The Articles

The Articles

The three articles — a, an, the — are a kind of adjective. 

The is called the definite article because it usually precedes a specific or previously mentioned noun.

a and an are called indefinite articles because they are used to refer to something in a less specific manner (an unspecified count noun). 

A, an and the are also listed among the noun markers or determiners because they are almost invariably followed by a noun (or something else acting as a noun).

To make it clear See the table bellow! 

	singular	plural	definite	indefinite
a	√	-	-	√
an	√	-	-	√
the	√	√	√	-

We use a before singular count-nouns that begin with consonants (a cow, a barn, a sheep).
 we use an before singular count-nouns that begin with vowels or vowel-like sounds (an apple, an urban blight, an open door). 

Words that begin with an h sound often require an a (as in a horse, a history book, a hotel), but if an h-word begins with an actual vowel sound, use an an (as in an hour, an honor). 

We would say a useful device and a union matter because the u of those words actually sounds like yoo (as opposed, say, to the u of an ugly incident). 

The same is true of a European and a Euro (because of that consonantal "Yoo" sound). 

We would say a once-in-a-lifetime experience or a one-time hero because the words once and one begin with a w sound (as if they were spelled wuntz and won).