The vast majority of nouns in the English language are made plural by adding an "s" or "es" to the end of the word. For example, book, apple, house, table, door, cat, bush, boss are just some of the millions of words that become plural with the simple addition of an "s" (books, apples, houses, tables, doors, cats, bushes, bosses). However, certain nouns have "irregular" plurals which do not behave in this standard way.

Regular Plurals

For most nouns, the general rule for making the word plural is:

• If the word ends in s, x, ch or sh, add an "es"

Bless + es = blesses

Box + es = boxes

catch + es = catches

Dish + es = dishes

• If the word ends in a consonant (all letters except a, e, i, o, u) + y, then change the "y" to an "i" and add the letters "es"

Baby = Babies

Candy = candies

• For all other non-irregular nouns, simply add an "s" to the end of the word

Cat = cats

Dog = dogs

Kid = kids

Irregular Plurals

Certain words do not follow the above rules for regular plurals. There are some common types of irregular plurals that occur, and some words simply have no plural form at all.

While it is useful to memorize the common irregular plurals, for many words you simply have to know and understand that it is an irregular plural as a result of speaking and hearing English. 

Non-Count Nouns

Non-count nouns, also called collective nouns, have no plural form because they are assumed to be plural. Most abstract nouns are non-count nouns. Some examples are:

• Hair
• Grass
• Mud
• Dress (when referring to a style of dress, not when referring to a clothing item that hangs in your closet)

If you are talking about multiple varieties or types of these irregular plurals, you cannot make them plural by adding an "s" or "es" to the end.  Instead, you need to make them plural by adding a descriptive phrase.  For example:

• There are many different styles of hair
• There are several varieties of grass
• There are three different kinds of mud
• The ancient people had a few types of styles of dress

Unchanging Nouns

Certain other nouns have the same plural form as singular form. A large number of animals happen to follow this rule. For example, among others:

• Deer is "deer" whether singular or plural
• Fish is "fish" whether singular or plural
• Bison is "bison" whether singular or plural
• Moose is "moose" whether singular or plural
• Elk is "elk" whether singular or plural. 

Other Irregular Plurals

In addition to non-count nouns and unchanging nouns, there are several different types of irregular plurals which follow a pattern in the English language.

• For words that end in "fe," you change the letter "f" to the letter "v" and then add "s"

Knife = knives

Wife = wives

• For words that end in "f" you change the "f" to a "v" and add "es"

Half = halves

Loaf = loaves

• For words that end in "us," change the "us" to an "i"

Syllabus = syallabi

• For words that end in "o" add "es"

Tomato = tomatoes

Words that Change Form

Certain words do not add a letter to the end, but instead change the word itself. These words simply need to be memorized. Some examples include:

• Man to men
• Person to people
• Tooth to teeth
• Goose to geese

The best way to learn and understand irregular plurals is to practice speaking the English language, to read a great deal, to pay attention to words and phrases that you see and hear and to assemble a list of words with irregular plurals so you can begin to understand how to make each noun plural correctly.