In general the plural of a noun is formed by adding -S to the noun.
1. When the noun ends in S, SH, CH, X or Z*, we add -ES to the noun.
- I have a box in my bedroom.
- I have three boxes in my bedroom.
* With words that end in Z sometimes we add an extra Z to the plural form of the word (such as with the plural of quiz).
2. When the noun ends in a VOWEL + Y, we add -S to the noun.
3. When the noun ends in a CONSONANT + Y, we remove Y and add -IES to the noun.
4. If the noun ends in F or FE, we remove the F/FE and add -VES to the noun.
Some exceptions: roof – roofs, cliff – cliffs, chief – chiefs, belief – beliefs, chef – chefs
5. If the noun ends in a CONSONANT + O, we normally add -ES to the noun.
Some exceptions: piano – pianos, halo – halos, photo – photos
NOTE: Volcano has two correct forms of plural. Both volcanos and volcanoes are accepted.
6. There are a number of nouns that don’t follow these rules. They are irregular and you need to learn them individually because they don’t normally have an S on the end.
- There is a child in the park.
- There are many children in the park.
7. There are some nouns in English that are the same in the singular and the plural.
- I can see a sheep in the field.
- I can see ten sheep in the field.
Sometimes you will hear the word fishes (especially in songs) though it is grammatically incorrect.
The next rules are a lot more advanced and even native speakers have difficulty with these. Unless you are an advanced student, I wouldn’t recommend learning them just now.
8. If the noun ends in IS, we change it to ES. Words that end in IS usually have a Greek root.
9. If the noun ends in US, we change it to I. Words that end in US usually have a Latin root.
Some exceptions: octupus – octupuses (because it is from Greek, not Latin), walrus – walruses