The indefinite article
The article a (an before a vowel—an apple, an ear, an Italian, an orange, an umbrella)
means one, without emphasis. Therefore, it can be used only with countable nouns:
man turned on
book on US social policy.
No specific light, apple, or book is identified.
can not be used with non-count nouns such as
water, equipment, information
, nor with a
noun that has already been defined (through previous mention).
is usually used with
singular count nouns that are not definite, identified, or limited in number:
Because it means "one,"
has no plural. Sometimes no article or adjective is used with
indefinite plural nouns:
Do you have books on US social policy?
At other times, the words
I don't have
The definite article
Once the indefinite noun has been introduced, it is afterward referred to as
experiment, the participant, etc.):
man turned on a light.
man, John Smith, then sat down.
This is also true with plural nouns and, usually, with non-count nouns:
on recombinant DNA. The results of
has reached us from the battlefield, and
news is not good.
However, persons and unique things or ideas are defined by their names. They will take
either no article (usually, names of people, cities, continents, countries, lakes, parks, streets)
(buildings, geographical regions, oceans, rivers, seas):
Empire State Building,