A complete and satisfactory interpretation of nature, is so far as it is attainable by man, partly scientific and partly metaphysical. It has been my object to distinguish these factors. The departmental studies such as physics and biology are founded on our perceptions in their objective aspect, having a correspondence of reference for independent observers, and afford explanations in terms of antecedence and sequence in a doctrine of scientific causation. They deal with the observed moves among the pieces on the checkered chess-board of experience, leaving to metaphysics the question how there comes to be a game to be played, and when this is settled how, or by what unseen agency, castles and knights and pawns are moved, each with a distinctive path across the board.
But the perceptions and all the varied data of presentational experience not only have an objective reference with which such sciences as astronomy, geology, biology, and the more analytical studies of physics and chemistry are concerned, they are also states of consciousness. And these states of consciousness follow each other in orderly, or at any rate for science determinate sequence. The data of mental science no less than the data of physical science are provided in and through experience. The inner or subjective state of consciousness which we call the perceiving of an object is every whit as much a reality of experience as the external reference to the object of perception. Indeed, they are integral parts of the same experience regarded from different points of view. In the one case the reference is outward to the object, in the other case it is inward to the subject. The science of psychology (apart from the metaphysics of the subject) deals with the concatenation of items of experience from this latter, that is, the subjective point of view. It is concerned with antecedence and sequence as they obtain among states of consciousness—that is to say, as they are observed to occur apart from any consideration of causal activity in the metaphysical sense.
But it may be urged that in its subjective aspect experience is a purely individual matter. It is mine or yours or another man's as a wholly private posses sion. I cannot get at your states of consciousness, neither can you get at mine. How under these conditions can we possibly elaborate a scheme of scientific interpretation? How can we obtain materials for anything like an ideal construction of social validity?
I return to the illustrative example of a rose-bud and half a dozen people. Each has a perception of the flower, and, just in so far as this is a purely private and individual experience of the passing moment, it is subjective. It is something that wholly concerns his own state of consciousness; but in so far as that self-same perception has a reference which corresponds to the like references of the other five persons, it is objective. There is, however, a different kind of reference on which, as a matter of experience, we guide our actions in our intercourse with our fellow-men. This reference is to a subjective aspect of our neighbour's perceptions analogous to that which is for us a purely private and individual matter. It is true that no one of us can have direct and first-hand acquaintance with the states of consciousness of any other being; but it is also true that no one of us can have such acquaintance with another man's object of perception. In the latter case we assume a corresponding reference which is amply justified throughout the whole of our social intercourse. So, too, in the former case we assume corresponding states of consciousness. To employ Clifford's phrase, we endow our neighbours with "ejects" that is to say, independent centres of corresponding subjective reference. This forms part of the ideal construction of psychology, which is thus, and only thus, raised to the level of a science with opportunities for comparative study. Mental science thus deals with the antecedences and sequences which obtain among ejective states of consciousness having correspondence of social reference.
I desire now to render clear the naturalistic method of interpretation within the strictly psychological field of inquiry. We have seen that physics as a science, setting aside all conceptions of causal agency, deals with its phenomena in terms of configuration. It says, Given such and such a configuration, these specific movements will be found to occur, if experience in the past is a trustworthy guide to experience in the future. So, too, does naturalistic psychology deal with configuration of items of experience in their subjective aspect. It too says, Given such and such a thought-configuration, these specific movements in the field of consciousness will occur. It too excludes all conceptions of causal agency, dealing simply with the facts of mental sequence.
Now obviously this is a piece of ideal construction. It is at present quite impossible to evaluate what may be termed the accelerations in consciousness. The most we can say is that, as a matter of naturalistic belief, if we knew all the items which constitute a psychological disposition, and if we could assign to each a numerical coefficient, and if we could also assign values to the accelerations which fall under the categories of association, interest, and so forth, then we could foretell the exact manner in which the mental configuration would change. In point of fact we can do nothing of the sort. Nevertheless, this may be the ideal goal towards which psychology is working with only limited powers of realising its ideal. Let that pass, however. Grant the naturalistic assumptions, and see how such a psychology deals with the phenomena of volition. I say "phenomena of volition" advisedly, since it is only of phenomena within the conscious configuration that such a psychology takes cognisance. We must remember that the field of conscious experience is only a minor configuration (where the doctrine of concomitance holds good) within a wider physical and physiological configuration. On these terms we can accept presentations from the wider configuration of the world around us within the narrower configuration of our own private experience.