Articles are words used with nouns to indicate definiteness or indefiniteness. There are three articles: indefinite articles "a" and "an", and the definite article "the". The indefinite articles refer to nonspecific or unknown nouns, while the definite article refers to specific nouns. The choice between "a" and "an" depends on whether the following word begins with a vowel or consonant sound. The definite article "the" is used to talk about a particular noun. In some cases no article is needed, such as with plural uncountable nouns.