Logical ReasoningDifficulty: Medium

PT124 S3 Q20 Explanation

The ability of mammals

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

TopicsNecessary Assumption

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Stimulus

The ability of mammals to control their internal body temperatures is a factor in the development of their brains and intelligence. This can be seen from the following facts: the brain is a chemical machine, all chemical reactions are temperature dependent, and any organism that these reactions occur at the proper temperatures.

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 on which the

Answer choices

  1. Too Strong4% picked this

    Organisms unable to control their body temperatures do not have the capacity to generate internal body heat without

    That an animal controls its body temperature through internal factors is not required of the argument since external factors would work just the same.

  2. Out of Scope1% picked this

    Mammals are the only animals that have the ability to control their

    What is true for animals other than mammals is not relevant to the argument.

  3. Negation14% picked this

    The brain cannot support intelligence if the chemical reactions within it are subject

    This negates the argument’s conclusion.

  4. Correct77% picked this

    The development of intelligence in mammals is not independent of the chemical reactions in their brains taking place

    Why this is right

    This rules out the possibility that the development of intelligence is not related to the chemical reactions the evidence implies depend on occurring at proper temperatures.

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

  5. Negation4% picked this

    Organisms incapable of controlling their internal body temperatures are subject to

    This negates a premise of the argument.

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