The grammar of mass and count nouns

Mass nouns are often the names of substances like water, wood and air that we can measure on a continuous scale. Count nouns, on the other hand, generally label things that come in discrete wholes that we can count like children, houses and hats. To put it simply, the distinction between mass and count is one between stuff and things.

You can usually guess whether a noun will be of the mass or count variety from its meaning, but what ultimately determines whether a word is classified as a mass noun or count noun is the way it functions grammatically.

Mass nouns are always singular, so like singular count nouns, they trigger singular agreement. Mass nouns also have something in common with plural count nouns because continuous substances and groups of countable objects can both vary in quantity. These factors partly explain which determiners you can use with mass nouns and how they compare with the determiners you can use with singular and plural count nouns:

In English, you can often force a mass noun interpretation of what is normally a count noun, or a count noun interpretation of what is normally a mass noun by using a different determiner or by switching between singular and plural forms:

I would like a cake. [singular count noun]
I would like some cake. [mass noun interpreted as cake substance]
I would like some cakes. [plural count noun]

I would like a water. [singular count noun interpreted as a glass or bottle of water]
I would like some water. [mass noun]
I would like some waters. [plural count noun interpreted as glasses or bottles of water]

The trick is to understand when it is appropriate to switch between mass and count interpretations. In English, hair is treated like a mass noun when we speak of the stuff that grows on our heads but a count noun when speaking of individual strands:

INCORRECT: I need to brush my hairs. [count noun]
CORRECT: I need to brush my hair. [mass noun]
CORRECT: There is a hair on my pizza! [count noun]

Another source of confusion for people learning English is the word news which looks like a plural count noun because of the -s ending, but is actually a mass noun:

INCORRECT: I have a good new for you. [count noun]
CORRECT: I have some good news for you. [mass noun]