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Indefinite & definite articles in English
1. The Definite Article
How simple English is !! There is only one definite article, and that is "the"; the only difficulty is
knowing when to use it, and when it is not needed.
Use of the definite article depends on the nature or type of noun that is being used.
As in other languages, nouns in English can be divided into two distinct categories, called: count
nouns and non-count nouns.
► Count nouns are nouns referring to items that can be counted, for example:
One car, two pencils, three people, four guitarists, five hotels etc.
These nouns can be used in the singular or the plural
In the singular, count nouns must
The dog is happy. (or This dog is happy, etc: but not: Dog is happy )
I'm reading the book you gave me.
In the plural, they may require a determiner, depending on context.
►Non-count nouns are nouns referring to abstractions, substances or generalizations, or
example:
Oxygen, health, money, heat, astronomy
In the singular, non-count nouns do not require a determiner.
They can NOT usually be used in the plural.
For more detail see Count & non-count nouns
THE
BIG QUESTION concerns plural nouns:
Generalisation or not?
Sometimes it is not easy to decide if a plural noun is being used as a generalization, or in a
restrictive context : often the speaker or writer can choose. Look at these two sentences:
a) London buses are red
b) The London buses are red.
In example (a), the writer is clearly implying a generalisation on the noun group
"London buses": All London buses are red.
In example (b), he is referring to a restricted or defined category of the noun:
"buses", London buses are red, but other buses may be of other colours.
In cases like these, one therefore has a choice; but the choice is not always completely free, as it
often depends on context. Is it more important or more logical to imply a generalization, or a
limitation?
Deciding whether it is best to use an article in such cases is a skill that has to be mastered!
http://linguapress.com/grammar/article-in-english.htm
2. The Indefinite Article
English has two indefinite articles, a and an
a is used before nouns starting with a consonant or a semivowel
an is used before nouns starting with a phonetic vowel
Examples: a dog, a cat, an apple, an orange, an uncle, but a university (because the
word university starts with phonetic [ju], which is not a vowel).
Indefinite articles can only be used with count nouns. They are used when a count noun in the
singular refers to a non-specified or non defined entity.
Examples:
a) There's a train (= unspecified) coming in 5 minutes. It's the train (= specified) for London.
b) Look! I can see an elephant over there ! (= a non-identified elephant)
There is no indefinite article in the plural. The word "some" is occasionally said to be a plural
indefinite article, but really it is a quantifier (like many, few, etc.)
By definition, plural nouns refering to non-specified entities are generalisations, therefore need no
article.