LSAT 109 | Section 3 | Logical Reasoning: Q18

LR Question 18 Explanation

QUESTION TEXT: Studies have shown that photosynthesis, the process…

QUESTION TYPE: Flawed Parallel Reasoning

CONCLUSION: Industrial carbon dioxide pollution is purely beneficial to agriculture and to humanity.

REASONING: High levels of CO2 leads to more photosynthesis. Plants grow using photosynthesis.

ANALYSIS: The argument has listed a benefit for plants from CO2 production. But it hasn’t shown that there are no downsides that might outweigh the benefit. We know in real life that more CO2 probably leads to higher temperatures or shifts in weather patterns that can harm agriculture.

The conclusion might be right. But the argument would have to examine potential downsides to be sure.

The structure is: a benefit is listed, and potential (and fairly obvious) downsides are not addressed.

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1. This is a bad argument. It makes the error of going to extremes. “If something is good, then even more of it must be even better!” The stimulus didn’t make this error. (it would have said: “therefore we should burn as much CO2 as we can to help agriculture”)
2. CORRECT. This is the same structure. A benefit of exercise is listed. The argument concludes that exercise is therefore good. But any potential harms of exercise aren’t addressed. And it’s fairly obvious that exercise can lead to injury.The conclusion might be right. But the argument needs to examine potential downsides.
3. This argument is ok. But it’s possible that we can avoid excess calorie consumption even without fasting. 
4. This makes the same error as A. Just because one thing is better doesn’t mean we should completely eliminate the other thing. It might still be good, but in smaller quantities. 
5. This appears to parallel the argument. However, this argument focusses on one negative effect and ignores known positives of penicillin. The argument focussed on one positive effect and ignored known negatives of CO2.