an—used before singular count nouns beginning with a vowel (a, e, i, o, u) or vowel sound:
an apple, an elephant, an issue, an orange
a—used before singular count nouns beginning with consonants (other than a, e, i, o, u):
a stamp, a desk, a TV, a cup, a book
Can be used before singular and plural, count and non-count nouns
1. Indefinite Article (a, an)
Used before singular nouns that are unspecified:
Used before number collectives and some numbers:
Used before a singular noun followed by a restrictive modifier:
a girl who was wearing a yellow hat
Used with nouns to form adverbial phrases of quantity, amount, or degree:
I felt a bit depressed.
2. Definite Article (the)
Used to indicate a noun that is definite or has been previously specified in the context:
Please close the door.
I like the clothes you gave me.
Used to indicate a noun that is unique:
Praise the Lord!
The Columbia River is near here.
Used to designate a natural phenomenon:
The nights get shorter in the summer.
The wind is blowing so hard.
Used to refer to a time period:
I was very naïve in the past.
This song was very popular in the 1980s.
Used to indicate all the members of a family:
I invited the Bakers for dinner.
This medicine was invented by the Smiths.