an is used before feminine words beginning with a vowel (a, e, i, o, and u).

It is a theory of the Government and Binding framework and its successors. There are two Cases that are generally recognized in English--the nominative Case and the accusative Case--the latter is also ...

In English, the definite article the is the same whether it used for a singular or a plural noun. In Gaelic, however, when the noun is plural the definite article changes to na or na h-.