A Tip for the Possessive Apostrophe
www.englishclub.com › possessive-apostropheIf the possessive noun is singular, always add an apostrophe + s. If the possessive noun does not end in -s (in its written form), always add an apostrophe + s. If the possessive noun is plural and ends in -s (and this is a characteristic feature of the large majority of plural nouns), just add an apostrophe. This is why you say James's books, the children's books, and even the boss's books.