Logical ReasoningDifficulty: Hard

PT11 S2 Q25 Explanation

The fact that tobacco smoke

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

TopicsParallel

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Stimulus

The fact that tobacco smoke inhaled by smokers harms the smokers does not prove that the much smaller amount of tobacco smoke inhaled by nonsmokers who share living space with smokers harms the nonsmokers to some degree. Many substances, large quantities but beneficial in small quantities.

What this question is testing

Parallel

Pattern

The argument has three pieces:

1. Large amount of something causes harm.

2. That doesn't prove a smaller amount causes a smaller harm.

3. Counter-example: another substance where large amounts are harmful but small amounts are beneficial (a complete reversal, not just "less harmful").

The vitamin A example is doing the heavy lifting — it shows the dose-response relationship can flip, not just dampen.

Goal

Find an answer with this exact three-piece structure: large amount bad, denial that small amount is bad, supporting example where small amounts are positively beneficial.

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

The question
25.

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

Answer choices

  1. Bad Match17% picked this

    The fact that a large concentration of bleach will make fabric very white does not prove that a small concentration of bleach will make

    This argument lacks the key reversal. The supporting example says a small amount of bleach has effects "too slight to change the color of the fabric" — i.e., a smaller version of the same effect, not a beneficial reversal. The original used vitamin A as a substance where small amounts flip from harm to benefit. Without the flip, this is a different pattern.

  2. Bad Match7% picked this

    Although a healthful diet should include a certain amount of fiber, it does not follow that a diet that includes large amounts of fiber

    This argues that more isn't always better — a different shape. The original concluded that less doesn't necessarily preserve the same effect. This goes the other way: questioning whether more is healthier rather than whether less is harmful. Wrong direction.

  3. Bad Match6% picked this

    The fact that large amounts of chemical fertilizers can kill plants does not prove that chemical fertilizers are generally harmful to plants. It proves

    This concludes that fertilizers aren't generally harmful — a sweeping defense of the substance. The original concludes only that small amounts might not be harmful (without claiming the substance is generally fine). The conclusions are at different strengths.

  4. Bad Match8% picked this

    From the fact that five professional taste testers found a new cereal product tasty, it does not follow that everyone will like it. Many

    This argues from some people's positive reaction that not everyone will react the same way — a generalization-from-sample issue. The original is about dose-response (large vs. small amounts), not about variation among people. Different pattern.

  5. Correct62% picked this

    Although watching television for half of every day would be a waste of time, watching television briefly every day is not necessarily even a

    Why this is right

    This matches all three pieces. (1) Large amount of TV (half the day) = bad (a waste). (2) That doesn't prove a small amount of TV is even a small waste. (3) Supporting example: sleep — half the day of sleeping is a waste, but some sleep is positively necessary (a beneficial reversal). The same dose-response flip as vitamin A. Identical structure to the original.

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

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