LSAT Discussion Forum

Complete Question Explanation

Assumption. The correct answer choice is (E)

The stimulus is about Kim’s argument which concerns electric cars versus traditional gas powered cars. Her conclusion (the last sentence) is that even if all gas-powered cars were replaced with electric cars fossil fuel pollution would not decrease, it would just be replacing one source of pollution for another.

The premises that she uses to support this conclusion are:

• 1. “It takes electricity to recharge batteries and most of our electricity is generated by burning polluting fossil fuels.”
  
  2. Increasing the number of electric cars would cause an increase in the number of power plants since current ones are running at maximum capacity.

The question is an assumption question and because Kim’s argument does not have any obvious flaws or gaps, we can probably guess that this will be a Defender type question.

Answer Choice (A): This is irrelevant as the argument in the stimulus does not depend on whether or not the total number of cars on the road increase or decrease. What we already know is that Kim has already accounted for an increase in the number of electric cars, which can be found in the third sentence of the stimulus. And that is all that is needed for her conclusion to be valid.

Answer Choice (B): Once again an irrelevant assumption. Nowhere in the stimulus does Kim make any claims about how significantly do gas powered cars contribute to fossil fuel pollution. This does not affect the conclusion that electric cars produce fossil fuel pollution through power plants.

Answer Choice (C): This answer choice may be tempting but we have to be aware of what the conclusion actually is. Kim does not make any claims about whether it is right to replace gas powered cars with electric ones; she just concludes that electric cars would contribute to fossil fuel pollution. And so we see that this is not a necessary assumption.

Answer Choice (D): Another unnecessary assumption. We don’t care if electric cars pollute while being operated; that is not the issue. The argument rests on the idea that the pollution comes from the power plants that will be built to supply the electric cars.

Answer Choice (E): This is the correct answer choice. Kim’s conclusion is based on the premise that fossil fuel pollution will remain relatively the same because electric cars would necessitate the building of more power plants. In turn these power plants would contribute to fossil fuel pollution because they burn fossil fuels. And that is where the assumption lies: That at least some of these new plants would burn fossil fuels. Negating (E) by saying that “None of the generating facilities built…would be a type that burns fossil fuel,” severely weakens the conclusion because if they don’t burn fossil fuel they clearly won’t be contributing to fossil fuel pollution.

Hi,

How would you correctly negate answer choice (C)? Also, if (C) was the correct answer, what would the author's conclusion look like in this stimulus?

Thank you!

Hi rpark,

To negate a conditional statement, you should negate the necessity of the relationship expressed. That is, say that the necessary condition does not have to be there for the sufficient condition to occur.

In this case, I would phrase the negation of answer choice (C) as "It would be justified to replace gas-powered cars with battery-powered cars, whether or not electric cars produce less air pollution."

Your second question is a bit more difficult to answer. I would expect answer choice (C) to be a necessary assumption for an argument that concludes that replacing gas-powered cars with battery-powered cars is not justified or not the right thing to do. Furthermore the speaker would have also had to offer a premise or an intermediate conclusion about the relative air-pollution rates of both types of cars as evidence.

I thought the final sentence was a subsidiary conclusion? Why did set that as the main conclusion?
Since the main point is not stated, but can be inferred right?

Generally speaking, LSAT2018, the Main Point will be something the author said, not something we infer. We can infer here that Kim thinks electric cars are not, in fact, a potential solution to the problem of air pollution, but since she didn't actually say it, that is not her Main Point in this stimulus.

That said, once in a while the LSAT will ask us for a Main Point that is neither explicitly stated in the stimulus nor a paraphrase of the claims in the stimulus. In those cases there is typically just a fact set in the stimulus, and we can treat those rare questions like Must Be True questions and draw an inference as our prephrase and answer choice. But those are rare. When you are presented with a complete argument, with premises and at least one explicit conclusion, as we have here, you can and should treat the explicit conclusion as the main point.

Not that it matters much in this case, since it is an assumption question rather than a main point question! If it had been a main point question, then we would have had to worry about the finer points of the answer choices, and would have perhaps run into a scenario where someone might have a valid complaint to LSAC about an unfair or improper question depending on what answer choices we were given to work with. Thank goodness we don't have to worry about that here, and can instead focus on the question they did ask.