A proper noun is a noun that picks out a unique entity. This sets proper nouns apart from common nouns, which pick out classes of entities. Examples of proper nouns include: A noun, or noun substantive, is a part of speech which can co-occur with (in)definite articles and attributive adjectives, and function as the head of a noun phrase. ... A noun, or noun substantive, is a word or phrase that refers to a person, place, thing, event, substance or quality. ...

1. Joel

2. the CSI

3. Paris

and examples of common nouns are:

1. man

2. organization

3. country

Proper nouns also differ from common nouns in not being able to co-occur with other expressions that common nouns can co-occur with. For example, in English, proper nouns normally can't be preceded by (in-)definite articles. This makes it seem that proper nouns behave as though they are full noun phrases. In other languages, like Spanish, proper nouns do, in fact, regularly co-occur with definite articles. Even in English, there are examples of proper nouns preceded by articles, as in the example 2. below. However, one could argue that, in this case, `Paris' is used as a common noun, rather than as a proper noun. This does not cite its references or sources. ... In linguistics, a noun phrase is a phrase whose Head is a noun. ...

1. The John is smart. (incorrect)

2. This is very much like the Paris of my youth. (correct)