Mastering English grammar isn’t just about memorizing rules, it’s about noticing the exceptions too.
One of the trickiest yet most essential parts of grammar is understanding irregular plural nouns.
These quirky rule-breakers don’t follow the usual -s or -es pattern, and if you’ve ever wondered why “man” becomes “men” or “child” becomes “children,” you’re in the right place.
In this guide, we’ll explore what irregular plural nouns are, their types, and how to use them naturally in everyday sentences.
What are Irregular Plural Nouns?
Irregular plural nouns are words that don’t follow the usual rule of adding -s or -es to form their plural.
Instead, they change in unique ways—or sometimes don’t change at all! These words break the “standard” grammar rule, which is why they’re called irregular.
For example, the plural of man is men, not mans, and child becomes children, not childs.
Learning them takes a bit of memorization, but they’re very common and essential in everyday English.
Types of Irregular Plural Nouns
Irregular plural nouns come in several different forms. Here are the main types:
1. Change of Internal Vowel
Some irregular plural nouns change their internal vowel sound instead of adding “-s” or “-es.”
This type of change is very common and easy to spot once you’re familiar with it.
This vowel shift doesn’t follow modern spelling rules, and these words are still frequently used in everyday conversations. For example:
- Man → Men
- Foot → Feet
- Tooth → Teeth
- Goose → Geese
- Woman → Women
2. Different Word Entirely
In a few special cases, the plural form is completely different from the singular, with no connection in spelling.
These are some of the oldest words in the English language and follow their own unique grammatical patterns.
They don’t have a visible rule–you just have to memorize them. For example:
- Person → People
- Child → Children
- Ox → Oxen
- Die → Dice
- Mouse → Mice
3. No Change At All
Some nouns look exactly the same in both singular and plural forms. So whether you’re talking about one deer or ten, the word deer stays the same!
These words usually refer to animals or scientific terms and make context especially important when identifying singular or plural. For example:
- Sheep → Sheep
- Deer → Deer
- Fish → Fish
- Species → Species
- Aircraft → Aircraft
4. Words Ending In -us
Latin-origin nouns that end in -us often become -i in the plural. These words are often used in biology, physics, or other scientific fields.
Some of them also have more modern plural forms like cactuses, but cacti is still widely accepted and preferred in formal settings. For example:
- Cactus → Cacti
- Fungus → Fungi
- Focus → Foci
- Nucleus → Nuclei
- Stimulus → Stimuli
5. Words Ending In -is
Nouns ending in -is, which often come from Latin or Greek, usually change the -is to -es in their plural form.
They sound sophisticated but are essential for formal writing or technical communication. For example:
- Crisis → Crises
- Thesis → Theses
- Analysis → Analysis
- Diagnosis → Diagnoses
- Hypothesis → Hypotheses
6. Words Ending In -on or -um
Some nouns that end in -on or -um, mostly scientific or academic terms, switch to -a when pluralized.
These forms are particularly useful in academic writing and professional discussions. For example:
- Phenomenon → Phenomena
- Bacterium → Bacteria
- Datum → Data
- Criterion → Criteria
- Curriculum → Curricula
20 Examples of Sentences with Irregular Plural Nouns
Here are 20 simple and practical sentence examples to help you see how irregular plurals work in context:
- The men are playing soccer in the park.
- The fish are swimming near the coral reef.
- Several children were drawing on the sidewalk.
- These geese fly south every winter.
- The teeth need to be brushed twice a day.
- She saw a few mice in the attic.
- The women are attending a leadership seminar.
- A group of deer ran across the road.
- We studied several theses during the literature class.
- The doctor analyzed multiple diagnoses.
- The botanist collected rare fungi.
- The cacti in the garden are blooming.
- These data are crucial for the report.
- My feet hurt after the hike.
- All the alumni were invited to the ceremony.
- I read articles about recent crises in the news.
- The syllabi were distributed on the first day of class.
- Several phenomena were observed during the experiment.
- People often confuse those two terms.
- The oxen were used to plow the field.
Conclusion
Now that you’ve uncovered the secrets behind irregular plural nouns, it’s time to put them into practice!
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