What Is an Irregular Plural Noun? Usage Guide and Examples

For most plural nouns in English, adding "s" or "es" to the end of the word changes a singular noun into a plural noun (friend becomes friends, wristwatch becomes wristwatches, and so on). But with irregular plural nouns, that’s not the case.

Examples of irregular plural nouns include:

• parties
• mice
• moose
• scissors
• men
• wives
• tomatoes

Irregular plural nouns either change their endings (such as party to parties) or stay the same as their singular forms (such as moose to moose). It may seem like they’re just breaking grammar rules, but really, irregular plural nouns are just following different spelling rules.

Just because they’re called irregular doesn’t mean these plural nouns are uncommon. In fact, you’ll find many of them in your everyday speech.

Many irregular nouns change their endings when they move from singular to plural. Once you know how each noun’s spelling changes, you’ll make fewer spelling mistakes.

If the word ends in a consonant plus "y," then change the "y" to an "i" and add the letters "es.”

When a word ends in a vowel and “y” (such as monkey or day), you just add an “s” to the end (monkeys, days).

For most nouns that end in "f" or "fe," drop the "f" or "fe" and add "ves."

When a noun ends in a double vowel and an “f” (such as roof or proof), it doesn’t change to “ves” in the plural form. Instead, just add an “s” to the end (roofs, proofs).

For many words that end in “us,” change the “us” to an “i” (especially if it comes from a Latin word). There are exceptions to this rule, and it’s becoming more acceptable to add “es” instead of changing to “i” in some cases — especially if the word has a Greek root.

Another Latin spelling convention turns singular nouns that end in "um" into plural nouns that end in “ia.”

Some irregular plural nouns do end in "es" — but you don't just add it to their endings. For many words that end in “is,” change the “is” to an “es.” These are also pronounced differently (ees at the end of each word, not es)

Parties, bacteria, and cacti at least follow their own rules. But certain irregular plural nouns, such as children or teeth, don’t follow any grammatical rules at all. The only way to get them right is to memorize them.

Just as you were mastering the irregular plural nouns that change their endings, here come the nouns that don’t change at all. The good news is, you only need to learn one spelling — the bad news is, there’s no rule about which words follow this rule.

Uncountable nouns don’t have plural forms. They usually describe an uncountable quantity of something (such as air or love).

Many nouns have the same singular and plural forms, especially species of animals. You can only tell that they’re plural by reading the context clues in the rest of the sentence.