Logical Reasoning

PT105 · S4 · Q5 The most reliable way to

A free, expert breakdown of this official LSAT Logical Reasoning question.

Save & drill this skill — build targeted practice sets from questions like this one
Video walkthroughs — watch every question solved step by step
81 official LSATs — as questions, timed sections & full-length tests

The most reliable way to detect the presence of life on a planet would be by determining whether or not its atmosphere contains methane.

Conclusion

The most reliable way to detect the presence of life on a planet would be to ascertain whether its atmosphere contains methane.

Evidence

If methane isn't constantly Methane replenished by the biological → disappears processes of living beings

Evaluate

When an author argues that, "the best way to achieve X is Y", there will be two big assumptions we could attack - the author assumes that Y is a viable way to achieve X - the author assumes that there isn't some other way of achieving X that is even better than Y

It will be hard for us here to argue that . By contrapositive logic, the rule that this author has given us says that .

So we can't really argue with the author by saying, . The best we could do is say, .

The other avenue we have is to argue that some other way of detecting the presence of life is even more reliable. (maybe receiving radio communications?)

Goal

Look for an answer that suggests that the methane method isn't super reliable (i.e. we might detect methane in the atmosphere even though the planet does not have living beings present), or an answer that suggests that there might be a more reliable way of detecting life than the methane way.

Which one of the following statements, if true, most seriously weakens the argument?

There are other ways of
No Impact
Cool, but are these other ways more reliable than the methane-detection method? Unless the answer is suggesting that, it isn't really doing anything. We already know there's more than one way to detect the presence of life because the author is referring to methane-detection as "the most reliable way". The use of a superlative like "most" implies that there are at least three ways. So this answer is actually adding nothing we didn't already know.
6% picked this
Correct
Not all living beings have
Why this is right
The author's statements establish that "IF we see methane, we know there's life there" (because it needs to be constantly replenished by living beings). But what if we don't see methane? Does that mean there isn't life on a planet? We're not sure. According to this answer, we wouldn't be able to tell whether there's life on a planet that doesn't have methane, because it's possible to have life without methane. A lot of LSAT arguments that deal with using a certain type of test / measurement / metric / method are ultimately testing the ideas of False Positives and False Negatives. To judge the soundness / accuracy of a method of measurement, you want to consider its rate of false positives and its rate of false negatives. With the methane method, it sounds like we'd almost never have a false positive (where there WAS methane but WASN'T life). But, according to this answer, the methane method might lead to a lot of false negatives (where there ISN'T methane but there IS life). The methane method has no way to detect the presence of non-methane-producing life, so it doesn't sound like "the most reliable" way to detect the presence of life. In the vocabulary of the initial explanation, this is targeting the assumption that "the methane-method is a viable way to test for the detection of life". It wouldn't be a viable way of testing for life that doesn't emit methane.
Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.
72% picked this
We are incapable at present
Out of Scope: capable of detection
The author's conclusion is about "most reliable" method, not the most currently usable or currently practical method. If you were working for a "get out the vote" campaign, you might say, "The most reliable way to get someone to vote would be to knock on everyone's door, come into their living room, and chat about the issues for a few minutes." Someone else can say, "Our organization is presently incapable of knocking on every voters door and coming inside to chat with them", but that doesn't undermine the idea that knocking on every door would be the most reliable way.
15% picked this
Some living beings biologically produce
Too Weak
Answer with "some / sometimes / can / not all" are almost always wrong on Strengthen, Weaken, and Paradox. (not always wrong, though, as this correct answer shows) It has no effect to say, "There's at least one living being that only produces a li'l methane." Cool. That doesn't change the reality that "if we see methane, we'll know that there are biological being constantly replenishing it".
2% picked this
Earth is the only planet
No Impact
This is just about which planets are known to contain methane. There may be billions of planets that do contain methane but they're too far away for us to take a remote chemical reading on the atmosphere. Our author's argument can be true in a hypothetical way. She isn't saying that we're going to start using this method, or that we have used it, or that we should use it. She's only concluding that, "in theory, this is the most reliable way".
6% picked this

Continue the review in LSAT Lab

Save this question, watch the video walkthrough, and drill similar questions in your LSAT Lab account.

Save and practice this skill

LSAT Lab

Turn this review into a targeted study plan.

Save this question, drill more like it, watch the video walkthrough, and track your progress in your LSAT Lab account.

Start practicing free