proper

A proper noun is a noun that identifies a single entity and is used to refer to that entity (Africa; Jupiter; Sarah; Toyota) as distinguished from a common noun, which is a noun that refers to a class of entities (continent, planet, person, corporation) and may be used when referring to instances of a specific class (a continent, another planet, these persons, our corporation). Some proper nouns occur in plural form (optionally or exclusively), and then they refer to groups of entities considered as unique (the Hendersons, the Everglades, the Azores, the Pleiades). Proper nouns can also occur in secondary applications, for example modifying nouns (the Mozart experience; his Azores adventure), or in the role of common nouns (he's no Pavarotti; a few would-be Napoleons). The detailed definition of the term is problematic and, to an extent, governed by convention.
A distinction is normally made in current linguistics between proper nouns and proper names. By this strict distinction, because the term noun is used for a class of single words (tree, beauty), only single-word proper names are proper nouns: Peter and Africa are both proper names and proper nouns; but Peter the Great and South Africa, while they are proper names, are not proper nouns. The term common name is not much used to contrast with proper name, but some linguists have used it for that purpose. While proper names are sometimes called simply names, this term is often used more broadly: "An earlier name for tungsten was wolfram." Words derived from proper names are occasionally called proper adjectives (or proper adverbs, and so on), but not in mainstream linguistic theory. Not every noun phrase that refers to a unique entity is a proper name. For example, chastity is a common noun even though chastity is considered a unique abstract entity (constrasted with the personal name Chastity, which is a proper name).
Few proper names have only one possible referent: there are many places named New Haven; Jupiter may refer to a planet, a god, a ship, a city in Florida, or as part of the name of a symphony ("the Jupiter Symphony"); at least one person has been named Mata Hari, as well as a racehorse, several songs, several films, and other objects; there are towns and people named Toyota, as well as the company. In English, proper names in their primary application cannot normally be modified by articles or another determiner, although some may be taken to include the article the, as in the Netherlands, the Roaring Forties, or the Rolling Stones. A proper name may appear to have a descriptive meaning, even though it does not (the Rolling Stones are not stones and do not roll; a woman named Rose is not a flower). If it once had a descriptive meaning, it may no longer be descriptive; a location previously referred to as "the new town" may now have the proper name Newtown though it is no longer new and is now a city rather than a town.
In English and many other languages, proper names and words derived from them are associated with capitalization, but the details are complex and vary from language to language (French lundi, Canada, un homme canadien, un Canadien; English Monday, Canada, a Canadian man, a Canadian; Italian lunedì, Canada, un uomo canadese, un canadese). The study of proper names is sometimes called onomastics or onomatology, while a rigorous analysis of the semantics of proper names is a matter for philosophy of language.
Occasionally, what would otherwise be regarded as a proper noun is used as a common noun, in which case a plural form and a determiner are possible. Examples are in cases of ellipsis (the three Kennedys = the three members of the Kennedy family) and metaphor (the new Gandhi, likening a person to Mahatma Gandhi).

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