A and An
The choice of article is actually based upon the phonetic (sound) quality of the first letter in a word, not on the orthographic (written) representation of the letter.
Use "an" with words that start with a vowel sound.
Use "a" with words that start with a consonant sound.
*A Purple Onion
Hold up! You're not an expert at this yet.
An is used before an unsounded "h" This means that is the "h" is not heard in the word you use An instead of A.
*An honest error
*An honorable surrender
A is used when "u" makes the tame sound as the " y" in "you" and "o" makes the same sound as "w" in "won"
*A used napkin
*A U.S. flag
*A one-legged man