The article is a form word that serves as a noun determiner. It is one of the main means of conveying the idea of definiteness and indefiniteness.
There are two articles in English: the definite article the [ði:] and the indefinite article a [ei].
Definiteness suggests that the object presented by the following noun is individualized and singled out from all the other objects of the same kind, whereas indefiniteness means a more general reference to an object.
Thus when saying The book is a historical novel or The boy has a dog the speaker characterizes the objects in a more general way, pointing out what kind of novel the book is and what kind of pet animal the boy has.
The notion of definiteness/indefiniteness determines the important role of the article in the process of communication. The definite article usually presents the notion as something already known, whereas the indefinite article introduces a new item of information.
Since the article is a noun determiner and the noun is the headword in a noun phrase, the syntactical role of the article consists in marking off a noun or a noun phrase as part of the sentence.
The morphological value of the article lies in indicating the substantivization of other parts of speech, mainly adjectives or participles, also pronouns, adverbs, numerals
Her hair was a bright brown.
It wasn’t a he.
He is such a nothing.
Both articles have originated from notional parts of speech, whose influence may be traced in their meaning and use.
The definite article developed from a demonstrative pronoun, which accounts for its meaning of definiteness.
The indefinite article developed from the cardinal numeral one/
Since the article is the opening element of a noun phrase, it is placed before the noun it refers to or before all the other noun premodifiers. The exceptions to this rule are as follows:
a) the definite article may be preceded by the predeterminers all and both:
Both the answers were good.
b) the indefinite article may be preceded by the predeterminers what, such, quite:
You were such a queen, and I was such a nothing!
с) the indefinite article is placed after adjectives preceded by the adverbs too, as, so:
That was too difficult a problem for the child to solve.