Another example of a binary category that's nowhere near as binary as we'd like it to be: "alive" and "dead". To start with, we've got the question of whether "non-living" and "dead" are different categories -- is a rock dead, or is "not alive" something different? What about a pearl? Or abalone shell jewelry? Teeth for the tooth fairy? A house made of wood?

Then we've got things that have SOME characteristics that we associate with life, but not others: viruses -- alive or not? Computer viruses -- alive or not?

And then we get into medical ethics: at what point is a PERSON dead? There's no bright line.