QUESTION TEXT: Many important types of medicine have been …
QUESTION TYPE: Necessary Assumption
CONCLUSION: We won’t develop certain important medicines unless we protect tropical rain forests.
REASONING: Some medicine has been made from substances found only in tropical rain forests. There are lots of plant species scientists haven’t looked at, and some of them probably have medically important substances.
ANALYSIS: This sounds like a pretty good argument. But the author ignores a possibility: maybe the substances in the unexamined plants are the same medically valuable substances we’ve already found in other plants.
___________
- CORRECT. If this isn’t true the argument fails.
Negation: There are no new medically useful substances in the plants we haven’t studied. The substances are the same as those already found in other plants. - If this is true it weakens the argument. The author emphasized that some important plants only grow in the tropics.
- This seems tempting, because it strengthens the argument. But an answer isn’t right just because it strengthens the argument. The answer has to be necessary. “Most” statements are almost never necessary, because the negation moves us from 51% to 50% (i.e. “not most”). An insignificant change in almost all cases.
Negation: Only 50% of plants studied had medically important substances. - This doesn’t have to be true. This answer would be right if it had said “At least some substances of medical value will eventually be discovered if scientists study the unexamined plants.”
It isn’t necessary that scientists discover all the substances. We only need to know that they would discover some of the substances. - This answer talks about what we should do. The stimulus was only about what is true. On the LSAT, there is zero overlap between what should be true and what is true. So this answer is talking about the wrong thing.
This answer feels like it’s true but that’s not what we’re looking for. We’re looking for a necessary assumption.
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MemberPeng Han says
Hi! I cannot figure out why A is the correct answer though I get to it through process of elimination. I use a diagram to understand the argument. (Note that although I realize the original statements are not rigid formal logic, but I dichotomized “important types medicine” into those that have been developed from rain forest plants and those that have not been developed, and “tropical rain forest plants” into those that have been studied and unstudied in order to simplify my understanding.)
Reasoning: M (developed) –> P (studied) –> RF
P’ (unstudied) –> RF
P’ (unstudied) likely contain M’ (undeveloped)
Conclusion: Not RF –> Not M’ (undeveloped)
There is a gap b/w the conclusion and reasoning that we can fill by:
M’ (undeveloped) –> P’ (unstudied)
Meaning those important types of medicines that have not been developed are contained only in tropical rain forest plants that are not yet studied. And I notice this is both a necessary and sufficient condition. The conclusion “never” is extreme, so we probably will have an extreme assumption.
However, I am not sure why we have to assume that some undeveloped types of medicine has to be different from the developed ones. If we negate this, then we have undeveloped ones and developed ones are of same medicine value. How would it wreck the argument? We might still have other sources for important medicine except for the rain forests.
For A to be a correct necessary assumption, I think the conclusion should be like: If the tropical rain forests are preserved, important types of medicine will be developed. I.e., the negation of the original statement.
TutorLucas (LSAT Hacks) says
I think one of the primary issues here is your use of conditional reasoning diagrams when you’re being presented with statements that don’t use conditional reasoning. These sorts of diagrams can save time when dealing with the rights kinds of statements. But, when dealing with statements that don’t use conditional reasoning, you can over-complicate things that could be done much more simply.
This answer choice can actually be arrived at quite easily. If there are no new medically useful plants, then how can this conclusion hold true?
In future, I’d recommend:
(1) Not using conditional reasoning diagrams when presented with statements that don’t use conditional reasoning
(2) Trying a new approach if you’ve noticed you’ve sunk your time into a complicated set of diagrams/reasoning but still haven’t arrived at the answer
MemberPeng Han says
Hi Lucas! Thanks for the suggestion. I did not use the diagram while doing the test. I diagrammed it trying to explain the reasoning in another way.
I used negation test on A. I don’t know why the conclusion cannot follow. I still have the concerns as expressed in the last two paragraphs in my last post.
TutorLucas (LSAT Hacks) says
We can make the common sense assumption here (from wording and context) that the conclusion is actually saying: “other important types of medicine will never be developed.” Or, rather, we could say that the assumption is that the important types of medicine in the conclusion are those derived from plants that have not yet been studied by scientists.
So, when we negate (A), we get: “there are not substances of medicinal value contained in tropical rain forest plants not yet studied by scientists that differ from those substances already discovered in tropical rain forest plants.” When we plug this back into the argument, it’s clear that the argument falls apart because the rain forest doesn’t provide other important medicines.