#25 - Almost all microbe species live together in dense

[Administrator]

Complete Question Explanation

Justify the Conclusion. The correct answer choice is (C)

This argument can be broken down in the following manner:

• Premise: All microbe species live together in dense, independent communities
  
  Premise/Sub. Conclusion: Scientists cannot cultivate them in isolation
  
  Main Conclusion: Scientists lack complete knowledge of most microbe species

In short, because it is impossible to cultivate any one microbe species in isolation, the author concludes that microbiologists lack complete knowledge of most microbe species. Notice that this simple argument requires you to pay little attention to the wordy first sentence of the stimulus: often times, the trick to answering Justify the Conclusion questions quickly and efficiently is to focus only on the relationship between the premise that directly support the conclusion. The first premise only functions as a premise for the second; chances are, it will be irrelevant to proving the conclusion.

Just because we cannot cultivate any one microbe species in isolation does not necessarily mean that we cannot have complete knowledge of them. To justify the conclusion, the author needs to establish that cultivating microbe species in isolation is necessary for having complete knowledge of them. Answer choice (C) is therefore correct.

Answer choice (A): While this answer choice can be inferred from the premises in this argument, our job is to prove the conclusion, not answer a Must Be True question. Since it is impossible to prove a conclusion by supplementing a premise with its logical equivalent, this answer choice is incorrect.

Answer choice (B): This answer choice is tricky: while it does provide a link between the first two parts of this argument, it only justifies the subsidiary conclusion and not the main one. This answer choice is incorrect.

Answer choice (C): This is the correct answer choice. If no microbiologist can have complete knowledge of any species of organism unless that microbiologist can cultivate that species in isolation, then cultivating species in isolation is a necessary condition for having complete knowledge of the species:

• Complete knowledge of a species → Cultivate species in isolation

Notice the strong language used in this answer choice ("any species"): this is a common feature of correct answers in Justify the Conclusion questions, as their goal is to definitively prove the conclusion. Answer choice (C) would be a terrible answer to an Assumption question, which would only presuppose that complete knowledge of microbe species (not any species in general) requires our ability to cultivate them in isolation.

Answer choice (D): While this answer choice can be inferred from the information provided in the stimulus, our job is to prove the conclusion, not answer a Must Be True question. Since it is impossible to prove a conclusion by supplementing a premise with its logical equivalent, this answer choice is incorrect. Remember: proving a conclusion always requires the introduction of a new element into the structure of the argument.

Answer choice (E): While this answer choice can be inferred from the author's conclusion, our job is to prove the conclusion, not analyze what follows from it. This answer choice is incorrect.

[mariahenain]

Is answer choice C also correct because, according to the Justify Formula, microbiologists is a "rogue" term as it is not mentioned in the premises?

[Adam Tyson]

I'd agree with that analysis, Maria! However, we could have as easily accepted an answer that was broader and included microbiologists without specifically naming them. For example, "nobody can have complete knowledge of any species of organism unless they can cultivate that species in isolation" or "it is impossible to have complete knowledge of anything unless that thing can be studied in isolation." In Justify questions, we can sometimes go bigger than we need to. Other times, however we cannot, as when the stem asks us "which of the following is required in order to justify the conclusion". Then we should not go any bigger than the minimum amount of justification required, because any more is not required to justify. When that happens, we tend to treat those questions as Assumption questions rather than Justify the Conclusion, although there is a case to be made that they are a type of Justify the Conclusion with a restriction on the amount of justification.

This test is very flexible, and there aren't that many absolutes along the way. Getting a good grounding in the basic question types will eventually lead to an even broader understanding and approach wherein we can move away from being entirely mechanical and worrying about what label to apply to the question stem and instead just focus on what the stem is asking of us.

Keep at it!

[LSAT2018]

I selected Answer (C) as the answer but would like to clarify some things.
In the stimulus, it says 'For this reason, it is currently impossible to cultivate any one such species in isolation. Thus, microbiologists lack complete knowledge of most microbe species.'

Then the correct answer proceeds in the form of conditional reasoning,' No microbiologist can have complete knowledge of any species of organism unless that microbiologist can cultivate that species in isolation.'
I get that this is a contrapositive but I would like to ask how complete knowledge of most microbe species changes to complete knowledge of any species.

[Claire Horan]

Hi LSAT2018,

Kudos to you for being worried about the language differing. Although it isn't a problem here, as I will explain next, it's such an important thing to pay attention to. And now to answer your question.

Don't lose sight of the question stem, what the question is asking you to do. The question stem is "Which one of the following, if assumed, enables the argument’s conclusion to be properly drawn?" So that means if an answer choice allows for a valid argument, it is correct. It does not have to be the only or least-restrictive statement possible; in other words, there may be other possible statements that would also justify the conclusion, but only one such statement is part of the five answer choices.

Here, from combining premises 1 and 2, we know that it is "currently impossible to cultivate in isolation "almost all microbe species." (If you are confused about this combination, see the word "such" in premise 2? That shows the sentence refers to the microbes identified in premise 1, which live in dense communities.) The conclusion is that "microbiologists lack complete knowledge of most microbe species." This conclusion is justified if C, it is impossible to have complete knowledge of a species without cultivating it in isolation.

Good luck studying!