In general, the zero article is used with proper nouns, mass nouns where the reference is indefinite, and plural count nouns where the reference is indefinite. Also, the zero article is generally used with means of transport ("by plane") and common expressions of time and place ("at midnight," "in jail").
Examples and Observations:
- "Every mile is two in winter."
- This plant grows in sandy soil and on the edges of swamps.
- David Rockefeller was authorized to hold the position of director of the Council on Foreign Relations.
- "If we were to wake up some morning and find that everyone was the same race, creed and color, we would find some other cause for prejudice by noon."
- "If you meet at dinner a man who has spent his life in educating himself you rise from the table richer."
- Zero Article in American English and British English
Zero article . . . is also used with school, college, class, prison and camp when these are used in their 'institutional' sense. . . . [C]ertain nouns that are never used with zero article in American English do occur with zero article in British English when used in their institutional sense: hospital, university, and government."
(Ron Cowan, The Teacher's Grammar of English. Cambridge Univ. Press, 2008)
When I was in the hospital, I often wished there were more hours in a day and more days in a week. [American]
When Elizabeth was in hospital, she had the occasional visit from her parents and one visit from her brother.
- Zero Article with Plural Count Nouns and with Mass Nouns
The loosest and therefore most frequent type of generic statement is that expressed by the zero article with plural count nouns or with mass nouns:
- Kangaroos are common in Australia.
- Wine is one of this country's major exports.
- Frogs have long hind legs. (generic = all frogs)
- He catches frogs. (indefinite = an indefinite number of frogs)
(Angela Downing, English Grammar. Routledge, 2006)