Irregular plurals, unlike regular plurals, don’t necessarily follow any pattern, and require a lot of memorization. Mastering this type of pluralization uses a different region of your brain than regular pluralization, meaning it’s an entirely different skill set than regular pluralization. So don’t get too frustrated if you can’t remember the correct plural. If you’re ever in doubt, the dictionary is there for you.
No Change (Base Plurals)
In some words, the singular form is used for both singular and plural.
- fish
- deer
- sheep
- offspring
- series
- species
Mid-Word Vowel Change
In a few words, the mid-word vowels are changed to form the plural. This video lists all seven of these words and their plurals.
Plural –en
- child → children
- ox → oxen
- brother → brethren
- sister → sistren
Practice
What are the correct plurals for the following words?
| Singular | Plural | Singular | Plural |
|---|---|---|---|
| goose | moose | ||
| fish | child | ||
| man | tooth |
Borrowed Words –i, –en, –a, –es, –ae
In words borrowed from Latin and Greek, the plural from the original language is used.
Singular –us; Plural –i
- cactus → cacti
- fungus → fungi
- syllabus → syllabi
In informal speech, cactuses and funguses are acceptable. Octopuses is preferred to octopi, but octopi is an accepted word.
Singular -a; Plural –ae
- formula → formulae (sometimes formulas)
- vertebra → vertebrae
- larva → larvae
Singular –ix, –ex; Plural –ices, –es
- appendix → appendices (sometimes appendixes)
- index → indices
Singular –on, –um; Plural –a
- criterion → criteria
- bacterium → bacteria
- medium → media
Singular –is; Plural –es
- analysis → analyses
- crisis → crises
- thesis → theses
Practice
What are the correct plurals for the following words?
| Singular | Plural | Singular | Plural |
|---|---|---|---|
| memorandum | emphasis | ||
| focus | basis | ||
| nucleus | phenomenon | ||
| appendix | curriculum | ||
| parenthesis | hypothesis | ||
| stimulus | vertebra |
