What if there really ARE only two kinds of people?

"What if heredity instead of linear, is branching? What if in fact there were ever only like two really distinct individual people walking around back there in history's mist? That all difference descends from this difference? The whole and the partial. The damaged and the intact. The deformed and the paralyzingly beautiful. The insane and the attendant. The hidden and the blindingly open. The performer and the audience. No Zen-type One, always rather Two, one upside down in a convex lens."

-- David Foster Wallace, Infinite Jest, page 220.