I would say provisionally: a thing exists as a natural purpose, if it is [although in a double sense] both cause and effect of itself. For herein lies a causality the like of which cannot be combined with the mere concept of a nature without attributing to it a purpose; it can certainly be thought without contradiction, but cannot be comprehended. We shall elucidate the determination of this Idea of a natural purpose by an example, before we analyse it completely.

In the first place, a tree generates another tree according to a known natural law. But the tree produced is of the same genus; and so it produces itself generically. On the one hand, as effect it is continually self-produced; on the other hand, as cause it continually produces itself, and so perpetuates itself generically.