In general the plural of a noun is formed by adding -S to the noun.
1. When the noun ends in SS, SH, CH or X, we add -ES to the noun.
- I have a box in my bedroom.
- I have three boxes in my bedroom.
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.
5. If the noun ends in IS, we change it to ES.
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.