Logical ReasoningDifficulty: Hard

PT129 S3 Q20 Explanation

Ethicist: Every moral action

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

TopicsParallel

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Stimulus

Ethicist: Every moral action is the keeping of an agreement, and keeping an agreement is nothing more than an act of securing mutual benefit. Clearly, however, not all instances of agreement-keeping are moral mutual benefit are not moral actions.

What this question is testing

Parallel

Your task

Break the argument into its conclusion and evidence, then do exactly what the question stem asks with that structure.

Common trap

Answers that sound relevant to the topic but don't connect to the argument's actual reasoning.

Winning move

Predict what a right answer must do, then test each choice against the conclusion-evidence gap.

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.

The pattern of reasoning in which one of the following arguments is most similar to that in

Answer choices

  1. Wrong Validity12% picked this

    All calculators are kinds of computers, and all computers are devices for automated reasoning. However, not all devices for automated reasoning are calculators. Therefore,

    All calculators are kinds CAL → COM of All computers are COM → DEV devices for automated reasoning. However, not all DEV ↢some↣ ~CAL devices for automated reasoning are Therefore, some DEV ↢some↣ ~COM devices for automated reasoning are not computers. The conclusion is not a valid inference of the premises. It is however a common, and invalid, inference drawn from the second premise.

  2. Wrong Validity9% picked this

    All exercise is beneficial, and all things that are beneficial promote health. However, not all things that are beneficial are forms of exercise. Therefore,

    All exercise is beneficial. E → B All things that are B → PH beneficial promote health. However, not all things B ↢some↣ ~E that are beneficial are forms of exercise. Therefore, some E ↢some↣ ~PH exercise does not promote health. This conclusion negates the inference that could be drawn from the second and third premises.

  3. Wrong Structure2% picked this

    All metaphors are comparisons, and not all comparisons are surprising. However, all metaphors are surprising. Therefore, some

    All metaphors are M → C comparisons. Not all comparisons C ↢some↣ ~S are surprising. However, all metaphors M → S are surprising. Therefore, some C ↢some↣ ~M comparisons are not metaphors. While the conclusion does follow from the second and third premises, the logical structure of this argument does not parallel the stimulus because for several reasons. The two “if/then” statements cannot be combined in this answer. Furthermore, for the “some” statement to match the stimulus it should say that not all comparisons are metaphors.

  4. Wrong Validity8% picked this

    All architecture is design and all design is art. However, not all design is architecture. Therefore, some

    All architecture is design. ARC → D All design is art. However, not all design is D → ART architecture. Therefore, some art is not D ↢some↣ ~ARC design. The conclusion is not a valid inference of the premises. It is however a common, and invalid, inference drawn from the second premise.

  5. Correct68% picked this

    All books are texts, and all texts are documents. However, not all texts are books. Therefore, some

    Why this is right

    All books are texts. B → T All texts are T → D documents. However, not all texts T ↢some↣ ~B are books. Therefore, some D ↢some↣ ~B documents are not books. The conclusion follows logically from the second and third premises.

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

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