cats vs. dogs — why the plural -s isn't always "s"

Add an -s and it's all just "sss," right? Not quite.

cats ends in a crisp /s/, dogs ends in a buzzy /z/, and buses somehow grows an extra syllable. What's going on?

Good news: you don't have to memorize anything. The -s ending — plural nouns and third-person verbs alike — depends only on the sound right before it, and there are just three cases.

Case 1: /s/ — after a voiceless sound

If the last sound is voiceless (your vocal cords don't vibrate) — and it's not a sibilant — the -s is a clean /s/.

• cats /kæts/, books /bʊks/, hopes /həʊps/, laughs /lɑːfs/

cats isn't "cat-ss." The /s/ just snaps onto the /t/.

Case 2: /z/ — after a voiced sound

If the last sound is voiced (vocal cords vibrate) — a voiced consonant or a vowel — the -s is /z/.

• dogs /dɒɡz/, plays /pleɪz/, tables /ˈteɪblz/, cars /kɑːz/

Words ending in a vowel, like play and car, always take /z/.

Case 3: /ɪz/ — after a sibilant (s/z/ʃ/tʃ/dʒ)

Only when the word ends in a hissing or hushing sound does -s become its own syllable, /ɪz/. This is the only case that adds a beat.

• buses /ˈbʌsɪz/, boxes /ˈbɒksɪz/, watches /ˈwɒtʃɪz/, wishes /ˈwɪʃɪz/

A trick you don't have to memorize (same one as -ed): first check if the word ends in a sibilant (s, z, sh, ch, ge). If yes → /ɪz/, extra syllable. If no, put a finger on your throat and say the last sound. Buzzing → /z/. No buzz → /s/.

That's all three rules. Next time you hit an -s, check the sound before it first.

(CTA) Want to see the phonetics for every word instantly? PHONO annotates any English text with IPA — snap a photo or paste, hear it in UK or US accent.