§ [117]. Holbach's "Système de la Nature," published in 1770, marks the culmination of the unequivocally materialistic form of naturalism. Its epistemological difficulties, always more or less in evidence, have since that day sufficed to discredit materialism, and to foster the growth of a critical and apologetic form of naturalism known as positivism or agnosticism. The modesty of this doctrine does not, it is true, strike very deep. For, although it disclaims knowledge of ultimate reality, it also forbids anyone else to have any. Knowledge, it affirms, can be of but one type, that which comprises the verifiable laws governing nature. All questions concerning first causes are futile, a stimulus only to excursions of fancy popularly mistaken for knowledge. The superior certainty and stability which attaches to natural science is to be permanently secured by the savant's steadfast refusal to be led away after the false gods of metaphysics.
But though this is sufficient ground for an agnostic policy, it does prove an agnostic theory. The latter has sprung from a closer analysis of knowledge, though it fails to make a very brave showing for thoroughness and consistency. The crucial point has already been brought within our view. The general principles of naturalism require that knowledge shall be reduced to sensations, or impressions of the environment upon the organism. But the environment and the sensations do not correspond. The environment is matter and motion, force and energy; the sensations are of motions, to be sure, but much more conspicuously of colors, sounds, odors, pleasures, and pains. Critically, this may be expressed by saying that since the larger part of sense-perception is so unmistakably subjective, and since all knowledge alike must be derived from this source, knowledge as a whole must be regarded as dealing only with appearances. There are at least three agnostic methods progressing from this point. All agree that the inner or essential reality is unfathomable. But, in the first place, those most close to the tradition of materialism maintain that the most significant appearances, the primary qualities, are those which compose a purely quantitative and corporeal world. The inner essence of things may at any rate be approached by a monism of matter or of energy. This theory is epistemological only to the extent of moderating its claims in the hope of lessening its responsibility. Another agnosticism places all sense qualities on a par, but would regard physics and psychology as complementary reports upon the two distinct series of phenomena in which the underlying reality expresses itself. This theory is epistemological to the extent of granting knowledge, viewed as perception, as good a standing in the universe as that which is accorded to its object. But such a dualism tends almost irresistibly to relapse into materialistic monism, because of the fundamental place of physical conceptions in the system of the sciences. Finally, in another and a more radical phase of agnosticism, we find an attempt to make full provision for the legitimate problems of epistemology. The only datum, the only existent accessible to knowledge, is said to be the sensation, or state of consciousness. In the words of Huxley:
"What, after all, do we know of this terrible 'matter' except as a name for the unknown and hypothetical cause of states of our own consciousness? And what do we know of that 'spirit' over whose threatened extinction by matter a great lamentation is arising, . . . except that it is also a name for an unknown and hypothetical cause, or condition, of states of consciousness?"[255:19]
The physical world is now to be regarded as a construction which does not assimilate to itself the content of sensations, but enables one to anticipate them. The sensation signifies a contact to which science can provide a key for practical guidance.
Experimentalism.
§ [118]. This last phase of naturalism is an attempt to state a pure and consistent experimentalism, a workable theory of the routine of sensations. But it commonly falls into the error of the vicious circle. The hypothetical cause of sensations is said to be matter. From this point of view the sensation is a complex, comprising elaborate physical and physiological processes. But these processes themselves, on the other hand, are said to be analyzable into sensations. Now two such methods of analysis cannot be equally ultimate. If all of reality is finally reducible to sensations, then the term sensation must be used in a new sense to connote a self-subsistent being, and can no longer refer merely to a function of certain physiological processes. The issue of this would be some form of idealism or of the experience-philosophy that is now coming so rapidly to the front.[256:20] But while it is true that idealism has sometimes been intended, and that a radically new philosophy of experience has sometimes been closely approached, those, nevertheless, who have developed experimentalism from the naturalistic stand-point have in reality achieved only a thinly disguised materialism. For the very ground of their agnosticism is materialistic.[256:21] Knowledge of reality itself is said to be unattainable, because knowledge, in order to come within the order of nature, must be regarded as reducible to sensation; and because sensation itself, when regarded as a part of nature, is only a physiological process, a special phenomenon, in no way qualified to be knowledge that is true of reality.
Naturalistic Epistemology not Systematic.
§ [119]. Perhaps, after all, it would be as fair to the spirit of naturalism to relieve it of responsibility for an epistemology. It has never thoroughly reckoned with this problem. It has deliberately selected from among the elements of experience, and been so highly constructive in its method as to forfeit its claim to pure empiricism; and, on the other hand, has, in this same selection of categories and in its insistence upon the test of experiment, fallen short of a thorough-going rationalism. While, on the one hand, it defines and constructs, it does so, on the other hand, within the field of perception and with constant reference to the test of perception. The explanation and justification of this procedure is to be found in the aim of natural science rather than in that of philosophy. It is this special interest, rather than the general problem of being, that determines the order of its categories. Naturalism as an account of reality is acceptable only so far as its success in satisfying specific demands obtains for it a certain logical immunity. These demands are unquestionably valid and fundamental, but they are not coextensive with the demand for truth. They coincide rather with the immediate practical need of a formulation of the spacial and temporal changes that confront the will. Hence naturalism is acceptable to common-sense as an account of what the every-day attitude to the environment treats as its object. Naturalism is common-sense about the "outer world," revised and brought up to date with the aid of the results of science. Its deepest spring is the organic instinct for the reality of the tangible, the vital recognition of the significance of that which is on the plane of interaction with the body.
General Ethical Stand-point.