Is there a hard rule for what sound the 's makes? In words like John's, Dave's, man's, lord's, etc. it makes a /z/ sound, but in words like that's, it's, ship's, poet's, etc., it makes an /s/ sound.

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    This may help: /s/ comes after words ending in vioceless sounds (sounds in the production of which the vocal cords are held wide apart; sounds in the production of which the vocal cords do not vibrate). Examples are /t/, /k/, /f/. /z/ comes after words ending in voiced sounds (sounds in the production of which the vocal cords are close together; sounds in the production of which he vocal cords vibrate). Examples are /d/, /m/ and /g/. /iz/ comes after words ending in sibilants. – FumbleFingers Feb 17 '16 at 21:54
  • Relevant question on the English Language Learners site: Rules for pronouncing prefixes and suffixes – herisson Feb 17 '16 at 21:54
  • One way of looking at it: In your second list the words end with a sort of percussive sound, whereas in the first list they do not. (This difference in pronunciation is quite intuitive to native English speakers. Though there may be a few oddball exceptions somewhere, in general there's no need to memorize a list or anything like that, even at a subconscious level.) – Hot Licks Feb 17 '16 at 22:12
  • I pronounce all the words above with the same ending 's' sound. If you use a 'z' sound, it's probably because that was the natural tendency of whoever taught you those words. Drawing the 's' out more will make it sound more like a 'z', that's all. – TylerH Feb 18 '16 at 15:50
  • Unlike the OP, I think I pronounce John's, man's and lord's with a /s/. – curiousdannii Feb 23 '16 at 7:01

If the final sound in the base of the word is voiced, we use the voiced alveolar sibilant /z/.

If the last sound in the base is an unvoiced consonant, we use /s/.

However, if the last sound in the base form is another sibilant of any description—/s, z, ʃ, ʒ, tʃ, dʒ/—we need to insert a vowel /ɪ/ to make the ending audible. Because this vowel is voiced the very last sound will be /z/. In other words, if the last sound is a sibilant we add /ɪz/:

  • /bʌs/ ---> /bʌsɪz/ (buses)
  • /bʌz/ ---> /bʌzɪz/ (buzzes)
  • /bʊʃ/ ---> /bʊʃɪz/ (bushes)
  • /ru:ʒ/ ---> /ru:ʒɪz/ (rouges)
  • /hʌtʃ/ ---> /hʌtʃɪz/ (hutches)
  • /bʌdʒ/ ---> /bʌdʒɪz/ (budges)
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  • @JohnFehr Indeed. Thanks, that's helpful. Maybe an easier way to think about it is /p, t, k, ʧ [as in church], f, θ, [as in thing], s, ʃ [as in she]/ and /h/ are all unvoiced. All the other consonants, and of course vowels, are voiced. – Araucaria - Not here any more. Feb 19 '16 at 15:34
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    It looks like phonemicchart.com/what/index3.html has a complete list of voiced/unvoiced phonetic sounds. I tried copying/pasting here, but couldn't figure out how to do the formatting. :P Also, if I'm not mistaken, all vowel sound are voiced. – John Fehr Feb 19 '16 at 15:35
  • @JohnFehr Exactly so! :) – Araucaria - Not here any more. Feb 19 '16 at 15:39

The word ending spelled apostrophe "s" is a phonemic /z/ in all the instances I can think of. (But English spelling is not very regular, so there could be exceptions.) However, English has a morphophonemic rule that converts a voiced obstruent (e.g. /z/) to the corresponding voiceless phoneme (for /z/ that would be /s/) when the /z/ is immediately preceded by a voiceless obstruent phoneme.

The term "obstruent" means that a sound is naturally voiceless, as compared with a "sonorant", which is naturally voiced. English vowels, nasal consonants, liquids, and glides are sonorants. Other English phonemes are obstruents.

The obstruents have a constriction in the mouth that retards the airflow sufficiently to prevent the vocal cords from vibrating without making some special articulatory adjustment (such as laxing the cheeks or lips to let them puff out, or dropping the jaw, both of which let the mouth cavity hold more air so air flow past the vocal cords can speed up). Many languages of the world do not have voiced obstruent phonemes, but English does have some, in addition to voiceless obstruent phonemes.

For determining whether a /z/ is preceded by a voiceless obstruent, what counts is the phonemic form of a word. Another morphophonemic rule of English inserts a vowel between two coronal obstruent fricatives or affricates, where "coronal" means that a sound is articulated with the tip or blade of the tongue. In "pitch's", e.g., a vowel is inserted between "pitch" and the ending "'s" (which is phonemic /z/), and so the /z/ is not changed to /s/, because /z/ is no longer immediately preceded by a voiceless obstruent.

This covers all the examples you mentioned, since none of /n,v,d/ is a voiceless obstruent, and all of /t,p/ are voiceless obstruents. I have used slashes for all the examples, rather than brackets indicating actual pronunciations, because I agree with you that this is a phonemic phenomenon and not a phonetic one.

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  • I'm confused about whether you're talking about phonemes or phonetics here. Shouldn't a phoneme’s notation like phonemic /z/ stay the same no matter how it gets pronounced phonetically under assimilation to phonetic [z] or [əz] or [ɨz] or [s] or [əs] or [ɨs] or whatnot? Or are we now venturing into the territory of some hypothetical /Z/ archiphoneme or however you want to represent such things? – tchrist Feb 11 '18 at 14:56
  • @tchrist, Yes, it should. Did I somehow imply otherwise? My answer does not mention any phonetic forms or archiphonemic forms (if there are such things), so I'm having difficulty understanding your question. Maybe you are doubting the existence of any rules which apply to phonemic forms and produce phonemic forms as a result? If so, we could discuss that. I (and others) call such rules "morphophonemic". – Greg Lee Feb 11 '18 at 16:09
  • My confusion is because you talk about when the phoneme /z/ becomes /s/. I had expected you to say [s] there. – tchrist Feb 11 '18 at 16:13
  • @tchrist, Then perhaps, as I suggested, you don't know about phonological rules, which apply to phonemic forms and produce phonemic forms as a result. My term for those is "morphophonemic rules" (in agreement with Kiparsky), but one might call them "morphological rules" instead. There were some classical phonemicists who did have "morphophonemic" forms as distinct from phonemic forms to avoid violating "separation of levels" (which I think was all nonsense). – Greg Lee Feb 11 '18 at 16:23

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