"This car belongs to Tom" is also written as "This is Tom's car".
How do I write "This car belongs to Yves"?
Is it Yves'
, or Yves's
?
How to form the possessive of a singular noun ending in 's' is a style question; usage varies (http://www.grammarbook.com/punctuation/apostro.asp). If you have a style guide to which you are expected to adhere, then it should address this question. If you have no other guidance, then choose an approach and stick to it.
The standard variations are indeed the ones you present. Some styles call for using one form or the other for all categories of nouns, and some distinguish between the form used with proper nouns and the one used with common nouns. There may be other approaches, too. Given the choice, I personally use 's
to form the plural of every singular noun, regardless of its spelling or whether it is common or proper.
I believe either form is technically correct for names that end in S.
Personally I prefer the Yves's form, just because I think it makes the possessive clearer, but it just depends on the writer's preference and what style they're using.