PT143 · S4 · Q20 Many important types of medicine

This is actually one of our objections, not something the author would assume (authors don't assume things that hurt their arguments). A correct answer could have sounded like this: at least some of the tropical rain forest plants that have yet to be studied and that contain substances of medicinal value cannot be found growing in other types of environment.

The word / concept of "most" is wrong on Necessary Assumption 99% of the time we see it. After all, when you negate "most", you basically go from thinking something is true 51% of the time to thinking it's true 49% of the time. Would it matter to the author's argument whether 51% of unique tropical rain forest plants have turned out to have cool medicinal substances vs. only 49% of them? Of course not. Either way, that's a sizable, meaningful chunk of them that have medicinal value! Because the difference between 51% and 49% is almost always meaningless, authors almost never need to assume that something is true of "most".

This answer accuses the author of thinking, "if the scientists were able to get their hands on these thousands of unstudied plants, in 100% of cases where one of these plants had something medicinally useful, scientists would discover it." Was the author thinking that scientists would have a perfect success ratio when it comes to spotting a medicinally valuable substance? Would the argument be hurt if they were only 99% successful at finding new plants that had medicinal substances? Of course not. If they're even 1% successful at finding a new substance, and that goes on to become an important medicine, then the author's argument will have been correct.

This argument was descriptive, not normative, so language like "should" is just brand new. This is a classic piece of bait LSAT uses on things like Necessary Assumption or Main Conclusion. We're only supposed to be attending to what was actually said, but they're trying to entice us into picking the Next Thing that the author might say. We can only look at the internal logic of the statements. We're not supposed to be psychoanalyzing these authors and thinking, "Why would you even be saying the things you're saying? You must be hoping to ultimately go here with the conversation". I could make an argument about "President Nancy is eroding democratic norms. Thus, if she is re-elected, this country will no longer be a democracy". Am I assuming that "President Nancy shouldn't be re-elected"? Nope. Because you have no idea whether I actually want to keep this country a democracy. Similarly, we have no idea if this author wants important new medicines to be developed. Not to mention, we're only hearing part of the story. Maybe President Nancy will end democracy, but she'll also end poverty and systemic racism. Maybe I'd accept those tradeoffs. Similarly, maybe getting rid of the rain forests would make us miss out on some important types of medicine, but it would make my family's logging company rich! Maybe I'd accept those tradeoffs.