But here these undisputed maxims pass over into problems opening out a wide field for difficulties. Does purposive connexion in nature _prove_ a particular kind of causality? Or is it not rather, considered in itself and in accordance with objective principles, similar to the mechanism of nature, resting on one and the same ground? Only, as this ground in many natural products is often hidden too deep for our investigation, we make trial of a subjective principle, that of art, _i.e._ of causality according to Ideas, and we ascribe it to nature by analogy. This expedient succeeds in many cases, but seems in some to mislead, and in no case does it justify us in introducing into natural science a particular kind of operation quite distinct from the causality according to the mere mechanical laws of nature. We give the name of _Technic_ to the procedure (the causality) of nature, on account of the appearance of purpose that we find in its products; and we shall divide this into _designed_ (_technica intentionalis_) and _undesigned_ (_technica naturalis_). The first is meant to signify that the productive faculty of nature according to final causes must be taken for a particular kind of causality; the second that it is at bottom quite similar to the mechanism of nature, and that its contingent agreement with our artistic concepts and their rules should be explained as a mere subjective condition of judging it, and not, falsely, as a particular kind of natural production. If we now speak of systems explanatory of nature in regard of final causes, it must be remarked that they all controvert each other dogmatically, _i.e._ as to objective principles of the possibility of things, whether there are causes which act designedly or whether they are quite without design. They do not dispute as to the subjective maxims, by which we merely judge of the causes of such purposive products. In this latter case _disparate_ principles could very well be unified; but in the former, contradictorily opposed laws annul each other and cannot subsist together. There are two sorts of systems as to the Technic of nature, _i.e._ its productive power in accordance with the rule of purposes; viz. _Idealism_ or _Realism_ of natural purposes. The first maintains that all purposiveness of nature is _undesigned_; the second that some (in organised beings) is _designed_. From this latter the hypothetical consequence can be deduced that the Technic of Nature, as concerns all its other products in reference to the whole of nature, is also designed, _i.e._ is a purpose.