The conception of an end is forced upon us in considering life, because then it is necessary to take account of the being as organised, and therefore as a whole. In the investigation of nature, on the other hand, things may be apprehended without relation to the conception of the whole; and teleology, therefore, seems to be unnecessary. The notion of purpose, it is often said, is essential to biology, but out of place in physical science. But when we look on the world as a whole, the notion of end or purpose is introduced, and the functions of its various parts conceived from a new point of view. And the end of an organism can only be partially understood, when that organism is conceived as a whole apart from its environment. It is only a partial manifestation or example of the more perfect reality in which things are to be regarded as not merely conditioned and conditioning, but as revelations of purpose. But, although the notion of purpose cannot be dispensed with in considering organic nature, the teleological notions we form of living things are imperfect and "abstract." Thus the organism is often, more or less explicitly, judged by its utility for some human purpose. In these cases the end is clearly an external and dependent one. And, when the adaptation of its parts is spoken of in relation to its type or perfect form, a conception is involved over and above what can be inferred from the nature of the organism in itself. The notion of the end depends upon a rational ideal, which passes beyond the causal interrelation of parts to the conception of the organism as a whole, whose function is necessarily related to its environment. [Sidenote: and life directly known only as self-conscious.]