Noun Plurals (US)

You're finishing a story for class, and you need the plural of mouse. You already know cat becomes cats, so mouse should become mouses, right? You write it, and it comes back with a red circle around "mouses." Annoying — especially since "just add -s" works for almost every other noun you know.

Here's the deal: English plurals mostly follow patterns. Add an -s, sometimes an -es, and you're done for the vast majority of words. But a small group of very common nouns — child, mouse, foot, person — refuse to play along, and a few others (sheep, series) don't change at all. Once you see why, these stop being random exceptions and start being patterns you can predict.

This is the US English edition — American spelling throughout. There's a matching UK English article if you're studying British spelling or exam-board rules.

The basic rules

A singular noun names one thing (one book); a plural noun names more than one (two books). For most nouns, you make the plural by adding -s: pen → pens, teacher → teachers, game → games.

But say "bus" and add just an -s: "buss." It doesn't sound right, so English adds -es whenever a word ends in a hissing or buzzing sound — s, ss, x, z, ch, sh: bus → buses, box → boxes, church → churches, dish → dishes. Say each pair out loud and you'll hear that extra "-ez" syllable.

Some nouns ending in -o also take -es, especially short everyday ones: tomato → tomatoes, hero → heroes. Others just take -s: piano → pianos, photo → photos, video → videos. There's no clean rule — checking a dictionary when you're unsure is exactly what I'd do too.

Common Mistake: Writing "buss" as the plural of bus. The plural is buses — "buss" is actually a rare old word meaning "kiss."

Spelling changes and irregulars

Nouns ending in -y. Look at the letter right before the y. Consonant → change y to ies: baby → babies, city → cities, party → parties. Vowel (a, e, i, o, u) → just add -s: boy → boys, key → keys, day → days. "Babys" sounds off; "boys" is completely natural.

Nouns ending in -f or -fe. Some switch to -ves: leaf → leaves, knife → knives, wolf → wolves, life → lives, wife → wives. Others just add -s: roof → roofs, chief → chiefs, belief → beliefs. A few allow both (scarf → scarfs or scarves). There's no perfect rule — you learn the -ves ones through reading.

Common irregular plurals. Some of the most-used nouns change completely, with no -s at all:

• child → children · person → people
• man → men / woman → women
• foot → feet / tooth → teeth
• mouse → mice / goose → geese

There's no spelling shortcut here — you just have to know them, and because you use them constantly, they stick fast.

Nouns that don't change. Some look the same whether you mean one or many: one sheep → two sheep; one deer → several deer; one fish → three fish; one series → two series; one species → many species. The verb tells you which: "a sheep is grazing" versus "the sheep are grazing."

Common Mistake: Writing "childs" or "peoples" when you mean more than one child or person. It's children and people. ("Peoples" is a real word, but only for different nations or ethnic groups — "the indigenous peoples of North America.")

Pro-Tip: When you're unsure on a -y word, underline the letter right before the y. Consonant underlined? Switch to ies. Vowel underlined? Just add -s.

Compounds, foreign plurals, and plural-only nouns

Plurals of compound nouns. A compound noun is made of two or more words acting as one: mother-in-law, runner-up, editor-in-chief. To pluralize these, you make the main noun — the "head" — plural, not just whichever word sits at the end. Mother-in-law is about the mother, so the plural is mothers-in-law, not "mother-in-laws." Same logic gives you runners-up, editors-in-chief, and passersby. Closed compounds — written as one word, like bookshelf and toothbrush — just take a normal ending at the very end: bookshelves, toothbrushes.

Pro-Tip: To find the head noun, ask "Two what?" Two mothers-in-law. Three runners-up. That's the part you pluralize.

Foreign and classical plurals. English borrowed heavily from Latin and Greek, and a lot of those words now allow two correct plurals — a classical one and a regularized English one:

• curriculum → curricula / curriculums
• cactus → cacti / cactuses
• syllabus → syllabi / syllabuses

Others are more fixed, and using -s on these looks like a mistake to anyone who knows the word:

• criterion → criteria (never "criterions")
• phenomenon → phenomena (never "phenomenons")
• analysis → analyses / crisis → crises / thesis → theses

In science class you'll meet Latin plurals a lot: "Several bacteria were observed under the microscope." In everyday writing, the -s form is often fine: "We moved the cactuses into the greenhouse."

Common Mistake: Adding an extra -s to a word that's already plural, like "criterias" or "phenomenons." Criteria and phenomena are already plural forms — there's no need to pluralize them twice.

Plural-only nouns. A small, stubborn group of nouns are always plural and never appear in true singular form: scissors, pants, jeans, glasses (the kind you wear), pajamas, binoculars. They take plural verbs — "My scissors are in the drawer," not "is" — and to talk about just one, you say "a pair of": a pair of scissors, a pair of jeans.

UK vs US Note

This article covers US English patterns throughout. The core rules are the same worldwide — dogs is plural everywhere — but a few spellings and preferred forms differ across the Atlantic. British English, for instance, talks about the storeys of a building where American English says stories — a genuine spelling difference. British writing also leans a little more toward classical plurals like fora where American writing prefers forums. If you're studying British English or working with a UK exam board, read the UK edition, or the dedicated comparison article for a side-by-side look.

Quick check

1. Make these nouns plural: box, story, leaf, child, mother-in-law.

2. True or false: Sheep changes form when you mean more than one.

3. What's the plural of criterion — and why is criterias wrong?

4. Fix the mistake: "Two sheeps and three deers walked across the road."

5. Which is correct: "The scissors is on the desk" or "The scissors are on the desk"?

Where next

• What Is a Noun? for a refresher on noun basics before diving into plurals.
• Countable and Uncountable Nouns for words like information and furniture that behave differently from ordinary plurals.
• Possessive Nouns and Apostrophes for how plurals and possessives interact.
• US vs UK Noun Plurals Compared for a side-by-side look at the differences.
• The UK English edition of this article, for learners studying British English.
• Nouns: The Complete Guide for the foundational article this piece builds on.