1. One form, different numbers
English often forms plurals with -s or -es. Some countable nouns, however, have the same form for one item and several. This is an unchanged, or zero, plural: the word gains no new ending.
Here we practise five words: fish, sheep, deer, aircraft, meaning a flying machine such as an aeroplane, and series, meaning a TV series or a sequence of related things. Learn a short pair with each: one sheep — two sheep. These forms are broadly classified as irregular plurals because they do not follow ordinary -s formation.
one sheep → two sheep; one deer → two deer; one aircraft → two aircraft; one series → two series
One sheep is near the gate. Two sheep are in the field.
One sheep is near the gate. Two sheep are in the field.
Sheep is identical in both sentences, but one and two establish different numbers.
We can see three aircraft.
We can see three aircraft.
Aircraft stays unchanged after three.
2. Identifying number without an ending
Number is visible beyond numerals. A/an, one, this and that can identify one item; two, many, these, those and both identify several. A verb or preceding turn can also clarify number.
The alone does not establish number. I can see the deer can mean one deer or several and needs wider context. Do not infer a plural merely because a is absent.
this / that + singular; these / those / many / both + plural
Those deer are near the road.
Those deer are near the road.
Those identifies several animals; are agrees with the plural.
I can see the aircraft.
I can see the aircraft.
Without further information, aircraft can be singular or plural here.
I like these series.
I like these series.
These marks a plural, although like after I does not distinguish the number of series.
3. The noun stays unchanged but agreement changes
An unchanged form does not keep the whole sentence unchanged. Present statements with be use is for one item and are for several. Demonstratives change too: this → these, that → those.
When changing singular to plural, check the whole phrase: quantity expression, noun and verb. Negatives follow the same principle: is not for one, are not for several. Contractions isn’t and aren’t are also possible.
This sheep is… → These sheep are…; That aircraft is not… → Those aircraft are not…
This deer is small. These deer are small.
This deer is small. These deer are small.
Deer stays unchanged; this/these and is/are identify number.
Those aircraft are not old.
Those aircraft are not old.
Negation does not cancel agreement: those is plural, requiring are not.
4. Series: -s belongs to the word itself
Series already ends in -s in the singular. Do not remove it for one series or add a new ending for several.
A series is one TV series or one sequence of related things. Two series are two TV series or two sequences. Our everyday exercises mainly use series for a whole TV series rather than one episode.
a series / this series is → two series / these series are
This series is short.
This series is short.
One series: retain final s and use is.
Both series are interesting.
Both series are interesting.
Two separate series: keep the spelling but use are.
5. Fish and fishes: avoid an unnecessary ban
When counting fish, the usual unchanged plural is fish: one fish, five fish. Fishes is also an accepted plural. It occurs, for example, for fish species, but is not restricted to that use alone.
Do not automatically label two fishes ungrammatical. An exercise explicitly requesting an unchanged plural requires fish; that is the selected learning form, not a prohibition on the other English form.
There are five fish in the tank.
There are five fish in the tank.
Fish is the usual plural without a new ending.
We saw two fishes.
We saw two fishes.
Fishes is an accepted plural. It is not an unchanged form, but does not itself make the sentence incorrect.
6. An unchanged plural is not uncountability
Sheep, deer, aircraft and series are countable: a sheep, several sheep; one series, two series. Having no new ending does not make them uncountable nouns.
Fish for an individual animal is also countable. For fish as food, it can be uncountable. Identify the contextual meaning rather than just the word’s appearance. Detailed uncountable-noun rules are studied separately.
How many sheep are in the field?
How many sheep are in the field?
We count animals, so use how many even without a plural ending on sheep.
There is some fish on my plate.
There is some fish on my plate.
Fish means food here rather than a count of individual animals: another, uncountable sense.
7. Using the rule in your own sentence
First decide whether you mean one item or several. Name it with the right word without adding an unnecessary ending. Finally, check any demonstrative and verb present in the sentence.
You can express number without an exact count: some sheep, those deer, both series. If several phrasings fit, meaning and grammar matter rather than literal repetition of the example. Safe everyday fictional situations are acceptable in your answers.
Look at those sheep. They are near our car.
Look at those sheep. They are near our car.
Those and they are consistently maintain the plural across both sentences.
I like this series, but those two series are too long.
I like this series, but those two series are too long.
You can compare one item and several in your own opinion while preserving the same series form.
Common mistakes
Incorrect:There are six sheeps in the field.
Correct:There are six sheep in the field.
Extra -s: ordinary plural sheep has the same form as singular sheep.
Incorrect:These aircraft is new.
Correct:These aircraft are new.
These identifies several aircraft, requiring are; an unchanged noun does not cancel agreement.
Incorrect:This serie is short.
Correct:This series is short.
One TV series is also series. Its final s is not a plural ending to remove for the singular.
Incorrect:That sheep are small.
Correct:That sheep is small.
That identifies one sheep: change only are to is.
Incorrect:How much sheep are here?
Correct:How many sheep are here?
Individual animals are counted, requiring many rather than much.