Logical ReasoningDifficulty: Easy

PT2 S4 Q18 Explanation

Some cleaning fluids

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

TopicsMust be True

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Full official LSAT questions are available through LawHub. This page provides LSAT Lab's explanation, strategy, and review tools without republishing the full official question.

Stimulus

Some cleaning fluids, synthetic carpets, wall paneling, and other products release toxins, such as formaldehyde and benzene, into the household air supply. This is not a problem in well-ventilated houses, but it is a problem in houses that are so well insulated that they trap toxins as well as heat. Recent tests, one test, 20 large plants eliminated formaldehyde from a small, well-insulated house.

Assume that a person who lives in a small, well-insulated house that contains toxin-releasing products places houseplants, such in the house.

What this question is testing

Must be True

Premise

The stimulus says houseplants remove some household toxins. The one specific test mentioned: 20 plants eliminated formaldehyde from a small, well-insulated house.

Evaluate

So what do we actually know? We know formaldehyde was successfully removed in the test. We do not know whether benzene was removed — the stimulus mentions benzene as a household toxin but never says plants handle benzene. The phrase "some toxins" leaves room for plants to fail at others.

Must Be True is strict: the answer must be guaranteed by the stimulus. We cannot make broad claims like "the air is safe" or "all toxins decrease." We can only say what the stimulus directly supports — which, specifically, is that plants reduce formaldehyde.

Goal

Find the answer that says only what the formaldehyde test guarantees: if formaldehyde is in the air, its level will decrease.

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

The question
18.

Which one of the following can be expected as

Answer choices

  1. Too Strong1% picked this

    There will no longer be any need to ventilate

    The stimulus never says plants remove enough toxins to eliminate the need for ventilation. Plants remove "some" household toxins; well-insulated houses still have toxin-releasing products (cleaning fluids, paneling, etc.); and the formaldehyde test only addresses one toxin. Saying ventilation is no longer necessary goes far beyond what the stimulus supports.

  2. Contradicted2% picked this

    The concentration of toxins in the household air supply will remain

    The stimulus directly tells us plants remove some toxins, and 20 plants eliminated formaldehyde in the test. So toxin concentrations are not going to remain the same — at minimum, formaldehyde will decrease. This contradicts the stimulus.

  3. Too Strong6% picked this

    The house will be warm and have a safe

    "Safe air supply" overshoots. The stimulus only supports that plants remove some toxins — and the test specifically showed only formaldehyde elimination. Benzene and any other untested toxins might still pose a danger. We cannot conclude the air is safe.

  4. Correct83% picked this

    If there is formaldehyde in the household air supply, its level

    Why this is right

    This is the modest inference the stimulus actually supports. The test showed 20 plants eliminating formaldehyde in a small, well-insulated house — which is precisely the setup the question describes. So if formaldehyde is in the air, plants will reduce it. The conditional ("if there is formaldehyde") and the modest claim ("its level will decrease") match exactly what the stimulus guarantees.

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

  5. Term Shift9% picked this

    If formaldehyde and benzene are being released into the household air supply, the quantities released

    This talks about the quantities released decreasing. But plants do not affect the rate at which products release toxins — plants pull toxins out of the air after release. The stimulus is about removing toxins from the air supply, not slowing the source. This shifts what plants are claimed to do.

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