It's been too long...

A man gives his son an electric bass for his 15th birthday, along with a coupon for four bass lessons. When the son returns from his first lesson, the father asks, "So, what did you learn?"
"Well, I learned the first five notes on the E string." Next week, after the second lesson, the father again asks about the progress, and the son replies, "This time I learned the first five notes on the A string."
One week later, the son comes home far later than expected, smelling of cigarettes and beer. So the father asks: "Hey, what happened in today's lesson?"
"Dad, I'm sorry I couldn't make it to my lesson; I had a gig!"