But you don't have to explicitly tell a human what the reward function for Pac-Man is. Show a human the game and they'll figure it out. Which makes me wonder if, while there is some room for variability in reward functions, there might be some basic underlying reward computation that is inherent in intelligence. I can't find the link just now, but I read an article a few months ago (might've even been here on HN) about a system that demonstrated the appearance of intelligent behavior by trying to minimize entropy and maximize its possible choices for as long as possible within a given world model.