Logical ReasoningDifficulty: Hard

PT130 S3 Q18 Explanation

It was once thought that pesticide TSX-400

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

TopicsPrinciple-Strengthen

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Stimulus

It was once thought that pesticide TSX-400 was extremely harmful to the environment but that pesticides Envirochem and Zanar were environmentally harmless. TSX-400 was banned; Envirochem and Zanar were not. However, according to recent studies, Envirochem and Zanar each cause greater environmental harm than does TSX-400. If Zanar should be banned or TSX-400 should be legalized.

What this question is testing

Principle-Strengthen

Your task

Break the argument into its conclusion and evidence, then do exactly what the question stem asks with that structure.

Common trap

Answers that sound relevant to the topic but don't connect to the argument's actual reasoning.

Winning move

Predict what a right answer must do, then test each choice against the conclusion-evidence gap.

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 principles, if valid, most helps to justify

Answer choices

  1. Bad Conclusion Match13% picked this

    Two pesticides should not both be legal if one is measurably more harmful to the environment

    If we know that E and Z are more harmful than TSX, this rule tells us that they shouldn’t all be legal. But the author’s conclusion is allowing for them to all be legal. So this doesn’t match the author’s argument.

  2. Bad Conclusion Match4% picked this

    Two pesticides should both be legal only if neither is harmful

    If we know that E and Z and TSX are harmful to the environment, this rule tells us that they shouldn’t all be legal. But the author’s conclusion is allowing for them to all be legal. So this doesn’t match the author’s argument.

  3. Bad Premise Match9% picked this

    Two pesticides should both be illegal only if both are harmful

    This says “If at least one of these is not harmful to the environment, then they can’t all be illegal”. All three of the pesticides are harmful, so this rule is useless as it is inapplicable to the pesticides being discussed.

  4. Correct66% picked this

    One pesticide should be legal and another illegal only if the former is less harmful to the environment

    Why this is right

    This says, “If A is legal and B is illegal, then A must be less harmful than B”. The contrapositive, “If A is at least as harmful as B, then you can’t have A be legal and B be illegal.” This matches well with the argument: If E and Z are at least as harmful as TSX, then you can’t have E and Z be legal while TSX is illegal.

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

  5. Bad Premise Match8% picked this

    One pesticide should be legal and another illegal if the former is harmless to the environment and the

    This says, “If A is harmless and B is harmful, then A should be legal and B should be illegal”. We don’t have any harmless pesticides being discussed here, so this rule is inapplicable to our situation and thus useless.

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