Some nouns have identical singular and plural forms. Examples are: swine, sheep, deer, cod, salmon, aircraft, spacecraft, series, species etc.
The following nouns are always used in the singular form after numerals: pair, dozen, score, gross, hundred and thousand
- I bought three dozen mangoes. (NOT I bought three dozens mangoes.)
- The music player cost me two hundred dollars.
- He weighs above nine stone.
Note that the plural of fish is fish or fishes. In modern English, fishes is used to talk about different kinds of fish.
Some nouns are used only in the plural. Examples are: bellows, scissors, tongs, spectacles, trousers, drawers, jeans, breeches, tights, shorts etc.
A number of nouns ending in -s are in fact singular. Examples are: mathematics, physics, electronics, news, measles, mumps, rickets, billiards, innings etc.
- Mathematics is his favorite subject.
- No news is good news.
- West Indies won by an innings and three runs.
- Measles is highly contagious.
A few collective nouns, though singular in form, are always used as plurals. Examples are: cattle, poultry, people, gentry etc.
- These poultry are mine. (NOT This poultry is mine. )
- Vermin destroy property and spread disease.
- Who are these people?
The following nouns are always used in the singular. Examples are: luggage, news, advice, information, news, furniture, scenery etc.
- Kashmir is known for its scenery. (NOT Kashmir is known for its sceneries.)
- We have received no information. (NOT …no informations)
- We need to buy some furniture. (NOT …some furnitures.)