Irregular Plural Nouns: Definition & Example

Instructor: Lauren Posey

Lauren has taught intermediate reading in an English Language Institute, and she has her Master's degree in Linguistics.

Most English nouns follow a standard set of rules for becoming plural nouns. In this lesson, you'll learn about some nouns that break these rules, and the different ways they become plural.

Nouns, Nouns, Everywhere

Have you ever watched a group of dogs playing in a park? Or noticed leaves falling off of trees? The need for plural nouns is a constant in day-to-day life. If you're a native speaker of English, you may not have thought much about the pluralizing process, but there are a standard set of rules. Most nouns follow these rules, making them regular nouns. For many regular nouns, simply adding an 's' on the end is all that is needed. However, if it ends in 'ch,' 'sh,' 's,' 'x,' or 'z,' you would need to add 'es' instead. All in all, regular nouns are fairly straightforward.

So, what about the nouns that don't follow this pattern? Though they may not be in the majority, there are quite a few of them. In fact, if you noticed the leaves on the trees, you've already used one! These are called irregular nouns, and there are a number of different ways they can become plural.

Irregular Plural Patterns

Most irregular nouns are not by any means random. They do follow a pattern, it just happens to be a different pattern from the one that regular nouns follow. This fact, and the fact that they follow several different patterns, is what sets them apart from the regular nouns. Let's take a look at some of these patterns now.


One irregular plural pattern is the changing of 'f' to 'v' at the end of the noun. If a noun ends in '-fe,' the 'f' changes to 'v,' and an 's' is added. For example, 'life' changes to 'lives,' and 'knife' becomes 'knives.'

Similarly, if a noun ends in '-f,' the 'f' becomes a 'v,' and 'es' is added. Some examples of these are 'half,' which changes to 'halves,' and 'wolf,' which changes to 'wolves.' As you can see, with both the 'f' and 'fe' ending, the result is that the plural form ends in 'ves.'


Another irregular plural pattern is seen in words ending in '-us.' In this case, the 'us' changes to become an 'i.' You can see this in these nouns:

  • Cactus becomes cacti
  • Nucleus becomes nuclei

-Is and -On

Another type of irregular noun that follows a pattern is nouns that end with '-is.' In these cases, the 'is' becomes an 'es' in the plural form. By this pattern, 'thesis' becomes 'theses,' and 'crisis' becomes 'crises.'

Finally, we can see a pattern in nouns that end with '-on.' In the plural form, the 'on' changes to an 'a.' That is how we get words like 'criteria' (from 'criterion') and 'phenomena' (from 'phenomenon').

Patternless Plurals

Not all irregular plural nouns follow a pattern this way. There are numerous examples of ones that have completely irregular plurals to which a rule cannot be assigned. Some, for example, change the central vowel. We see this in the 'man' to 'men' change, as well as in 'foot' to 'feet.'

In some cases, the plural form is completely different (other than the first letter), such as in 'person' to 'people,' and 'mouse' to 'mice.' On the other hand, there are some where the plural and the singular forms are exactly the same, such as deer and sheep.

What all of these cases have in common is that there is no pattern, and they simply have to be memorized. This lack of pattern becomes especially clear when we compare nouns that are similar in their singular form, but have completely different plurals.

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account