The concept of a thing as in itself a natural purpose is therefore no constitutive concept of Understanding or of Reason, but it can serve as a regulative concept for the reflective Judgement, to guide our investigation about objects of this kind by a distant analogy with our own causality according to purposes generally, and in our meditations upon their ultimate ground. This latter use, however, is not in reference to the knowledge of nature or of its original ground, but rather to our own practical faculty of Reason, in analogy with which we considered the cause of that purposiveness. Organised beings are then the only beings in nature which, considered in themselves and apart from any relation to other things, can be thought as possible only as purposes of nature. Hence they first afford objective reality to the concept of a _purpose of nature_, as distinguished from a practical purpose; and so they give to the science of nature the basis for a teleology, _i.e._ a mode of judgement about natural Objects according to a special principle which otherwise we should in no way be justified in introducing (because we cannot see _a priori_ the possibility of this kind of causality). § 66. _Of the principle of judging of internal purposiveness in organised beings_ This principle, which is at the same time a definition, is as follows: _An organised product of nature is one in which every part is reciprocally purpose, [end] and means._ In it nothing is vain, without purpose, or to be ascribed to a blind mechanism of nature. This principle, as regards its occasion, is doubtless derived from experience, viz. from that methodised experience called observation; but on account of the universality and necessity which it ascribes to such purposiveness it cannot rest solely on empirical grounds, but must have at its basis an _a priori_ principle, although it be merely regulative and these purposes lie only in the idea of the judging [subject] and not in an effective cause. We may therefore describe the aforesaid principle as a _maxim_ for judging of the internal purposiveness of organised beings. It is an acknowledged fact that the dissectors of plants and animals, in order to investigate their structure and to find out the reasons, why and for what end such parts, such a disposition and combination of parts, and just such an internal form have been given them, assume as indisputably necessary the maxim that nothing in such a creature is _vain_; just as they lay down as the fundamental proposition of the universal science of nature, that _nothing_ happens _by chance_. In fact, they can as little free themselves from this teleological proposition as from the universal physical proposition; for as without the latter we should have no experience at all, so without the former we should have no guiding thread for the observation of a species of natural things which we have thought teleologically under the concept of natural purposes.