This article covers pronunciation and spelling; the article on genitive covers usage.
The ending sound of the base word determines the pronunciation of the morpheme “-s”.
- /s/ for non-sibilant voiceless consonants /f/, /k/, /p/, /t/, and /θ/.
- Cardiff’s, Mike’s, sheep's, Egypt’s, Elizabeth’s
- /z/ for vowels and non-sibilant voiced consonants /b/, /d/, /ð/, /g/, /l/, /m/, /n/, /ŋ/, /r/, and /v/.
- Barbara’s, Bob’s, Maryland’s, Ann’s, Oscar’s
- /ɪz/ for sibilants: /s/, /z/, /tʃ/, /dʒ/, /ʃ/ and /ʒ/.
- virus’s, church’s, Marge’s, Bangladesh’s
- Not pronounced
- plurals ending in "s": dogs’, friends’
- classical and Biblical names: Augustus’, Jesus’, Moses’
Silent possessive is written as a single ’
- The dogs’ food (the food of the dogs)
- Jesus’ teachings
- singular noun + ’s: Peter’s friends gave him a great present;
- plural noun + ’: The athletes’ representative negotiated the deal;
- irregular plural + ’s: The women’s husbands were watching football on TV;
- We can add ’s or s’ to a whole phrase: Henry the Eighth’s six wives; Anne and John’s house in the country;
While the difference between plural possessives can be shown in written English it can be ambiguous in the spoken language. For example the pronunciation of (2) would be the same if it were:
- The athlete's representative ...
- The athletes’ representative ...
In practice, however, context usually makes things clear.
Lack of consensus
There's no consensus on how to use it with surnames ending in "s", for example "Davis". By way of example, until its 15th edition (2003), the Chicago Manual of Style recommended Davis', but in its 16th edition (2010), recommends Davis's. On the other hand, Oxford Dictionaries recommends the former.
Writers are recommended to spell as they pronounce. Davids’ is pronounced /ˈdeɪvɪdz/ and Davids’s is pronounced /ˈdeɪvɪdzɪz/.
Especial care must be taken in the use of the possessive apostrophe in titles. In the same way that we don't say or write *, we don't say or write *. The correct way is "Shakespeare's Tempest". We can also modify it and say "Shakespeare's last play The Tempest".
- Homer's Iliad - not: *