Is it correct to say "Forbes' building was sold to NYU" or "Forbes's building was sold to NYU" ? Or perhaps both are correct?
I was first taught that Forbes' was correct, but if you use Strunk and White's Elements of Style as you guide (as I prefer), you would use the latter.
The 1918 edition of Strunk's original book (and E.B. White concurred), he gives Rule 1 in Chapter 2, "Elementary Rules of Usage", as:
- Form the possessive singular of nouns with ’s
Follow this rule whatever the final consonant. Thus write,
- Charles’s friend
- Burns’s poems
- the witch’s malice
This is the usage of the United States Government Printing Office and of the Oxford University Press. Exceptions are the possessives of ancient proper names in -es and -is, the possessive Jesus’, and such forms as for conscience’ sake, for righteousness’ sake.
But such forms as
- Achilles’ heel,
- Moses’ laws,
- Isis’ temple
are commonly replaced by
- the heel of Achilles
- the laws of Moses
- the temple of Isis
The pronominal possessives hers, its, theirs, yours, and oneself have no apostrophe.
You'll get static from some folks who don't adhere to Strunk and White, but there's NOTHING wrong with this formation of the possessive in words ending with s.
Forbes' is correct. An example of that is a news article titled Oprah regains top spot on Forbes' list of most powerful celebrities (it's the first I found on Google, don't judge me).