§ 49. Science, then, is to be understood as springing from the practical necessity of anticipating the environment. This anticipation appears first as congenital or acquired reactions on the part of the organism. Such reactions imply a fixed coördination or system in the environment whereby a given circumstance determines other circumstances; and science proper arises as the formulation of such systems. The requirement that they shall apply to the phenomena that _confront_ the will, determines their spacial, temporal, and quantitative form. The progress of science is marked by the growth of these conceptions in the direction of comprehensiveness on the one hand, and of refinement and delicacy on the other. Man lives in an environment that is growing at the same time richer and more extended, but with a compensatory simplification in the ever closer systematization of scientific conceptions under the form of the order of nature. [Sidenote: The Determination of the Limits of Natural Science.] § 50. At the opening of this chapter it was maintained that it is a function of philosophy to criticise science through its generating problem, or its self-imposed task viewed as determining its province and selecting its categories. The above account of the origin and method of science must suffice as a definition of its generating problem, and afford the basis of our answer to the question of its limits. Enough has been said to make it clear that philosophy is not in the field of science, and is therefore not entitled to contest its result in detail or even to take sides within the province of its special problems. Furthermore, philosophy should not aim to restrain science by the imposition of external barriers. Whatever may be said of the sufficiency of its categories in any region of the world, that body of truth of which mathematics, mechanics, and physics are the foundations, must be regarded as a whole that tends to be all-comprehensive in its own terms. There remains for philosophy, then, the critical examination of these terms, and the appraisal as a whole of the truth that they may express. [Sidenote: Natural Science is Abstract.]