Logical ReasoningDifficulty: Hard

PT6 S3 Q15 Explanation

Twenty years ago the Republic

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

TopicsNecessary Assumption

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Stimulus

Twenty years ago the Republic of Rosinia produced nearly 100 million tons of potatoes, but last year the harvest barely reached 60 million tons. Agricultural researchers, who have failed to develop new higher-yielding strains of potatoes, are to blame for this decrease, since research and not with the needs of Rosinia.

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
15.

Which one of the following is an assumption on which the

Answer choices

  1. Too Strong: any / futile10% picked this

    Any current attempts by agricultural researchers to develop higher-yielding potato strains

    We're trying to prove that the ag researchers are at fault for the decreased harvest over the last 20 years. Whatever they're currently attempting isn't relevant, because we're trying to explain what happened over a different time frame. "Any" and "futile" are also big red flags.

  2. Correct65% picked this

    Strains of potatoes most commonly grown in Rosinia could not have produced the yields last year

    Why this is right

    We love "ruling out" language on Necessary Assumption questions because it typically indicates a defender assumption. This answer rules out the possibility that we could have matched the old harvest with the existing strains, which defends against the objection we came up with in our stimulus evaluation. If you didn't make this prediction, you could test this answer by negating it. If the existing strains could have produced the yields they once did, then why are we blaming the ag researchers? The argument crumbles if this answer isn't true, which tells us for sure that it's correct.

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

  3. Out of Scope:7% picked this

    Agricultural researchers often find concrete solutions to practical problems when investigating

    Basically everything in this answer is out of scope: concrete solutions, practical problems, seemingly unrelated questions. There's no reason our argument would hinge on assuming anything about these concepts.

  4. Weakener (if anything)13% picked this

    Wide fluctuations in the size of the potato crop over a twenty-year period

    If anything, this weakens the argument by providing an alternative causal difference maker, albeit a pretty lame one. "Hey, stuff happens! Potato harvests just fluctuate."

  5. Out of Scope: funding4% picked this

    Agricultural research in Rosinia is funded by

    We don't need to assume anything about funding in order to conclude that the blame lies with the ag researchers.

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