In English, a mass noun is a type of noun that cannot be modified by a number without specifying a unit of measurement; thus mass nouns have singular but no plural forms. Contrast this with count nouns, which denote "things". A noun phrase can refer to one or more of these things. A mass noun denotes stuff, or a substance. Stuff, unlike things, is considered to be "divisible". One speaks of removing some stuff from, say, a container. One does not normally speak of a stuff.

Some illustrative examples of English mass nouns:

• water
• furniture
• meat
• knowledge
• software

Some nouns can have both mass noun and count noun meanings. For example, "laundry" as a mass noun is the stuff you put in the washing machine, i.e. dirty clothes. A "laundry" as a count noun is an establishment which washes clothes, also known as a laundromat or laundrette. The difference in meaning can be interpreted from whether the item is counted:

"There is laundry on my street." (must be a mass noun)

"There is a laundry on my street." (must be a count noun)

This difference is subtle when phrased in the negative:

"There is no laundry on campus." (could be either)

"There are no laundries on campus." (must be a count noun)

Another marker of difference between mass and count nouns is "less" and "fewer":

We have less furniture.

We have fewer chairs.

Many English speakers use "less" for both types; in the 1990s several British supermarkets were criticised for their signs above checkouts reading "10 items or less". The proper form is "10 items or fewer": "items" is a count noun, and a mass noun cannot be given a number anyway. In American English, "less" is used more commonly than "fewer" to describe count nouns, although this usage is still considered incorrect.

A mass noun can be preceded by a count noun, as in "ten pieces of furniture" or "a gallon of water".

Note that the lack of a distinct plural form is not a sufficient criterion by itself to say that a noun is a mass noun. For example, the singular and plural forms of the word "deer" are identical, but it is gramatically acceptable to say "three deer", "a deer", or "several deer". Therefore, "deer" is a count noun. Compare with "rice": not only is there no plural "rices", but "three rice", "a rice", and "several rice" all appear wrong to native English speakers.

The word "data" is often used as a mass noun, especially by people who work with computers. In formal writing it retains its original grammatical role as the plural of "datum".

There is a certain tendency in colloquial American English to treat some mass nouns as countable, e.g. "softwares" for "software", "behaviors" for "behavior", "accommodations" for "accommodation". One could argue that these countable forms have slightly different meanings than their mass forms.

Aquafina and Ozarka are two different brands of water.

Aquafina and Ozarka are two different waters.

Some kinds of nouns have subtle rules. For example count forms are used for fish not intended for food while mass nouns are used for fish one would eat.

The net is full of salmon.

The net is full of sharks. (If the speaker is not a shark eater.)

The net is full of shark. (If the speaker is a shark eater.)

See also

• English grammar
• Collective noun