As quoted on the Screenwriting from Iowa blog, Aaron Sorkin talked in the Creative Screenwriting podcast about theme:
“When you’re talking about things like theme you have to be really careful because that’s not what’s going to make the car go. Okay? It’s what’s going to be what makes the car be good and give you a good ride. But that’s not what’s going to make the car go—at least not for me. You know, everybody writes different. But for me I have to stick—really closely, like it’s a life raft— to intention and obstacles. Just the basics of somebody wants something, something is standing in their way of getting it. Make sure you have that cemented in place. Themes will then become apparent to you and you can hang a lantern on the ones you like. Bring them into relief, you can get rid of the ones that aren’t doing you any good and you can paint the car and make it look really nice. But the car isn’t going to turn over unless you see to the basics of drama, and drama is intention and obstacles, somebody wants something, something is standing in their way of getting it.”
You can hear the interview here:
Creative Screenwriting podcast interview by Jeff Goldsmith