A noun can be countable or uncountable. Countable nouns can take the indefinite article (a / an) in their singular form, and they have a plural form. The quantifiers some, a few etc., are used with countable nouns. We also use many with countable nouns.
- A book, two books, three books, some books .....
- An apple, two apples, three apples, a few apples ....
- A sock, two socks, three socks, too many socks ....
Uncountable nouns (also called mass nouns or noncount nouns) cannot be counted as separate objects. This means you cannot make them plural by adding -s, because they only have a singular form. It also means that they do not take the indefinite article (a/an) or a number in front of them.
We indicate the quantity of uncountable nouns (also called mass nouns or noncount nouns) by combining them with a countable expression (a piece of, a slice of etc), or a quantifier like some / a little / a lot etc.) in front of them. We also use much with uncountable nouns.
- Some water
- A lot of work
- A piece of information
- Too much coffee
- A bucket of sand
Sources of confusion with countable and uncountable nouns
The notion of countable and uncountable things can be confusing.
For example, money. We can count money can't we? Yes, but we count it in currencies - a million dollars / pounds / euros etc. (For some reason the yen is treated as an uncountable noun - a million yen).
Some nouns can be countable or uncountable depending on their meaning. Usually a noun is uncountable when used in a general, abstract way (when you don't think of it as a separate object) and countable when it has a very particular meaning (when you can think of it as a separate object).
glass - Two glasses of water. (Countable) | A window made of glass. (Uncountable) | glasses - I wear glasses. (Always plural)
Some supposedly uncountable nouns can behave like countable nouns if we think of them as being in containers, or one of several types.
This is because 'containers' and 'types' can be counted.
Believe it or not each of these sentences is correct:-
Doctors recommend limiting consumption to two coffees a day.
(Here coffees refers to the number of cups of coffee)
You could write; "Doctors recommend limiting consumption to two cups of coffee a day."
The coffees I prefer are Arabica and Brazilian.
(Here coffees refers to different types of coffee)
You could write; "The types of coffee I prefer are Arabica and Brazilian."
!Note - In good monolingual dictionaries, uncountable nouns are identified by [U] and countable nouns by [C].