Ways to understand Indefinite Articles
A, AN
1. The twenty-six letters of the alphabet of the English language are divided into vowels and consonants. 'A' is used with nouns starting with a consonant (letters that are not vowels) and 'an' is used when the noun begins with a vowel (a,e,i,o,u).
Examples: A bat
An orange
A bike
An ape
*Exception: The usage of 'a' or 'an' also depends on the sound of the words.
For Example: An hour
Although the letter 'h' is a consonant, we use the article 'an' because the consonant 'h' is silent.
2. Use A or An to refer to something that is being used for the first time.
Example: A
boy and a girl went to the
movies. The boy bought a drink and
the girl bought some popcorn.
3. The indefinite articles are used to refer to an individual member of a group or class.
Example: Katy wants to be a
teacher.
Heather is a Methodist.
Angie plays a saxophone.
http://www.edufind.com/english/grammar/Determiners3.cfm
