When the article the is used before theorem names

Question

When writing math papers, one sometimes has to refer to some famous theorems, for instance, the Pythagorean theorem.

Shall I write "by Pythagorean theorem", or "by the Pythagorean theorem". When shall I use the article "the"?

I am not a mathematician, but did Pythagoras write any theorems other than the one about the square on the hypotenuse? If not, then my inclination would simply be to write re Pythagoras. — WS2, Commented Sep 12, 2015 at 23:43
The reference is to a unique theorem, so it should be definite: "by the Pythagorean theorem" or "by Pythagoras' theorem". It's like "the binomial theorem" or "the quadratic formula". — Greg Lee, Commented Sep 13, 2015 at 7:52
In this case "Pythagorean" is an adjective. Would the answer be the same for names which are not transforms into adjectives, for example: "Poisson process" vs "the Poisson process"? — Piotr Śniady, Commented Apr 30, 2020 at 8:19

chasly - supports Monica · Accepted Answer · 2015-09-12 22:42:46Z

4

This Google ngram shows what others have done in published books.

Notice that 'by Pythagorean theorem' has only one occurrence.

answered Sep 12, 2015 at 22:42

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user44400 · Accepted Answer · 2018-03-31 14:48:44Z

-2

"by Pythagorean Theorem"

For example, "I solved this equation using Pythagorean's Theorem," or, I solved expression 6 by using Pythagorean's Theorem."

I hope this helps!😁

user44400

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answered Sep 13, 2015 at 6:27

Lorrie_101

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I'm glad you want to participate, but "Pythagorean's Theorem" is not a valid construction. Maybe "a Pythagorean's Theorem" is theoretically possible, but not for this case. Anyway, people would be left wondering which Pythagorean.
– Spencer
Commented Mar 31, 2018 at 15:10

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