Logical ReasoningDifficulty: Medium

PT109 S4 Q5 Explanation

Astronaut: Any moon, by definition,

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

TopicsSufficient Assumption

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Stimulus

Astronaut: Any moon, by definition, orbits some planet in a solar system. So, the moons in solar system the planet Alpha.

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
5.

The astronaut’s conclusion follows logically if which one of the following

Answer choices

  1. Nothing About 'Alpha'0% picked this

    There is only one moon in

    The fact that there's only one moon in S4 doesn't prove that it orbits Alpha. Maybe it orbits Beta, or any other planet in S4.

  2. Nothing About 'Alpha'15% picked this

    Every moon in S4 orbits the

    The fact that all the moons orbit the same planet doesn't prove that they all orbit Alpha. Maybe they all orbit Beta, or any other planet in S4.

  3. Correct78% picked this

    Alpha is the only planet in

    Why this is right

    If Alpha is the only planet in solar system S4, and all moons have to orbit some planet in a solar system, then all the moons in solar system S4 must orbit Alpha (it's their only option!)

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

  4. Nothing About 'Alpha'1% picked this

    Every planet in S4 is orbited by more than

    The fact that every planet in S4 has multiple moons doesn't give us any way to prove that all the moons in S4 orbit the same planet, and we'd have no idea whether that planet is Alpha.

  5. Too Weak6% picked this

    There is at least one moon that

    This doesn't prove that all the moons in S4 orbit Alpha; it only establishes that at least one moon in S4 orbits Alpha.

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