Logical ReasoningDifficulty: Hard

PT106 S2 Q18 Explanation

Dobson: Some historians claim that

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

TopicsFlaw

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Stimulus

Dobson: Some historians claim that the people who built a ring of stones thousands of years ago in Britain were knowledgeable about celestial events. The ground for this claim is that two of the stones determine a line pointing directly to the position of the sun at sunrise at the spring equinox. large. Therefore, the people who built the ring were not knowledgeable about celestial events.

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
18.

Which one of the following is an error of reasoning in

Answer choices

  1. Correct61% picked this

    The failure of cited evidence to establish a statement is taken as evidence that

    Why this is right

    This is one way to phrase the Unproven vs. Proven False flaw (other ways sound like, "treats a failure to prove as proof of failure" or "takes an absence of evidence as evidence of absence"). The cited evidence is the 2nd sentence: "the ground for this claim [that the ring-builders are knowledgeable] is that two stones point somewhere interesting". The author rebuts the logical force of that premise saying, "however, if you take any bunch of rocks that are randomly strewn about, there is still a large change that you can find two of them that end up pointing at something celestially interesting". The correct conclusion for the author to draw at this point should sound more undecided, more agnostic: - Thus, it would be premature to conclude that the ring-builders were knowledgeable about celestial events. - Thus, we'll need more compelling evidence before we believe the historians' claim. The author is not allowed to just assume the historians conclusion is a false claim, just because they supported it poorly. Whenever we're doing Flaw and we see that the author is rebutting someone else, we want to be on guard for two famous flaws: Ad Hominem (the author rejects their position because of their ulterior motive or past behavior) Unproven vs. Proven False (the author shoots down someone's rationale and then concludes the polar opposite of their original conclusion)

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

  2. Wrong Flaw: not Self-Contradiction13% picked this

    Dobson’s conclusion logically contradicts some of the evidence presented in support

    This describes another one of the ten famous flaws: Internal Contradiction. Dobson only has one piece of evidence, the 2nd to last sentence. It certainly does not contradict the conclusion in the final sentence. A contradiction would sound like: There are many stones, so the chance at least one pair points somewhere interesting is large. Therefore, it's very unlikely that any pair of stones would point somewhere interesting by random chance.

  3. Never a Flaw Reversed Ingredients5% picked this

    Statements that absolutely establish Dobson’s conclusion are treated as if they merely give some support

    This answer would be closer to describing reality if we reversed the order of ingredients: statements that merely give some support are treated as if they absolutely establish the conclusion. That would be similar to the semi-famous flaw Possible vs. Certain. It's bad to go overboard in the conclusion. If we establish that Karl is sniffling a lot and blowing his nose a lot, that supports the idea that he's sick, but it would be flawed to say "Thus, he is definitely sick". However, this answer choice is complaining that an author ended up saying a conclusion that is weaker than what we could have. Not only did that not happen here, but that wouldn't be a flaw even if it did happen. If we say, "Every NFL player has a Y chromosome and only biological males have Y chromosomes", those statements would absolutely establish the conclusion that "All NFL players are male". But it isn't flawed if we end up concluding, "Thus, some NFL players might be male." The fact that a more powerful conclusion would also be true doesn't make the weaker conclusion an invalid one.

  4. Wrong Flaw: not Opinion vs. Fact19% picked this

    Something that is merely a matter of opinion is treated as if it were subject to verification as

    This describes a semi-famous flaw Opinion vs. Fact. It would be appropriate if an author went from an opinionated premise to a factual conclusion, like, "Many people think that Ron Swanson moonlights as a locally famous saxophone player. Thus, apparently, Ron leaves work on some nights to go gig as a saxophonist." There, I treated a matter of opinion as though it were factual. There is a mix of fact and opinion in Dobson's argument, but our objection to his final move has nothing to do with treating an opinion as fact. Our objection is that even if the historians have shady grounds for their claim, that doesn't prove that their claim is untrue.

  5. Wrong Flaw: not Equivocation2% picked this

    Dobson’s drawing the conclusion relies on interpreting a key term in

    This describes the famous Equivocation flaw, in which an author uses the same term or concept in two very different ways. This answer is almost always wrong, and we only pick it when we can find a term being used twice in the argument and define it two completely different ways. There's no such term in this argument that gets used twice, to mean two very different things.

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