Indefinite Arcticle a/an

In order to differentiate the use of the indefinite article "a" or "an" you have to check if the following word starts by a vowel or a consonant. If the next word starts with a consonant, you have to use the article "a"and if the next word starts with a vowel you have to use the article "an". For example: my dad is an architect, my grandfather is a driver.