Irregular Plurals: 6 Rules You Must Know

How easy would all languages be if every tiny aspect of it followed a simple rule! Imagine if you could say that yesterday you buyed a sweater, or that your cat catched three mouses this week. Everything would be so simple and perfect for language learners…What a wonderful life this would be, right? But well, life’s not that simple and neither are languages. That’s why this post is here, to help you cope with the irregularities of the English language. In this case, we’re focusing on irregular plurals.

Irregular Plurals In English

What are irregular plurals?

Irregular plurals are plural forms of countable nouns which are not constructed by adding -s or -es to a noun. An example of an irregular noun is “louse”, whose plural form is “lice”.

How to construct irregular plural nouns

The fact that they are irregular means that there isn’t one single rule that applies to all of them. However, irregular nouns can be grouped into categories according to the way they change from singular to plural. The changes may be grouped as follows:

1. Changing “-f” or “-fe” –> “-ves”: 

Some plural nouns are constructed by changing the final “-f” or /f/ to “-ves“.

wolf –> wolves; dwarf –> dwarves; shelf –> shelves; knife –> knives; life –> lives; etc.

2. Changing some vowels

Some plural nouns are formed by changing the vowels within the singular form.

man –> men; woman –> women; goose –> geese; foot –> feet; tooth –> teeth; etc.

3. Latin/Greek plurals

Many nouns which come from Latin or Classical Greek suffer particular changes when constructing the plurals:

“-is” –> “-es”: basis –> bases; analysis –> analyses; crisis –> crises; oasis –> oases; etc.

“-us” –> “-i”: cactus –> cacti; focus –> foci; nucleus –> nuclei; etc.

“-um” –> “-a”: curriculum –> curricula; minimum –> minima; referendum –> referenda; etc.

“-ex” –> “-(i)ces”: index –> indices; matrix –> matrices; codex –> codices; etc.

“-a” –> “-ae”: formula –> formulae; vertebra –> vertebrae, etc.

“-on” –> “-a”: phenomenon –> phenomena; criterion –> criteria; etc.

“-ma” –> “-mata”: dogma –> dogmata; stigma –> stigmata; etc.

For a comprehensive list of irregular Latin plurals, read the Latin Plurals article by Oxford Dictionaries.

4. Adding “-(r)en”

Although extremely rare these days, there are a couple of common ones:

child –> children

ox –> oxen

5. Other changes

The nouns that follow are also irregular nouns, but don’t follow any of the rules above specifically:

person –> people

testes –> testis

penny –> pence

mouse –> mice; louse –> lice; die –> dice

6. Plurals with no change

The following nouns have the exact same spelling and pronunciation for their singular and plural forms:

  • many animals: sheep; deer; fish; moose; duck; salmon; trout; etc.
  • other: series; species; etc.

With these 6 guidelines you will pretty much be able to cope with most irregular plurals. However, you must take into account that some of the singular nouns above might also have a regular form. This one may or may not have the same use/meaning as the irregular one. According to Oxford Dictionaries:

In some cases more than one form is in use, sometimes with a usage distinction (appendix/appendices/appendixes, formula/formulae/formulas) and sometimes with no clear distinction (cactus/cacti/cactuses).

As mentioned above, let’s take a quick look at the usage of “appendix” to see the difference in meaning:

Another common example is “mouse”. If we talk about the tiny rodent we must use “mice”, whereas we can say “mouses” if we’re referring to the plural form of a PC mouse.

This kind of thing of information about the English language that is cool to know even if it’s not entirely necessary to pass some exams like LanguageCert B1 or LanguageCert B2.

If you would like to read more about this subject, I encourage you to follow the links at the end of the post, in the references section. You will find many more examples and information that will help you understand this important aspect of English.

If you would like to learn more, don’t forget to follow Keep Smiling English on FacebookTwitter and YouTube!

Until next time, don’t forget to Keep Smiling!

Picture of Luis @ KSE Academy

Luis @ KSE Academy

Luis Porras Wadley is the owner and director of KSE Academy, an English academy and official Cambridge Exam Preparation Centre based in Granada. As an English teacher, Luis has been preparing Cambridge candidates successfully for more than ten years. He is the author of some successful test preparation books, including Speaking First, Speaking CAE, Speaking CPE, Use of English C1 and The Ultimate B2 First Writing Guide.

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