does not match the flaw in the passage because it does not assume that something is purely beneficial based on one positive effect.

e) This answer choice states that excessive use of penicillin increases susceptibility to penicillin-resistant infections, so the best policy is to avoid using penicillin to strengthen the body's innate ability to resist disease. This does not match the flaw in the passage because it does not assume that something is purely beneficial based on one positive effect.

In conclusion, the correct answer is B, as it contains reasoning most similar to the flawed reasoning in the passage.