Logical ReasoningDifficulty: Medium

PT123 S3 Q11 Explanation

Feathers recently taken from seabirds

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

TopicsNecessary Assumption

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Stimulus

Feathers recently taken from seabirds stuffed and preserved in the 1880s have been found to contain only half as much mercury as feathers recently taken from living birds of the same species. Since mercury that accumulates in a seabird’s feathers as the feathers grow is derived from fish eaten by the fish are higher now than they were 100 years ago.

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
11.

The argument depends on assuming

Answer choices

  1. Weakens10% picked this

    the proportion of a seabird’s diet consisting of fish was not as high, on average, in the 1880s

    This weakens the argument by providing an alternative explanation for the difference in the amount of mercury contained in the seabirds’ feathers.

  2. Irrelevant Relationship6% picked this

    the amount of mercury in a saltwater fish depends on the amount of pollution in the ocean

    Connecting mercury and pollution has no impact on the argument.

  3. Irrelevant Relationship3% picked this

    mercury derived from fish is essential for the normal growth of

    Whether mercury is helpful or not is not relevant to why the two samples contained different levels of mercury.

  4. Weakens2% picked this

    the stuffed seabirds whose feathers were tested for mercury were not

    This weakens the argument by providing an alternative explanation for the difference in the amount of mercury contained in the seabirds’

  5. Correct80% picked this

    the process used to preserve birds in the 1880s did not substantially decrease the amount of mercury

    Why this is right

    This defends the argument from the alternative explanation for the difference in the amount of mercury contained in the seabirds’ feathers.

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

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