Module 1, Nouns, Lesson 5:

Irregular Plural Nouns


Irregular nouns form plurals in unusual ways. Dictionaries will give you the plural spelling if it is irregular.

one child ⇒ two children
one foot ⇒ two feet
one tooth ⇒ two teeth
one man ⇒ two men

Some nouns are spelled the same way whether they are singular or plural.

one fish ⇒ two fish
one sheep ⇒ two sheep
one deer ⇒ two deer

Nouns with Latin and Greek origins form plurals in strange ways. Because Latin and Greek plural endings are so unusual, many people try to follow the English rules by adding s or es. Applying the English rules is acceptable for some nouns, but using the original spelling is usually better. You will notice in the chart below that nouns with the same endings form plurals in the same way every time. Impress your friends and family by knowing the correct forms.

-a ⇒ -ae -us ⇒ -i -is ⇒ -es -on ⇒ -a and -ie ⇒ -ce
amoeba ⇒ amoebae alumnus ⇒ alumni analysis ⇒ analyses criterion ⇒ criteria
antenna ⇒ antennae cactus ⇒ cacti axis ⇒ axes phenomenon ⇒ phenomena
alumna ⇒ alumnae fungus ⇒ fungi diagnosis ⇒ diagnoses die ⇒ dice
nucleus ⇒ nuclei hypothesis ⇒ hypotheses
octopus ⇒ octopi parenthesis ⇒ parentheses
Amoebas, cactuses, and funguses are now acceptable spellings even though the Latin spellings are still preferred. Also, octopuses is now the preferred plural spelling of octopus, but the Latin octopi is acceptable as well.

Some nouns exist only in the plural form.

binoculars pants
clothes pajamas
glasses scissors
goggles shorts
jitters tweezers
Note: This is not a complete list.

Depending on the style manual you use, there are different rules for making letters, numbers, and abbreviations plural. The information in this lesson is based on the Chicago Manual of Style. Use the shortcuts in this lesson to help you remember the rules.

  • In order to make capital letters plural, add a lowercase s. Sometimes it is necessary to use an apostrophe if the plural form could be confused with a word (such as the word As versus the plural A's or the word Is versus the plural I's), but the apostrophe is only necessary if the letter is at the beginning of the sentence.

    Shortcut: Capital letter + s

    I earned straight As on my report card, but my sister received all Bs.

  • To make lowercase letters plural, italicize the letter and add an apostrophe + s. It is important to add the apostrophe because otherwise the letter might be mistaken for a word (for example, a's versus as). Remember that even though the letter itself is italicized, the s is never italicized.

    Shortcut: Lowercase italicized letter + apostrophe + s

    Why does algebra use so many x's and y's?

  • To make an abbreviation plural, simply add a lowercase s. It is not necessary to add an apostrophe before the s.

    Shortcut: Abbreviation + s

    I used to have a lot of CDs, but now I just listen to my mp3 player.
    I've heard that M.D.s go to school for at least 7 years!

  • One last area that we haven't covered is how to make numbers plural. You can do so by adding a lowercase s without an apostrophe.

    Shortcut: Number + s

    2s, 3s, and 4s

    Many people think that you have to use an apostrophe + s when making years plural, but most style guides actually suggest that you leave out the apostrophe.

    The Industrial Revolution took place between the late 1700s and early 1800s.
    I was born in the '90s.

    (Notice how the apostrophe in '90s comes before the number. That's because the apostrophe is being used to replace the 19 in 1990s. It has nothing to do with whether the number is plural or not.)

Remember that the Chicago Manual of Style isn't the only guide out there, and different manuals follow different guidelines. For example, some manuals prefer to use an apostrophe + s when making all letters and numbers plural. When writing, consult your manual if you have one. Whether you have a manual or not, make sure to follow the same rule throughout your essay, article, or story.

Also remember that people use specific guides for certain types of writing. Some popular guides are the Associated Press Stylebook (also called the AP Stylebook), APA style (from the American Psychological Association), and the MLA style (from the Modern Language Association). When you write essays or research papers, you use MLA or APA style, but when writing a news article, you use the AP Stylebook. If you're not sure which guide to use, just ask your teacher.

Practice What You've Learned

Exercises are reserved for account holders.
Please log in.

 Need an account?
Sign up to get started.

Click the word that represents the correct plural form of the noun in bold.
larva - larvas ... larvaes ... larvae ... larvi
trout - trouts ... troutes ... trout ... trouta
bison - bisons ... bisones ... bisonae ... bison
moose - moose ... mooses ... meese ... moosae
salmon - salmons ... salmon ... salmonae ... salmoni
mouse - mouses ... mice ... meese ... mousi
formula - formulaes ... formula ... formulae ... formuli
nucleus - nucleuses ... nuclea ... nuclei ... nucleum
crisis - crisises ... crisi ... crises ... crisea
stimulus - stimulus ... stimuluses ... stimulae ... stimuli