Here's a handout on nouns which I give my students to help them understand irregular plural noun forms.
In English, nouns are divided between the singular and plural form. To make a noun plural, an 's' is usually added to the singular but there are several exceptions to the rule.
Nouns that in ch, s, sh, x, or z form the plural by adding 'es' to the singular. It's because these words which end in ch, s, sh, x or z would be difficult to pronounce if only an 's' were added. Here are some examples:
Nouns that end in 'y' which are preceded by a consonant form the plural by changing the 'y' to 'i' and then adding an 'es'. Here's an example:
Nouns that end in 'f' form the plural by changing the 'f' to 'v' and then adding an 'es'. Here are some examples:
Nouns that end in fe form the plural by changing the f to v and then adding only an 's'. Here are some examples:
Finally, there are many irregular plural noun forms which one must commit to memory. Here are some examples: