A common question I get from pronunciation clients is how we know when to say /s/ or /z/ when there’s an -s ending on words in English. Here are rules to help. It’s important to note that the rules for pronouncing the -s ending are different than the rules for pronouncing the -ed ending.

Why and when do we add an -s to the end of words?

There are 3 main uses of the -s ending in English, and they are all extremely common:

1. to form the plural of a noun (1 house–> 2 houses)
2. to form the singular present tense (he/she/it makes)
3. to indicate possession (the boy’s mom).

In these examples, the -s ending on houses sounds like /ɪz/, while the -s on makes is pronounced /s/, and the -s on boy’s is pronounced /z/.

There are 3 rules that can guide you on when to say which one.

When does an -s ending say a voiceless /s/?

The /s/ sound is a voiceless sound made without any vibration of the vocal chords.

When the base word ends in a voiceless consonant, then the -s ending is pronounced as a voiceless /s/…. most of the time. This rule is true for all the voiceless consonants except the sibilants, which have their own rule (explained below).

So, when the -s is added to any base word ending in /p/, /t/, /k/, /f/ or /θ/, the -s is pronounced as a voiceless /s/, like in the following words.

• cap /kæp/ → caps /kæps/
• cat /kæt/ → cats /kæts/
• back /bæk/ → backs /bæks/
• cliff /klɪf/ → cliffs /klɪfs/
• bath /bæθ/ → baths /bæθs/

When does an -s ending say a voiced /z/?

When the base word ends in a voiced sound (a vowel or a voiced consonant), then the -s ending is usually pronounced as a voiced /z/. The exception, again, is if the consonant is a sibilant.

Consider the following base words that end in vowel sounds:

• key /kiː/ → keys /kiːz/
• play /pleɪ/ → plays /pleɪz/
• sky /skaɪ/ → skies /skaɪz/
• show /ʃoʊ/ → shows /ʃoʊz/
• shoe /ʃuː/ → shoes /ʃuːz/
• spa /spɑː/ → spas /spɑːz/
• bra /brɑː/ → bras /brɑːz/
• law /lɔː/ → laws /lɔːz/

And here are examples of base words ending in voiced consonants:

• cab /kæb/ → cabs /kæbz/
• bed /bɛd/ → beds /bɛdz/
• bag /bæɡ/ → bags /bæɡz/
• stove /stoʊv/ → stoves /stoʊvz/
• bathe /beɪð/ → bathes /beɪðz/
• bell /bɛl/ → bells /bɛlz/
• car /kɑːr/ → cars /kɑːrz/
• room /ruːm/ → rooms /ruːmz/
• pen /pɛn/ → pens /pɛnz/
• song /sɔŋ/ → songs /sɔŋz/

When does an -s ending say a voiced /ɪz/ as an extra syllable?

There is a group of sounds that are somehow related to the s, which are called sibilants. The sibilant sounds in English can be voiced or unvoiced. They include the /s/ and the /z/, as well as /ʃ/, /ʒ/, /tʃ/, and /dʒ/. (In the spelling, these sounds are often represented by sh, g, ch, dge or tch)

When an -s is added to a base word that ends in a sibilant, we add another syllable and pronounce it /ɪz/.

Consider the following words:

• bus /bʌs/ → buses /bʌ sɪz/
• buzz /bʌz/ → buzzes /bʌ zɪz/
• brush /brʌʃ/ → brushes /brʌ ʃɪz/
• garage /ɡə rɑːʒ/ → garages /ɡə rɑː ʒɪz/
• watch /wɑtʃ/ → watches /wɑtʃ ɪz/
• judge /dʒʌdʒ/ → judges /dʒʌ dʒɪz/

Review: 3 Rules for knowing when to say /s/ or /z/

1. -s = /s/ after most voiceless consonants
2. -s = /z/ after vowels and most voiced consonants
3. -s = /ɪz/ after voiced or unvoiced sibilants

Practice these sentences:

• The boys stayed at home with Pete’s friend and watched movies all day.
  • boys /bɔɪz/, Pete’s /pits/, movies /mu viz/
• He catches baseballs better than he hits them.
  • catches /kæt ʃɪz/, baseballs /beɪs bɔlz/, hits /hɪts/
• On most mornings, she brushes her hair and puts make-up on before 7am.
  • mornings /mɔr nɪŋz/, brushes /brʌ ʃɪz/, puts /pʊts/

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