Logical ReasoningDifficulty: Hard

PT1 S3 Q5 Explanation

To the Editor: In 1960, an astronomer

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

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Full official LSAT questions are available through LawHub. This page provides LSAT Lab's explanation, strategy, and review tools without republishing the full official question.

Stimulus

To the

In 1960, an astronomer proposed a mathematical model for determining whether extraterrestrial life exists. It was based on the assumptions that life as we know it could exist only on a planet and that many stars are, like our Sun, orbited by planets. On the basis that there are nine planets in astronomer’s model is wrong, and life as we know it exists only on the planet Earth.

Clay

What this question is testing

Weaken

Conclusion

Moltz is taking a strong position: the old astronomer's prediction was wrong, and life as we know it only exists on Earth.

Evidence

His main piece of evidence is one fact: nobody has detected a planet outside our solar system.

Evaluate

Watch this move carefully. Moltz is sliding from "we haven't detected any planets" to "there are no planets out there." That is a leap that only works if our detection equipment is good enough to actually find such planets.

Think about it this way: if you cannot find your keys in a dark room, that does not mean the keys are not there — it might just mean you need a flashlight. Same idea here. If telescopes are not yet sensitive enough to detect distant planets, the absence of detections proves nothing about whether the planets exist.

Goal

Find the answer that says, in effect, our current equipment is too weak to detect such planets even if they exist. That would force Moltz to reconsider.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
5.

Which one of the following, if accepted by Clay Moltz, would require him to

Answer choices

  1. Out of Scope17% picked this

    Forms of life other than life as we know it exist

    Moltz's conclusion is specifically about "life as we know it" — life of the type we're familiar with. This answer is about other forms of life, which Moltz explicitly excludes from his claim. Even if alien lifeforms exist, his narrow conclusion (no Earth-style life elsewhere) is unaffected.

  2. No Impact3% picked this

    There are many stars that are not orbited

    This actually pushes in the same direction as Moltz's view — fewer stars with planets means fewer potential homes for Earth-style life. The astronomer's model assumed many stars have planets; if many stars do not, the model's premise weakens, but Moltz's conclusion (the model is wrong, life is unique to Earth) is reinforced, not undermined.

  3. Correct68% picked this

    Detecting planets outside our solar system requires more sophisticated instruments than

    Why this is right

    This breaks Moltz's entire argument. He treated "no planets detected" as "no planets exist," but this answer says current detection instruments are too crude to find planets outside our solar system even if they are there. So the lack of detections proves nothing about whether such planets exist — and without that link, Moltz cannot conclude the astronomer's model is wrong, much less that life is unique to Earth. He would have to reconsider.

    Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.

  4. No Impact6% picked this

    The soundness of the conclusion reached by applying a mathematical model depends on the soundness of the assumptions on

    This is a general point about how mathematical models work. Moltz already takes this for granted — he is rejecting the astronomer's model precisely because he thinks one of its assumptions (many stars are orbited by planets) is unsupported by detection data. Endorsing the general principle "models depend on their assumptions" gives Moltz no new reason to reconsider his specific conclusion.

  5. No Impact6% picked this

    Due to sheer distances and expanses of space involved, any extraterrestrial civilization would have great

    Communication difficulty is irrelevant to whether extraterrestrial civilizations exist. Moltz's conclusion is about existence (no life outside Earth), not about whether we can talk to anyone out there. Even if civilizations cannot communicate with us, they could still be out there contradicting Moltz.

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