But in order to regard a thing cognised as a natural product as a purpose also--consequently as a _natural purpose_, if this is not a contradiction--something more is required. I would say provisionally: a thing exists as a natural purpose, if it is [although in a double sense][107] 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. Secondly, a tree produces itself as an _individual_. This kind of effect no doubt we call growth; but it is quite different from any increase according to mechanical laws, and is to be reckoned as generation, though under another name. The matter that the tree incorporates it previously works up into a specifically peculiar quality, which natural mechanism external to it cannot supply; and thus it develops itself by aid of a material which, as compounded, is its own product. No doubt, as regards the constituents got from nature without, it must only be regarded as an educt; but yet in the separation and recombination of this raw material we see such an originality in the separating and formative faculty of this kind of natural being, as is infinitely beyond the reach of art, if the attempt is made to reconstruct such vegetable products out of elements obtained by their dissection or material supplied by nature for their sustenance.