Non-Countable Nouns
A non-countable noun (or mass noun) is a noun which does not have a plural form, and which refers to something that you could (or would) not usually count. A non-countable noun always takes a singular verb in a sentence. Non-countable nouns are similar to collective nouns, and are the opposite of countable nouns.
The highlighted words in the following sentences are non-countable nouns:
Joseph Priestly discovered oxygen.
The word "oxygen" cannot normally be made plural.
Oxygen is essential to human life.
Since "oxygen" is a non-countable noun, it takes the singular verb "is" rather than the plural verb "are."
We decided to sell the furniture rather than take it with us when we moved.
You cannot make the noun "furniture" plural.
The furniture is heaped in the middle of the room.
Since "furniture" is a non-countable noun, it takes a singular verb, "is heaped."
The crew spread the gravel over the roadbed.
You cannot make the non-countable noun "gravel" plural.
Gravel is more expensive than I thought.
Since "gravel" is a non-countable noun, it takes the singular verb form "is."
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