Possessive case for a certain proper noun - ss apostrophe This is a style issue, not a matter of objective correctness or incorrectness Having said that, I note the advice that various style manuals offer From Words Into Type (1974): Proper names The possessive form of almost all proper names is formed by adding apostrophe and s to a singular or apostrophe alone to a plural By this style rule, you would express the plural of Ross as Ross's From