The Editor’s Manual
Free learning resource on English grammar, punctuation, usage, and style.
Form the possessive of a plural name by placing an apostrophe after the “s” that makes the plural, as you would for any other plural noun.
Form the plural of a given or a family name by adding “s.” If the name ends in a sibilant sound (like “s,” “x,” “z”), add “es” instead.
Add “s” to form the plural of a name ending in a vowel. Don’t add “es,” even for names ending in “i” or “o.” Simply add “s” (“the Rossis,” not “Rossies”). Avoid using an apostrophe (“the Lees,” not “Lee’s”).
Form the plural of a name ending in “z,” “x,” “sh,” “s,” and other sibilant sounds by adding “-es” without an apostrophe (“the Diazes,” “the Hendrixes,” “the Williamses”).
Form the plural of a name ending in “s” by adding “es,” not “ses” or an apostrophe and “s” (“the Harrises,” not “Harrisses” or “Harris’s”).
Form the plural of a name ending in “y” by adding “s” without an apostrophe. Don’t replace the “y” with “ies”; simply add “s” after the “y”: “the Murphys,” not “Murphies.”
Form the possessive of a name ending in “s” by adding either an apostrophe and another “s” or just an apostrophe. Both are acceptable in formal writing.
Possessive forms of nouns (with an apostrophe either before or after an “s”) and pronouns (without an apostrophe) indicate a relationship of belonging.