Logical ReasoningDifficulty: Hard

PT128 S3 Q20 Explanation

Professor Gandolf says that all

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

TopicsNecessary Assumption

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Stimulus

Professor Gandolf says that all political systems that aim at preventing conflict are legitimate. However, totalitarian political systems are usually good at preventing conflict, since those who are not in power are subject to the will of the powerful. illegitimate, Professor Gandolf's principle must be false.

What this question is testing

Necessary Assumption

Your task

Find the assumption the argument requires in order for its conclusion to hold.

Common trap

Answers that would help the argument but aren't strictly required (sufficient, not necessary).

Winning move

Negate each choice — the right one breaks the argument when negated.

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

The question
20.

Which one of the following is an assumption required by

Answer choices

  1. Out of Scope: legitimate Illegal Opposite5% picked this

    At least one political system that does not aim at preventing

    The author's only objectives in this argument are to establish that there is an example of a political system that "aims to prevent conflict" and "is not legitimate". Thus, she doesn't need to assume that any governments anywhere are legitimate. If they were all illegitimate it could only help her argument. This is just doing the ol' Illegal Lightswitch on what the author is assuming. AUTHOR at least one pol sys that does aim is not legit ANSWER at least one pol sys that does not aim is legit

  2. Weakens18% picked this

    If a totalitarian political system prevents conflict, such prevention is only incidental to

    This perfectly sums up how we would object to the argument, not what the argument is assuming. The author assumes that because totalitarian systems succeed in preventing conflict, they must aim to do so. Our objection could be that "maybe they succeed in preventing conflict, but it's just a random byproduct of what they're actually aiming to do".

  3. Correct67% picked this

    At least one totalitarian political system aims at

    Why this is right

    If we negated this, it would say, "ZERO totalitarian political systems aim at preventing conflict". That would destroy the author's argument. In order to refute Professor G's principle, she must establish 1. pol sys X aims to prevent conflict 2. pol sys X is not legitimate Since the author is trying to use "totalitarian systems" as her way of doing this, if it turns out that zero of them are #1, then her argument is hopeless.

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

  4. Too Strong5% picked this

    No political system that fails to prevent conflict

    This sets up a very powerful conditional idea: political system fails ? not legitimate to prevent conflict She hasn't set out to prove that all political systems of a certain type are illegitimate. She is only trying to prove that Professor G's principle is wrong. She's resisting his idea that all political systems of a certain type are legitimate. So she's only on the hook for assuming that at least one type of government is sometimes not legitimate.

  5. Out of Scope: not totalitarian4% picked this

    Some political systems that are not totalitarian

    She only talks about totalitarian political systems, so we can't say she's committed herself to assuming anything about non-totalitarian systems.

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