Use of "a" and "an"

1. Use "a" in front ot a word that begins with consonant or "h" aspirated

2. "An" is used when the word that follows begins with a vowel or "h" changes

3. *a boy *a woman *a european *a spaniard *what a pity

4. *an doctor *an engenner *an italian *an irishman *half an hour