# Apostrophe after a surname

There is a lot of statistical criteria/tests (statistics) named after a statistician/mathematician/biologist/economist, etc. But for instance, this and this examples have different spelling...
Do I have to write an apostrophe after a surname in such a situation or not?

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Find what someone else wrote and use that. – Sam Oct 20 '11 at 4:26
– stan Oct 20 '11 at 11:29
An interesting case. There is a theorem that is often incorrectly written Stoke's Theorem. It should be Stokes' Theorem or Stokes's Theorem, since the man's name was Stokes. – GEdgar Oct 20 '11 at 14:37
an example – stan Oct 21 '11 at 2:00

There's an interesting discussion on this topic in Wikipedia talk.

Their conclusion:

I guess we just have to live with the fact that some theorems traditionally have apostrophes (Goedel's incompleteness theorem) and other's don't (Tietze extension theorem); it doesn't make sense to have a general rule of style there.

Go with tradition if you can find it, or with whatever manual of style you follow otherwise.

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It depends on how you refer to it, eg. "Fermat's last theorem" but "the Goldbach conjecture"

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The Goldbach conjecture is sometimes written as Goldbach's conjecture, but you'd never say, The Fermat's last theorem. (unless you were trying to distinguishing it from your cousin Fermat's theorem. – Sam Oct 20 '11 at 4:18
@Sam - yes if you wrote is as Goldbach's conjecture you would add the apostrophe. It was the first one I could think of that was generally "THE ....." – mgb Oct 20 '11 at 4:20
Doppler effect comes to mind. It would seem strange to say Doppler's effect. Ohm's Law, conversely, would sound funny as The Ohm Law. – Sam Oct 20 '11 at 4:37