English is, thankfully, not a very irregular language when it comes to nouns. The vast majority of nouns form the plural by simply adding -s or -es. A handful of nouns are completely irregular, such as “women”, “men”, or “children”, but non-native speakers usually learn very fast not to use the -s form in these cases.
What causes much greater trouble are nouns that do not change at all in the plural, i.e. you have to recognize the plural from the context. “Sheep” and “fish” are two notorious examples:
There are three fish in the pond.
As you can see, we do not add -s to form the plural form. Here is a list of nouns that follow the same pattern, always with an example of use (you can read about a special case of nouns that end with an “s” in the singular in a separate article):
- aircraft, hovercraft, spacecraft, and other “-craft” vehicles
There are two aircraft prepared for landing.
- bison: The bison were grazing in the distance.
- cod: The cod are known to migrate in large numbers.
- deer: Deer are easy prey for wolves.
- ﬁsh: Three ﬁsh swim in the ﬁsh tank.
- moose: Moose actually belong to the deer family.
- offspring: The fox gave birth to ﬁve offspring.
- pike: The pike are big freshwater predatory ﬁsh.
- salmon: Salmon are often seen jumping over dangerous waterfalls.
- sheep: One sheep, two sheep, three sheep…
- shrimp: Shrimp are among the most commonly eaten animals.
- swine: Swine are reared extensively in Europe.
- trout: The trout are ﬁsh related to the salmon.
Note that many species of ﬁsh were left out from the list. Referring to ﬁsh using the same singular and plural form is extremely common, but actual usage varies somewhat among different regions, so it is advisable to consult a dictionary when writing about a particular species.
Also note that the names of animals mentioned above are sometimes used in the plural to refer to several species bearing the same name, for example:
Furthermore, there are a few nouns that can take either regular or irregular plural forms:
- boar: He saw several boar(s) in the woods.
- buffalo: I hope there aren’t too many buffalo(e)(s) outside.