djectives qualified by too, so, as and how generally precede the indefinite article: too great a loss, so hard a problem, as delicious an apple as I have ever tasted, I know how pretty a girl she is. When adjectives are qualified by quite (particularly when it means "fairly"), the word quite (but not the adjective itself) often precedes the indefinite article: quite a long letter.
The definite article the is the default when the referent of the noun phrase headed by a common noun is assumed to be unique or known from the context. For example, In the sentence The boy with glasses was looking at the moon, it is assumed that in the context the reference can only be to one boy and one moon. However, the definite article is not typically used:
The articles in English are the definite article the and the indefinite articles a and an. They are the two most common determiners. The definite article is the default determiner when the speaker believes that the listener knows the identity of a common noun's referent (because it is obvious, because it is common knowledge, or because it was mentioned in the same sentence or an earlier sentence). The indefinite article is the default determiner for other singular, countable, common nouns, while no determiner is the default for other common nouns. Other determiners are used to add semantic information such as amount (many, a few), proximity (this, those), or possession (my, the government's).