From Glen Whitman: the Two Things.

A few years ago, I was chatting with a stranger in a bar. When I told him I was an economist, he said, “Ah. So… what are the Two Things about economics?”

“Huh?” I cleverly replied.

“You know, the Two Things. For every subject, there are really only two things you really need to know. Everything else is the application of those two things, or just not important.”

“Oh,” I said. “Okay, here are the Two Things about economics. One: Incentives matter. Two: There’s no such thing as a free lunch.”

Ever since that evening, I’ve been playing the Two Things game. Whenever I meet someone who belongs to a different profession (i.e., a profession I haven’t played this game with), or who knows something about a subject I'm unfamiliar with, I pose the Two Things question. (read the rest, including a long list of Two Things for various professions ...)

I don't normally quote so extensively, but i love how the Two Things game gets to the heart of what a field is all about. Even if you're not as clever as Glen's contributors (i'm not), it can really help to think at this most basic level.

My contribution -- The Two Things about Church:

1. The purpose of the church is to express God's love to humanity (including members of the church itself)
2. The church is like a body, with Christ as the Head