Similar to Pass the Potatoes- in a shorter version:
http://wondertime.go.com/parent-to-parent/article/why-kids-should-talk-back.html

My 6 year old is very stubborn, very logical and very much a lawyer at heart. He will argue until the cows come home if he thinks your point has no merit. There has never been "because I said so" in my house because it would have only increased the argument.

We have "Team ___" (our last name)rules. If you want to be on the team, you have to follow the rules. If you don't, you go to the penalty box for a time to be determined by the referee (me). We have all taken our time in the penalty box in the last 6 years! If you would like to discuss a rule change, you must do it when the rule has NOT been violated.

I worry about ever giving him the impression that adults are always right, that he must do what I say or that you can't ask "why am I doing this?" He knows there is a tone in my voice, reserved for emergencies, that means JUMP NOW ASK LATER. But I want him to learn to question and understand WHY it's good, not just believe it's good because I said so.