The pronunciation of S at the end of plural nouns, verbs in the third person, and as a part of the possessive case sometimes causes confusion for non-native English speakers because it can be pronounced differently in 3 ways: / ɪz /, / s / or / z /.
In English, the pronunciation depends on the last sound of the verb or noun, which is usually a consonant.
But before we discuss the pronunciation rules on ‘s’ sounds, it would be necessary to have a review of the different consonant sounds we have in the English language: The Voiced Sounds, The Voiceless Sounds, and the Sibilant Sounds.
Voiced consonants require the use of the vocal cords to produce their signature sounds. These sounds produce a vibration or humming sound in the throat when they are said. Put your finger on your throat and then pronounce the letter d. You will notice a slight vibration in your neck/throat. Other voiced sounds are g, b, v, etc.
Voiceless consonants do not use the vocal cords to produce their hard, percussive sounds. Instead, they’re slack, allowing air to flow freely from the lungs to the mouth, where the tongue, teeth, and lips engage to modulate the sound. For example, k, p, f, etc.
Another sound that is relevant to this is the sibilant sound which is produced by forcing air out toward your teeth. It is characterized by a hissing sound (sssss), a buzzing sound (zzzzz) or the sound teachers make when they want you to be quiet (shhhh!).
Z like the sound a bee makes… zzzzzz
S like the sound a snake makes… sssssss
SH like the sound a teacher makes when they want you to be quiet… shhhhh
And now that you already know the difference between voiced, voiceless, and sibilant sounds, we can look at the following rules for the correct pronunciation of S at the end of words in English.
Always remember that the pronunciation of the final S in plural words and verbs in the third person depends on the final consonant sound before that S.
After a voiceless sound, we pronounce the ending ‘s’ as /s/.
However, we pronounce the ‘s’ as /z/ after a voiced sound.
Lastly, the ‘s’ is pronounced /ɪz / or /əz/ after a sibilant sound.