Historian: Leibniz, the seventeenth-century philosopher, published his version of calculus before Newton did. But then Newton revealed his private notebooks, which showed he had been using these ideas for atleast a decade before Leibniz's publication. Newton also claimed that he had disclosed these ideas to Leibniz in a letter shortly before Leibniz's publication. Yet close examination of the letter shows that Newton's few cryptic remarks did not reveal anything important about calculus. Thus, Leibniz and Newton each indepedently discovered calculus.

Which one of the following is an assumption required by the historian's argument?

A) Leibniz did not tell anyone about calculus prior to publishing his version of it
B) No third person independendly discovered calculus prior to Newton and Leibniz
C) Newton believed that Leibniz was able to learn something important about calculus from his letter to him
D) Neither Newton nor Leibniz knew that the other had developed a version of calculus prior to Leibniz's publication
E) Neither Newton nor Leibniz learned crucial details about calculus from some third source.
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First Attempt 710 - first-attempt-141273.html

Will go with {E}
Because if Both scientists learned it from some other source then the conclusion that each discovered independently falls apart.
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I'm happy to help.

I don't have the highest opinion of this question. What is the source? I'm not sure I would give it high marks.

Here's my analysis.
A) Leibniz did not tell anyone about calculus prior to publishing his version of it
Weak. So what if Leibniz told his wife, his sister, his barber, etc. before he published? Irrelevant to the argument. Not correct.
B) No third person independently discovered calculus prior to Newton and Leibniz
So what if someone in China, unbeknowst to either of them, came up with it first? That would not change the fact that they both discovered it independently. Not correct.
C) Newton believed that Leibniz was able to learn something important about calculus from his letter to him
This is a very good distractor wrong answer. This is the assumption of the minor conclusion, viz. Newton's claim "that he had disclosed these ideas to Leibniz", but it is not the assumption of the main conclusion and therefore not the assumption of the argument. Not correct.
D) Neither Newton nor Leibniz knew that the other had developed a version of calculus prior to Leibniz's publication
Tricky. The passage makes reasonably clear that Leibniz did not understand Newton's "cryptic remarks" and therefore didn't realize that Newton had discovered calculus already. What about the other way around? Think about Newton, after he had discovered calculus, after he had been using it in his notes for a while --- suppose at that point, he caught a whiff of a rumor that Leibniz was going to publish calculus. Even if Newton heard this rumor before Leibniz published, it wouldn't make a bit of difference. In fact, Newton was so hyper-arrogant, I have no trouble imagining him hearing the rumor, shrugging his shoulders, and thinking, "I bet he won't do as superb a job as I have done!" It is certainly possible that Newton heard about Leibniz's work before Leibniz published, and this would not make any difference. They both still would have discovered calculus independently. Not correct.
E) Neither Newton nor Leibniz learned crucial details about calculus from some third source.
We've eliminated the other four, so we hope this is correct! I must say, as a correct answer, I am not happy with this one. It's true, if we negate it --- if both Newton & Leibniz learned about calculus from the same earlier source, then their derivations would not be independent. In that sense, it's an assumption of the argument. BUT, it feels like it is going too far outside the text, straying into a topic that one would not consider relevant. It feels like it went much further outside the scope of the original argument than the GMAT would typically do in a CR question. Yes, it's clear to me that whoever wrote the question was thinking of this as the correct answer. What I am questioning is the worth of the question itself; it seems to me that it doesn't capture the spirit of GMAT CR very well, and in that sense, I would be inclined to call the source, whatever it is, entirely into question.

Reluctantly, I'll say (E) is the answer, but I'll also say --- whatever book produced this, you could probably toss this book into the recycling bin and your GMAT preparation would be no worse for the wear.

Please let me know if you have any further questions.

Mike
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Mike McGarry
Magoosh Test Prep