The word an is the prevocalic form of the word a.

He didn't take an academic course, but picked up the subject autodidactically.

As she tied the boxes, her curiosity could no longer be contained. Mister, she said, for why do you need such hats?

Lost in the middle of nowhere, he started to fix it by using his car-jack as a bead breaker, using the weight of the car to gently separate the bead from the rim.