Baby becomes babies. City becomes cities. Spy becomes spies. The spelling changes from -y to -ies, but how does the sound change? Many learners pronounce it like /aɪz/ when it should be /iz/. Here's the rule that prevents this mistake.
The Spelling Rule
When a word ends in a consonant + y, the y changes to i and -es is added to form the plural (or third-person verb).
- baby → babies
- city → cities
- fly → flies
- study → studies
If the y comes after a vowel, no change happens:
- boy → boys (vowel + y)
- day → days
- key → keys
The Pronunciation Rule
The -ies ending is pronounced /iz/, with the long tense /i/ vowel from "see" and a voiced /z/ at the end.
Not /aɪz/ (like "eyes"). Not /ɪz/ (like the end of "buses"). Always /iz/.
Why Learners Get This Wrong
Three common mistakes:
- Reading the I as long /aɪ/: "babies" sounds like "BAY-byes." Wrong - it's "BAY-beez."
- Thinking /ɪz/ from -es: "babies" sounds like "BAY-biz" (short i). Wrong - the i is tense.
- Hearing the silent E: assuming the E adds a syllable like "buses." Wrong - no extra syllable.
Practice Words
Same Rule for Verbs
Third-person singular verbs follow the exact same pattern:
- study → studies /ˈstʌdiz/
- try → tries /traɪz/ wait! See exception below.
- worry → worries /ˈwɜriz/
- carry → carries /ˈkæriz/
The One-Syllable Exception
One-syllable words ending in consonant + y also follow the spelling change, but the vowel sound stays /aɪ/, not /i/.
| Singular | Plural / 3rd person | Pronunciation |
|---|---|---|
| spy | spies | /spaɪz/ |
| cry | cries | /kraɪz/ |
| fly | flies | /flaɪz/ |
| try | tries | /traɪz/ |
| fry | fries | /fraɪz/ |
| sky | skies | /skaɪz/ |
Why? In one-syllable words, the y carries the stress and is pronounced /aɪ/ as a long-I diphthong. The plural just adds /z/ to that, giving /aɪz/.
In multi-syllable words, the final -y is unstressed and is the tense /i/ from happy tensing (see our happy-tensing post). When you add -es, the /i/ stays and you simply add /z/, giving /iz/.
The Decision Test
- Look at the singular form. Is it one syllable? → /aɪz/ (spies, flies).
- Multi-syllable? → /iz/ (cities, babies).
- Vowel + y? Don't change spelling, just add /z/ (boys, days, keys).
Listen for the Voicing
The /z/ in -ies is always voiced. You should feel a buzz at the end of "babies," not a hiss. Compare:
- babies /ˈbeɪbiz/ - throat buzzes
- basis /ˈbeɪsɪs/ - just a hiss, no buzz
If you hiss, you've turned -ies into -is. Voice it.
Common Mistakes
| Wrong | Right | Word |
|---|---|---|
| /ˈbeɪbɪs/ | /ˈbeɪbiz/ | babies |
| /ˈsɪtaɪs/ | /ˈsɪtiz/ | cities |
| /ˈpɑrtaɪs/ | /ˈpɑrtiz/ | parties |
| /ˈstʌdaɪs/ | /ˈstʌdiz/ | studies |
Speed Drill
Read this sentence aloud, focusing on every -ies as /iz/ except the one-syllable ones:
"The babies in the cities heard stories about spies and ladies who fly in the skies."
- babies, cities, stories, ladies → /iz/
- spies, skies → /aɪz/ (one-syllable origin: spy, sky)
- fly is a verb, plural-style ending here would be "flies" /flaɪz/
Why It Matters
Plural -ies is one of the most common endings in English. Saying it wrong is a constant tell. The rule is simple: multi-syllable → /iz/, one-syllable → /aɪz/. Practice with a few common words and your plurals will sound right every time.