The English language has both regular and irregular plural forms of nouns. The most common case is when you need to add -s to the noun. For example one car and two cars.
The other two cases of the regular plural form are:
* nouns that end with s, x, ch or sh, where you add -es (e.g., one box, two boxes)
* nouns that end with consonant + y, where you change the y with i and add -es (e.g., one enemy, two enemies)
On the irregular plural form of nouns there are basically eight cases:
* nouns that end with -o, where you add -es (e.g., one potato, two potatoes)
* nouns ending with -is, where you change -is to -es (e.g., one crisis, two crises)
* nouns ending with -f, where you change -f to -v and add -es (e.g., one wolf, two wolves)
* nouns ending with -fe, where you change -f to -v and add -s (e.g., one life, two lives)
* nouns ending with -us, where you change -us to -i (e.g., one fungus, two fungi)
* nouns that contain -oo, change -oo to -ee (e.g., one foot, two feet)
* nouns that end with -on, where you change -on with -a (e.g., phenomenon, phenomena)
* nouns that don’t change (e.g., sheep, offspring, series)
It might appear overwhelming, but after using these nouns a couple of times you will be able to memorize their plural form easily.
English Grammar 101: Plural Form of Nouns
