Possible Duplicate:
When did it become correct to add an ‘s’ to a singular possessive already ending in ‘s’?
Which singular names ending in “s” form possessives with only a bare apostrophe?

Which one is correct?
I thought the latter would be correct but apparently the former is always used; why?

Edit:

Another (confusing) example: Charles'(s?) law

marked as duplicate by tchrist, TimLymington, Mitch, user2683, J.R. Nov 26 '12 at 9:12

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If Bayes had discovered it today, we might call it Bayes's theorem, pronounced baizes to rhyme with mazes. However, Thomas Bayes lived in the 18th century, and the theorem was published in 1763. I believe that before the 20th century, the rules for pronouncing possessives may have been slightly different (this isn't completely standardized; different people still treat the pronunciation of possessives like Jones'(s) differently today), so we call it Bayes' theorem, pronounced bays to rhyme with maze. Note that in the Wikipedia article I linked to they use Bayes's death, but Bayes' theorem.

The earliest reference I can find in Google books to Bayes' rule (1854) spells it Bayes's. However, it seems that when it became widely discussed in the early 1900s with increased investigation of probability, it was generally referred to as Bayes'.

This Ngram shows that before around 1900, Charles's was the dominant spelling, but after 1900, Charles' became more common.

  • Not sure I buy the 1763 thing... would that make it Charles's or Charles'? – Mehrdad Nov 25 '12 at 20:57
  • Actually, after a little more searching, I don't buy it either. The most prevalent form seems to be Bayes's (usually applied to some other Mr. Bayes) from 1600 through 1900. I think Charles's behaves differently because it's nearly counts as two syllables. – Peter Shor Nov 25 '12 at 22:01

You will find many grammarians who tell you that if the noun ends in s and is singular, an 's is still used. This is disputable, as per this wikipedia discussion:

If a singular noun ends with an s-sound (spelt with -s, -se, for example), practice varies as to whether to add 's or the apostrophe alone. A widely accepted practice is to follow whichever spoken form is judged better: the boss's shoes, Mrs Jones' hat (or Mrs Jones's hat, if that spoken form is preferred). In many cases, both spoken and written forms differ between writers.

My best advice is: be consistent.

  • Not the answer I was hoping for... but it's the most consistent with the evidence so far, haha. =P +1 – Mehrdad Nov 25 '12 at 20:57
  • Grammarians are immaterial. Simply listen to what people say, then write that down. See here. – tchrist Nov 25 '12 at 20:58
  • 1
    @tchrist, then we could absolutely exclude the exisistence, in the present or in the past, of deaf-mute grammarians. Or not? – user19148 Nov 25 '12 at 21:42
  • 2
    @Carlo_R. - not if you are a Bayesian, although you could weight you prior estimate against it – mgb Nov 25 '12 at 21:51
  • Obligatory link: xkcd.com/1132 – Mehrdad Nov 25 '12 at 22:50

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