Most languages have ways to express differences of number.
- That apple on the table is fresh.
- Those two apples on the table are fresh.
Some languages (like Chinese) do not have the concept of grammatical number, and numbers or other quantifiers are used if necessary. Finally, there may be words that have only one form or are not countable.
- Greenberg, Joseph H 1972. Numeral classifiers and substantival number: problems in the genesis of a linguistic type. Working Papers on Language Universals 9, Stanford University, pp. 1–39.
- Laycock, Henry 2005. Mass nouns, count nouns and non-count nouns. Encyclopedia of Language and Linguistics. Oxford: Elsevier.
- "What is Number?", Dictionary of Linguistic Terms, SIL.