Jim's teacher asked him to

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

TopicsFlaw

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Stimulus

Jim's teacher asked him to determine whether a sample of a substance contained iron. Jim knew that magnets attract iron, so he placed a magnet near the substance. Jim concluded that the substance became attached to the magnet.

What this question is testing

Flaw

Your task

Describe the reasoning error the argument actually commits.

Common trap

Answers that name a real logical flaw the argument doesn't actually make.

Winning move

Articulate the gap in the reasoning yourself, then match it to the choice that describes that 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

Jim's reasoning is questionable in that it fails to consider the

Answer choices

Not an Objection3% picked this
iron sometimes fails to be attracted
This gets at the notion that we might get a False Negative when we test for iron. Just because a magnet isn't attracted to something wouldn't prove there's no iron in it, because sometimes iron isn't attracted to magnets.
3%
Not an Objection5% picked this
iron is attracted to other objects
This would fight a move from "Since iron was attracted to this thing, this thing must be a magnet". But our author never made that move so pointing out that iron is attracted to other things has no impact on the author.
5%
Not an Objection1% picked this
the magnet needed to be oriented in a
Like (A), this sounds like an objection we would make if the author were saying, "Thus, there is NOT iron in the substance". We would sound the alarm about False Negatives: nuh-uh ... sometimes iron just fails to attract to a magnet ... sometimes you just need to orient the magnet the correct way. We need an objection that would allow us to argue that this substance is not iron. This answer isn't helping us to argue that Anti-Conclusion.
1%
Correct90% picked this
magnets attract substances other than
Why this is right
This gives us the False Positive objection we're looking for ... "Just because the magnet was attracted doesn't prove that it is iron. Magnets are attracted to copper and nickel, too, so maybe the substance is made of copper or nickel, not iron."
Skill tested: Flaw · how this choice captures the argument's function is the move to repeat next time.
90%
Out of Scope Comparison: more strongly2% picked this
some magnets attract iron more strongly
We aren't concerned with the relative level of attraction. If we were fighting a move from "Since the magnet wasn't attracted, it isn't iron", we could respond with this False Negative objection of ... there's iron in there: the magnet test just failed because this type of iron doesn't attract strongly enough for Jim to have noticed any attraction.
2%

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