And my hypothesis for what's going on here is that basically you as a creature with a very complex set of hazards and opportunities in your life use nighttime when you're not doing productive work to get ahead on challenges that you may face in one way or another. Sometimes those challenges are warnings about defects you know in yourself that might put you in a bad situation, like if you're a procrastinator and you're in school, you may have nightmares about showing up to the exam without having attended class or something that kind of gets you focused. Or they can be other kinds of practice. They can be philosophical practice. They can be situations in which you might be morally compromised where you need to go through the experience of being faced with a choice where you really should choose A, but B is very appealing or something. So I would say scenario building, that your mind is running you through little movies that it makes. They're not completely rendered because it would be too expensive and pointless to do so. But the central elements, the important stuff is there for you to have the experience so that when you do run up against a situation that's analogous, you've practiced it a number of times and you're not starting from scratch.

Dreaming is generally the brain making use of what it knows about how to construct the world in the waking state and doing so in the dream state. So that's why if you ask people, you know, many studies on dreaming have shown that people, when they dream, they dream about people, they dream about dogs and cats, they dream about, you know, that the amount of time they spend talking on the telephone or watching TV is actually similar to what it is in waking life. So dreaming is more like a selective simulation of the waking world.