The letter S looks like the most predictable consonant in English. It is not. Depending on its position, its neighbors and the history of the word, S can be pronounced /s/ (sun), /z/ (easy), /ʃ/ (sugar), /ʒ/ (vision), or nothing at all (island). This guide collects every rule in one place, with American English IPA, so you can predict the sound instead of guessing. It is part of our letter series: after the letter E, we are covering the consonants, starting with C, G, D and, here, S.
1. The default sound: /s/
When nothing special is happening, S is a voiceless hissing sound made with the tongue tip close to the ridge behind the upper teeth. Your vocal cords do not vibrate. This is the sound at the start of words (sun, sit, say), before or after voiceless consonants (stop, ask, lips), and in most final positions after a voiceless sound (bus, class, cats).
2. The voiced twin: /z/
/z/ is exactly the same mouth position as /s/, but with the vocal cords vibrating. Written S becomes /z/ in four situations.
2a. Between two vowels
A single S between vowel sounds is usually voiced: easy /ˈiːzi/, music /ˈmjuːzɪk/, visit /ˈvɪzɪt/, busy /ˈbɪzi/, reason, thousand. Exceptions (basic, crisis, research) are covered in intervocalic S.
2b. Final -s after a voiced sound
When a plural, third-person or possessive -s follows a vowel or a voiced consonant, it is voiced: dogs /dɑːɡz/, days /deɪz/, goes /ɡoʊz/, runs, cars, John's.
2c. Small function words
A short list of very frequent grammar words spell /z/ with a plain S: is, has, was, his, as, these, those, whose, because.
2d. Noun and verb pairs
Several words are written identically but switch between /s/ (noun or adjective) and /z/ (verb): use /juːs/ vs. use /juːz/, house /haʊs/ vs. house /haʊz/, close /kloʊs/ (near) vs. close /kloʊz/ (shut), excuse /ɪkˈskjuːs/ vs. excuse /ɪkˈskjuːz/. See when S sounds like Z for the full list.
3. The "sh" sound: /ʃ/
Two spelling contexts turn S into /ʃ/, the sound of she.
3a. SU + vowel right after the stressed syllable
sugar /ˈʃʊɡɚ/, sure /ʃʊr/, assure, insurance /ɪnˈʃʊrəns/, issue /ˈɪʃuː/, pressure. The rule and its /ʒ/ counterpart are the subject of our SU guide.
3b. -sion after a consonant, and -ssion
mansion /ˈmænʃən/, tension, pension, expansion, version /ˈvɝːʒən/ is the one common exception that many Americans pronounce with /ʒ/. Double SS before -ion is always /ʃ/: mission, passion, discussion.
4. The "zh" sound: /ʒ/
/ʒ/ is the voiced version of /ʃ/, the sound in the middle of measure. Written S produces it when -sion follows a vowel, and when -sure or -sual follow a stressed syllable: vision /ˈvɪʒən/, decision, conclusion, measure /ˈmɛʒɚ/, pleasure, treasure, usual /ˈjuːʒuəl/, casual, and the place name Asia /ˈeɪʒə/.
5. Silent S
A small group of words keeps a written S that is never pronounced. Most come from French: island /ˈaɪlənd/, isle, aisle /aɪl/, debris /dəˈbriː/, corps /kɔːr/ (the plural corps is /kɔːrz/), chassis, rendezvous, bourgeois, plus Illinois /ˌɪləˈnɔɪ/ and Arkansas /ˈɑːrkənsɔː/.
6. The plural, third-person and possessive -s
The grammatical ending has three pronunciations, chosen by the last sound of the base word:
- After a voiceless sound (/p t k f θ/): /s/. cats, books, laughs, months.
- After a voiced sound (vowels and /b d ɡ v ð m n ŋ l r/): /z/. dogs, days, pens, cars, sees.
- After a sibilant (/s z ʃ ʒ tʃ dʒ/): an extra syllable /ɪz/. buses, wishes, watches, judges.
The possessive 's and the contraction 's (he's, it's) follow exactly the same three-way rule: Pat's /s/, Bob's /z/, Rose's /ɪz/. Our three-sounds guide to -s endings drills all three.
7. Double SS
SS is a reliable signal for voiceless /s/: class, lesson, message, possible. Only three everyday words break the rule with /z/: scissors /ˈsɪzɚz/, dessert /dɪˈzɝːt/, and possess /pəˈzɛs/, where the second SS is /z/ but the final one is /s/.
8. The cluster SC
SC behaves like C: before E, I or Y the C is soft and the pair is /s/ (science, scene, scissors); before A, O, U or a consonant the pair is /sk/ (scan, scheme /skiːm/, school). Before an unstressed -ious or -ience, SC merges into /ʃ/: conscious /ˈkɑːnʃəs/, conscience. Full details in our letter C guide.
9. Quick decision flowchart
- Is the S part of a known silent-S word (island, aisle, Illinois, corps)? Then it is silent.
- Is it followed by -ion? Consonant + sion or ssion gives /ʃ/; vowel + sion gives /ʒ/.
- Is it SU + vowel after the stress (sugar, measure, usual)? /ʃ/ if the S was voiceless in the base word, /ʒ/ if it was voiced.
- Is it SC? Follow the C: /s/ before E, I, Y; /sk/ elsewhere; /ʃ/ before -ious.
- Is it a double SS? /s/ (except scissors, dessert, possess).
- Is it a grammatical -s ending? Match the previous sound: /s/, /z/ or /ɪz/.
- Is it a single S between vowels, or a function word like is, was, his, these? Probably /z/.
- Is it a noun/verb pair (use, house, close, excuse)? Noun /s/, verb /z/.
- Otherwise, /s/.
Summary table
| Sound | Typical spelling context | Examples |
|---|---|---|
| /s/ | word-initial, next to voiceless consonants, SS, SC + E/I/Y | sun, stop, class, science |
| /z/ | between vowels, -s after voiced sounds, function words, verbs of noun/verb pairs | easy, dogs, is, to use |
| /ʃ/ | SU + vowel after stress, consonant + sion, -ssion, SC + ious | sugar, tension, mission, conscious |
| /ʒ/ | vowel + sion, -sure, -sual, Asia | vision, measure, usual, Asia |
| /ɪz/ | plural or 3rd-person -es after a sibilant | buses, wishes, judges |
| silent | French loans, island, two state names | aisle, debris, island, Illinois |
Practice: quick self-test
Read each word aloud and decide which sound the S makes: /s/, /z/, /ʃ/, /ʒ/ or silent.
- reason
- tension
- aisle
- excuse (noun)
- pleasure
- boxes
- possess
- scheme
- his
- insurance
Answers:
- reason: /z/
- tension: /ʃ/
- aisle: silent
- excuse (noun): /s/
- pleasure: /ʒ/
- boxes: /ɪz/
- possess: /z/ then /s/
- scheme: /sk/
- his: /z/
- insurance: /ʃ/
Keep going with the sibling guides to letter C, letter G and letter D, then train the individual sounds on the consonant practice page.