Logical ReasoningDifficulty: Hard

PT132 S4 Q18 Explanation

If there are sentient beings

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

TopicsSufficient Assumption

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Stimulus

If there are sentient beings on planets outside our solar system, we will not be able to determine this anytime in the near future unless some of these beings are at least as intelligent as humans. We will not be able to send spacecraft to planets outside our solar system anytime in near future would have to be at least as intelligent as we are.

What this question is testing

Sufficient Assumption

Your task

Find the assumption that, if added, guarantees the conclusion follows.

Common trap

Answers that only partly bridge the gap, leaving the conclusion unproven.

Winning move

Identify the new term in the conclusion and pick the choice that links it to the evidence.

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

The question
18.

The argument's conclusion can be properly inferred if which one of the

Answer choices

  1. Out of Scope - Opposite Group2% picked this

    There are no sentient beings on planets in our solar system other than

    The issue is whether we can detect sentient beings outside our solar system, not within.

  2. Out of Scope: want to communicate19% picked this

    Any beings that are at least as intelligent as humans would want to communicate with sentient beings outside

    Whether communication is desired with sentient beings outside our solar system is irrelevant to the argument.

  3. Premise Support7% picked this

    If there is a sentient being on another planet that is as intelligent as humans are, we will not be able to send spacecraft

    This supports the first premise, but not the argument about detecting a sentient being outside our solar system.

  4. Correct45% picked this

    If a sentient being on another planet cannot communicate with us, then the only way to detect its existence is by sending

    Why this is right

    This answer convinces us that the only two ways to detect sentient beings outside the solar system are for us to send a spacecraft or to have them communicate with us. We could write this answer as a conditional that says, "If we can't send a spacecraft, then the only way to detect such beings is for them to communicate with us". The author's evidence established that we can't send a spacecraft anytime soon. So combining that idea with this answer, we know that "The only way to detect such beings anytime soon is for them to communicate with us". And the second premise says that "for them to communicate with us, they'd need to be at least as intelligent." So we can combine those two ideas to derive the conclusion: "The only way to detect such beings anytime soon is for them to be at least as intelligent as us".

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

  5. Reversed Premise27% picked this

    Any sentient beings on planets outside our solar system that are at least as intelligent as humans would be

    This is just a conditional logic reversal of the second premise.

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