An ecological understanding allows us to identify "things"—rain, cloud, river—at the same time that it reminds us that these identities are fluid. Even mountains erode, and the ground below us moves in giant plates. It reminds us that—while it's useful to have a word for that thing called a cloud—when we really get down to it, all we can really point to is a series of flows and relationships that sometimes intersect and hold together long enough to be a "cloud."