Rules for the use of /s/, /z/ or /IZ/ as the ending for plural nouns.

When using the plural of nouns, they can end with /s/, /z/ or /IZ/ sounds. What are the rules for the use of these endings sounds? Could please someone give a simple explanation? Thanks in advance.  

Bernadette O' Sullivan

Hi Bernadette,

Good question! I remember very clearly when I learned the rule for this. It felt as if a veil had been lifted on a whole lot of things.

The answer to the question of a final /s/, /z/ or /Iz/ sound all has to do with the sound that precedes it.

To understand this, one first has to understand the concept of VOICED and UNVOICED consonants in English.

A voiced consonant sound is one in which the vocal cords vibrate. For example, /z/. If you make that sound and put your hand to your throat, then you should be able to feel it. Another way to tell if a sound is voiced is to put a finger in your ear and make the sound; (you should be able to hear the humming).

An unvoiced consonant sound is one in which the vocal cords do NOT vibrate. For example, /s/. Try the same test above while you are making the /s/ sound. No vibration, no humming. To really get the effect, try making a long /s/ and then going to /z/ (again, with a finger in your ear or hand on your throat).


Right. Now here come the rules:


If the singular form of the noun ends in a voiced consonant, then the plural will have the voiced /z/. Take the word BIN. The /n/ sound, if we apply our test, is voiced. So BINS has the /z/ ending. NOTE: If the noun ends in a vowel sound then it will also take the /z/ ending. This is because vowel sounds are voiced. For example: EYE – EYES (with /z/ sound)


If the singular form of the noun ends in an unvoiced consonant, then the plural will have the unvoiced /s/. Take the word BOOK. The /k/ sound is unvoiced. So BOOKS has the /s/ ending. This still doesn’t account for the /IZ/ though. For this, we need to understand that, in addition to voiced and unvoiced there is another sub-category of consonant called sibilants. The ‘s’, ‘z’, ‘sh’ and ‘tch’ sounds are sibilants.


If the noun ends in a sibilant, then add the /IZ/ sound for the plural.

The table below provides a summary of this with examples:

Voiced consonant + /z/ Vowel sound + /z/bins, bags, peas, boys
Unvoiced consonant + /s/
books, bats, lights
Sibilant + /IZ/ watches, kisses, wishes

What do your students need to know?

I know you asked for a simple explanation, but the above three rules are as simple as it can get while still being true. It’s useful to make your students aware of voiced and unvoiced consonants anyway, as they affect other areas of pronunciation.

However, there is a convincing argument that for students, especially lower level ones, the most important thing to know is whether or not to add an extra syllable (the /IZ/ sound). Either adding /IZ/ where it isn’t necessary or not adding /IZ/ where it is necessary are more common mistakes than making a /s/ sound instead of a /z/ sound. These mistakes are also more likely to cause confusion.

So, while I may point out the above three rules (to draw students’ attention to them), I therefore tend to focus mainly on whether or not to add an extra syllable. It is also the area I would correct more in students’ speaking.

How this knowledge can help in other areas

At the beginning of my answer I mentioned how excited I was when I discovered this rule, because I found it helpful in other areas. For example, everything we have mentioned about nouns + s is equally valid for verbs + s (i.e. the third person singular of the present simple). In addition, the concept of voiced + voiced and unvoiced + unvoiced (rules 1 and 2 above) also work for the –ed endings of regular verbs:

Voiced consonant + /d/opened, remembered
Unvoiced consonant + /t/
worked, watched
/t/ or /d/ + /Id/ ended, wanted

So, three areas of grammar and pronunciation for the price of one! Good luck with it.