Critical Reasoning

Testluv wrote:
Hi Sunnyjohn,

In order to be "useful" in evaluating the argument an answer choice has to fall directly within the scope of the argument. Accordingly, in evaluate the argument or relevant information questions it is important to determine the author's central assumption. The correct answer will always be closely related to the author's assumption.

It is also useful to view these questions as being hybrid strengthen/weaken. The answer choices will often be questions. Here, all of the answer choices begin with "whether." Ask of each answer choice whether it is the case or whether it is not. The correct answer will be something where if it goes one way, it will strengthen the argument, and if it goes another way, it will weaken the argument.

Here, the author has two main pieces of evidence: 1) most of the world's supply of uranium currently comes from mines and 2) it is costly to extract uranium from the sea. He uses these two pieces of evidence to conclude that this method will remain commercially unviable (unless the cost can be reduced).

Let's look at choices A and C:

a. Whether the uranium in deposits on land is rapidly being depleted

Well, what if uranium from land was not being depleted? Then the argument is strengthened, as the supply of coal won't be diminished, and so there will be no (economic) reason to turn to the sea.

And what if uranium from land WAS being rapidly depleted? Then the supply of coal would dry up, coal prices would most likely go up, and all of a sudden it might be commercially viable (profitable) to mine coal from the sea--the argument is weakened.

In fact, this answer choice is essentially the author's assumption. It is a necessary assumption of the argument that the coal from mines continue to provide a ready supply. Denial test: if coal from mines dried up, it may well be economically (commercially) viable to turn to the sea, and the argument falls apart. Figuring out the assumption before going to the answer choices is of huge benefit in these questions. Remember you can always verify
whether you've figured out the necessary assumption correctly by applying the denial test.

c. Whether there are any technological advances that show promise of reducing the costs of extracting uranium from seawater

Well, what if there were? The author would simply remind you that he said "..until the cost of extracting uranium from seawater can somehow be reduced..." The author acknowledged that mining coal from the sea might be worth it if they could figure out a cheaper way of doing it. Therefore, determining whether there are any technological advances that could make it cheaper would not be very useful in evaluating the merits of his argument.

Stacey Koprince wrote:Received a PM asking me to respond. I see that testluv has already given an answer that many liked, but I haven't read it (on purpose - I don't want to be swayed by testluv's explanation!). I'll just work through it myself; that'll give people a second perspective, which is sometimes valuable.

"Evaluate the Conclusion" is a minor-type CR question. We should expect the argument to make a claim (that is, we need to find the conclusion), and the correct answer will be some piece of additional info that, IF we knew it, would help to evaluate whether the conclusion is valid. The additional piece of info would NOT necessarily serve to make the conclusion valid. Rather, the question is "is this conclusion valid?" and the correct answer would help to answer that question.

Eg, let's say that I claim "To Kill A Mockingbird is the best book in the world." How could we evalute that claim? Well, what if there are three big surveys every year in which millions of people are asked what they think is the best book in the world. If we could know the results of those surveys, then we could better evaluate my claim. (Note that we wouldn't know whether my claim is valid or is not valid until we actually did see the results of the surveys - but, either way, the survey results will help to decide whether my claim is valid.)

Argument:
most ur. comes from mines
ur. can come from sea water
BUT that costs more than you can sell it for
CONC: not "viable" to get ur. from sea water unless cost of extraction is reduced.

[thought: what about raising the price that it sells for? if that goes higher than the cost of extracting from sea water... then no problem.]

We can rephrase the conc as:
if cost of extraction is NOT reduced, then it will NOT be economically viable to get ur. from sea water

The author is making a cause-effect claim. Our task is to see whether any of the answers will make a difference in terms of whether the cause (cost of extraction is not reduced) will actually lead to the effect (not viable to get ur. from sea water). The correct answer should be able to take us in two directions: one way, the conclusion does look valid (or, at least, as valid as it was in the first place), the other way, the conclusion does not look valid.

People were mostly debating between A and C, so let's eliminate the other three first.
B) if it IS used near where it was mined, what effect does that have on the economic viability of getting ur. from sea water? What about if it is NOT used near where it was mined? Either way, doesn't change the fundamental situation: it's still viable to use land ur. and not viable to use sea ur. Eliminate.
D) If seawater ur. volume is much greater, what effect does that have on the economic viability of getting ur. from sea water? What about if seawater ur. volume is not much greater? Either way, doesn't change the fundamental situation: it's still viable to use land ur. and not viable to use sea ur. Eliminate.
E) If sea and fresh ur. is similar, what effect does that have on the economic viability of getting ur. from sea water? What about if the costs are not similar? Either way, doesn't change the fundamental situation: it's still viable to use land ur. and not viable to use sea ur. Eliminate.

So, see what I did with each of those? I tested each side of the proposed scenario to see whether it would change the situation. If it doesn't change the situation, then that info wasn't helpful in evaluating the conclusion.

A) If land ur. is being rapidly depleted, what effect does that have on the economic viability of getting ur. from sea water? Hmm, well, if the amount of land ur. is rapidly going down, than the price is eventually going to go up. If the price goes up, what happens? Hey - that was a fundamental part of the original argument! The argument said that the current price (from land ur.) was lower than the sea ur. costs. But if that "current price" goes up, then it could go up enough to be higher than the sea ur. costs. That changes everything - now, sea ur. could be viable WITHOUT having to lower the sea ur. costs. There goes the author's cause-and-effect claim! What about the other way - land ur. is not being rapidly depleted? Well, in that case, nothing would change, and the author's claim is as valid as it was before. Okay - so this choice does actually give us two different scenarios, one in which the author's claim stays the same and one in which the author's claim doesn't look so good.

C) If there are advances that could reduce sea ur. extraction costs, what effect does that have on the economic viability of getting ur. from sea water? Hmm, well, if this is true then the costs could be lowered to the point that it becomes economically viable. If this happened, then the author's claim would be as valid as it was before. If there are NOT advances that could reduce sea ur. extraction costs, then what? Hmm. Then the author's claim would be as valid as it was before. So, either way, the answer to this question makes the author's claim as valid as it was before... that's not what we want. We want a choice that tells us: this way, claim looks okay, but that way, claim doesn't look okay. Eliminate.