-s, -es plural ending; 3rd singular present ending,
▷ -'s possessive singular ending;
▷ -s', -es' possessive plural ending s, z, ɪz əz —There are three regular pronunciations:
After a sibilant ( BrE AmE s, z, ʃ, ʒ, tʃ, dʒ ), the pronunciation is ɪz or, less commonly in British English but usually in American English, əz , as faces ˈfeɪs ɪz -əz , Mitch's ˈmɪtʃ ɪz -əz . (In singing, exceptionally, a strong-vowelled variant ez is usual if the spelling is es , as ˈfeɪs ez .)
Otherwise, after a voiced consonant ( b, d, ɡ, v, ð, m, n, ŋ, l , American English r ) or a vowel sound, the pronunciation is z , as names, name's neɪmz ; after a voiceless consonant ( p, t, k, f, θ ), the pronunciation is s , as cats, cat's kæts .
—Certain nouns whose last sound is a voiceless fricative switch it to a voiced fricative before the plural and plural possessive endings. The ending naturally then takes the form z . The change is shown in spelling in the case of f —v ( wife waɪf — wives, wives' waɪvz ), but not for θ —ð , s —z ( mouth maʊθ — mouths, mouths' maʊðz ). In the possessive singular and with the contracted forms of is and has , there is no such change ( wife's waɪfs , mouth's maʊθs ).
—With proper names ending in a sibilant, usage varies. Usually, the possessive is pronounced regularly, though the spelling may vary: Jones' , Jones's ˈdʒəʊnz ɪz AmE ˈdʒoʊnz əz . Less commonly, the possessive ending is unpronounced ( dʒəʊnz AmE dʒoʊnz ); the corresponding spelling is then Jones'.