Unique reference occurs with proper names, i.e. the names of specific people, places, countries, months, days, holidays, magazines, etc.. These nouns are capitalized and in general do not take articles. For example:
Milton wrote Paradise Lost.
Sacramento is the capital of California.
July is the hottest month of the year.
I'm leaving next Thursday.
Playboy is published in several countries.
Where will you be at Easter?
Rule: Proper nouns usually take no article. Exceptions include plural names, rivers, seas, canals, public offices, institutions buildings, and documents.
Examples of errors:
Proper nouns are usually capitalized, though this is not very helpful to the learner unless he has seen the written form, and there are exceptions here as well. Structures consisting of a noun + cardinal number, based on article restrictions, are proper noun phrases, but are not always capitalized (cf. (2): sentence number 4 but Chapter 4, Article 4, etc.). Similarly, proper nouns like fate, paradise, nature, etc. are not necessarily capitalized.
Proper nouns are not the only nouns which can have unique reference, nor are they always more unique (i.e. less Ambiguous) in reference than ordinary common nouns. Robert is just as ambiguous as the train station, unless the situation of utterance makes it clear which Robert and which train station is meant. By the same token, both expressions are equally unique in reference when the context of discourse is clear. The question is when should an ordinary noun or noun phrase with unique reference be considered a proper noun? Why is subject part of a proper name in (2)-but a common noun in the equivalent expression the fourth subject? Why is station in 1.2.5 a common noun, but part of the proper name Grand Central Station? In the case of proper nouns translated into a second language, which of the various possible translations should be considered the proper noun equivalent of, for example, Frankfurt Hauptbahnhof: Frankfurt Train Station, Frankfurt Central Station, etc.? The superficial, and circular, answer of course is that the noun is a proper noun when no article is permitted, but what determines this? In some cases, the acquisition of proper name status may come about as a formal event, as when babies are born (or baptized) or when translations are officially approved. More generally, the transition from common to proper noun lies more obscurely in the history of the language--in convention.
Rule 1.3 applies to the category of plural names in general, including family names (the Smiths), islands (the Bahamas), mountain ranges (the Alps), countries (cf. (4)), historical periods (cf. (5)), etc. In earlier usage, and still today for some (particular British) speakers, United States takes a plural verb, though in American usage the name is construed as singular and takes a singular verb, still requiring the definite article.
Although the Rhineland (cf. (6)) is the name of a land area, not a river, the name obviously derives from the name of the river, and the article usage conforms to that for rivers in general. The same is true in the case of a name like the Sudetenland, which is also a land area, but derives from the name of a mountain range (the Sudetes). Note that seas, rivers and canals are all bodies of water, but lakes require the article. Here are some more examples:
rivers: the Fulda, the Rhine, the Thames, the Potomac
seas and oceans: the Pacific (Ocean), the Atlantic (Ocean), the Baltic (Sea), the Red Sea, the Persian Gulf, the Mediterranean (Sea), the Indian Ocean
canals: the Erie Canal, the Suez Canal, the Panama Canal
Most other (singular) geographical names obey the general rule in not taking an article (with some exceptions), e.g.:
continents: (North) America, Europe, Australia, Africa but the Anarctic,, the Artic
political divisions (countries, states, counties, towns): England, Brazil, France, Florida, Straffordshire, Pinellas County, St. Petersburg, London, (but the Argentine, the Bronx, The Hague.
lakes: Lake Michigan, Cayuga Lake
mountains: Mount Everest, Mount Vernon, Vesuvius buildings,
streets, bridges, parks: Rockefeller Center, Westminster Abbey, JFK Airport, Grand Central Station, Central Park, Fifth Avenue, Main Street, Drury Lane, London Bridge, but the United Nations (Building), the Strand, the Brooklyn Bridge, the Pennsylvania Turnpike.
Although the nouns in (7)-(9) are all foreign words, Rule 1.3 applies analogously to words like King, President, Prime Minister, Bible, Book of Kells, and University of London, all of which require the article. Names of universities (cf. (9) require the article only when the word university appears first (i.e. and is followed by an of phrase), so that we also have London University, Yale University, etc. Nouns in this category are capitalized, but it is not clear from a syntactic point of view what should distinguish them from ordinary common nouns with specific definite reference, since the definite article does occur, and most of these nouns can be used in the plural or with indefinite reference--i.e. as common nouns--as well (e.g. every president, many prime ministers, etc.). Furthermore, these nouns are capitalized or not according to the relative importance of the position or office within a particular organizational hierarchy. One writes the Secretary of State, for example, but the public relations officer, etc. Names of written documents do not present this problem, because they cannot double as common nouns: there is only one Koran, Book of Kells, etc. Bible, exceptionally, is occasionally used as a common noun, as in Marx's writings are the Communist bible.