Countable nouns name things that can be counted and have singular and plural forms (a book / two books); uncountable (mass) nouns name substances, abstractions, or aggregates seen as undivided wholes, take no plural, and take no a/an (water, information, advice). Countability is a grammatical property of how a noun is used, not a fact about the world, which is why the same word can switch classes.
Countability governs the rest of the Noun Phrase: which determiners and articles are allowed, whether the noun can be plural, and which quantifiers fit.
| Feature | Countable | Uncountable |
|---|---|---|
| Plural form | yes (chairs) | no (furniture) |
| a / an | yes (a chair) | no (not an information) |
| many / few | many chairs, few chairs | n/a |
| much / little | n/a | much furniture, little furniture |
| some / any | with plural (some chairs) | with singular (some furniture) |
So much/many and (a) few/(a) little split along the count line, while some and any work with both.
To count an uncountable noun, English uses a partitive: a counting unit plus of: a piece of advice, a slice of bread, a bar of soap, two litres of water, a bit of luck. These let speakers individuate mass nouns without making them grammatically plural.
Many nouns are countable in one sense and uncountable in another, with a clear meaning shift:
A small set of nouns is uncountable in English but countable in many other languages, producing persistent errors (an information, advices, furnitures, a news). The high-frequency offenders are information, advice, furniture, news, equipment, luggage, accommodation, knowledge, and research. These need explicit treatment and the partitive workaround (a piece of news).