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Complete Question Explanation

Assumption. The correct answer choice is (A)

Assumptions are typically unspoken statements that the author must believe in order to believe that
argument. If the author’s belief in an assumption were rendered untenable, the argument would no
longer be believable. The argument here is that failure to preserve tropical rain forests will prevent
the development of important types of medicine. This belief is supported by evidence that many
types of medicine have come from substances only found in tropical rain forests and that many
similar substances in these rain forests remain undiscovered.

A further belief is required in order for the author to believe that important types of medicine would
go undiscovered if rain forests were destroyed. The author must believe that since past medicines
came in this manner, at least some future medicines could not come in any other way. Put differently,
if these medicines could be developed without discovering yet unknown substances in tropical
rain forests, then the author could not believe that preserving the rain forests was a necessary precondition
for the medicine’s development.

Answer choice (A): This is the correct answer choice. Discovery of unknown substances is
required for future development of medicine if our knowledge of current substances would not
lead to the same development. As with any Contender to an Assumption question, you can test this
answer by negating it and determining if it renders that argument unacceptable. This answer can be
negated as “there are no unknown substances of medicinal value that differ from substances already
discovered.” If the negation were true, then it would be unnecessary to preserve rain forests since
scientists could develop the same types of medicine by studying existing, known substances.

Answer choice (B): This answer would weaken the argument. If the author believed that most
substances from the rain forest were not unique to that environment, then it would be less necessary
to preserve the rainforest.

Answer choice (C): An assumption does not have to strengthen an argument. Many incorrect answers
on assumptions go beyond what is required for belief in the argument.

Here, for example, we are told that the majority of unique plant species contain substances of medicinal
value. Since there are so many unique plant species in the rain forest and most of them are likely to
have medicinal value, this would certainly support the importance of preserving the rain forest.

But that’s not the author’s argument; the author is arguing that developing important medicines
depends on preserving the rain forest. In order to believe that conclusion, the author does not have to
believe that the majority of plant species unique to the rain forest have medicinal value; the author
needs only believe that there are some unknown rain forest plants with medicinal value that cannot
be found any other way.

Answer choice (D): While it would be comforting to believe that scientists will extract the full
medicinal value of all substances they encounter in the rain forest, this belief is not required for
the argument. Even if scientists are woefully inefficient at discover the full range of medicinally
valuable substances in the rain forest, preserving the rain forest may still be the only way to make
certain medical discoveries. The arguments requires that certain discoveries can only come from
substance in tropical rain forests, regardless of whether scientists are able to make all such potential

Answer choice (E): This is a value statement. The author’s argument that some discoveries would
be precluded by the failure to preserve to rain forest does not depend upon any particular value
judgment. Whether or not is it desirable to preserve rain forests and make important medical
discoveries, the conditional relationship between the two would be unchanged. Thus, even if the
author were not in favor of preserving rain forests, he could still believe that medical developments
depended on doing so.
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Hi there PS,

On this question I stalled between A and D and chose D. Looking back I'm wondering if I misinterpreted D incorrectly.

I can't help but seem to interpret D as if it is saying that "scientists do in fact have the capability" to discover substances. Because obviously the capability to discover would be necessary or else what's the point in preserving them rain forests.

Now looking back and noticing "Any" - should I have partially taken this to mean "all that are present" will be discovered, in which case I could see how this isn't a necessary assumption, because really they only need to believe that "some" will/can be discovered if they preserved the rainforest ... maybe I need to go back and remind myself of what "any" really means on the lsat. :hmm:
 Lucas Moreau
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You are partially correct with regards to the "any" versus "some" distinction. You're right in that it isn't necessary that "any" - here meaning close to "each and every" - substance of medicinal value will eventually be discovered, that isn't a required assumption.

But look closely at the wording of D: It says any substance contained within species will be discovered if those species are studied. Not that each and every species containing substances of medicinal value indigenous to the rain forests will be discovered, but that every species of that description that is discovered and studied will yield its medicinal secrets.

You're still correct with regards to the fact that "some" would suffice, it's not necessary for "any" species to reveal its medicinal value if studied. But A is still the best answer, because if A is not true, then there is nothing novel to be found within the rain forest, and it does not follow that important medicine types will never be developed.

I hope this helps you understand a little better.
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What is the reason we eliminated answer choice E? Is it because it is not as strong as the language used in the stimulus?

 Adam Tyson
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The best reason to eliminate E is that it talks about what SHOULD be done - an opinion-based answer. Our stimulus has no opinions, just facts, so we should not be looking for an opinion-based assumption but a factual assumption - the author is assuming that something IS, not that something SHOULD BE. You wouldn't want an opinion as your answer unless you had an opinion as your conclusion.
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What is the main Diffrence between answer A and E
 Elizabeth Mulkey
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Hi Kappe,

This is an Assumption question, so we're looking for what needs to be true for this argument to be true. If we're just comparing answer choice (E) and answer choice (A), the biggest difference is that answer choice (E) is phrased in opinion language ("The tropical rain forests should be preserved..."), but choice (A) is stated factually. The stimulus is an argument based on fact statements, not opinions, so the answer choice we're looking for should also be a factual statement.

Hope this clarifies things!

- Elizabeth
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Is D wrong because it's too extreme by saying "any"? Would the answer choice be correct if it said "some substances of medicinal value will be discovered.." because the opposite, which would say "no substances of medicinal value will be discovered" wrecks the argument? If no scientist can find the substances with medicinal value then they can't develop important medicine.

Thank you
 Clay Cooper
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Hi Lsat2016,

Thanks for your question.

Answer choice D is incorrect, not because of fine distinctions in its language, but because it is not necessary to prove the conclusion. Note that our conclusion doesn't make any claim about what will happen if the rainforest is preserved. Instead, the conclusion claims only that if the rainforest is NOT preserved, important medicines will be lost.

Therefore, any claim about what would happen if the rainforest is preserved and scientists are allowed to study plant species within it (like D) is irrelevant to our conclusion.

You mention the negation technique, but it only confirms that D is correct. The negated form of D is "It is not the case that any substance of medicinal value contained in plant species indigenous to tropical rain forests will eventually be discovered if those species are studied by scientists." In other words, medicinally valuable substances may escape discovery even if the rainforest is preserved.

However, this does not wreck the argument, or in fact have any impact on the conclusion at all. Our conclusion is about what will happen if the rainforest is destroyed - and nothing more. The author makes no claims about what might happen if the rainforest is not destroyed.

I hope that helps.
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Is "should" always used to point at a value statement? I went for E, as I read should = ought to. I thought A was wrong because new types of medicine might not require necessarily different substant, but probably larger amounts of already discovered substances. Thanks in advance.

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