With sufficient time and command of detail it would not be difficult to show how the conviction here illustrated, that whatever anything is really it is unalterably, regulates equally our most primitive and our most developed judgments of reality—the every-day supposition of there being a multitude of separate things which remain the same in themselves while their appearances to us alter, and the scientific quest for uniformity or unalterableness in a law of universal change. Through a slight confusion of thought and expression, this conviction may issue either in the sensational atomism of Locke or in the material atomism of popular science. A sensation is the unalterable effect of its conditions, whatever those conditions may be. It is unalterably related to other sensations. Our opinion about its conditions or relations may vary, but not the conditions or relations themselves, or the sensation determined by them. Hence when a man looks into his breast, as Locke bids him do, simple feelings—feelings apart from intellectual interpretations and combinations of them—seem alone unalterable in contrast with our judgments about them. In truth the unalterableness belongs not to any simple feeling, for our feelings change every moment upon us, but, as we have said, to the relation between it and its conditions or between it and other feelings; and such a relation is neither itself a feeling nor represented in our consciousness by a feeling. This distinction, however, is overlooked. The unalterableness of the fact that a certain feeling is felt under certain conditions, is ascribed to the simple feeling, or simple idea, as such: and unalterableness being the test by which we ascertain whether what we have believed to be the nature of any event is really so or not, the simple feeling, which by itself cannot properly be said to be really anything, comes to be regarded either as alone real, according to the ideal form of sensationalism, or as alone representing an external reality, according to the materialistic form of the same doctrine. (§ 25 ¶ 1)

On the other hand, reflection upon the perpetual flux of sensation suggests the view that it is not real in the same sense as its material conditions. The old dictum ascribed to Democritus—νόμῳ γλυκὺ καὶ νόμῳ πικρόν, νόμῳ θερμόν, νόμῳ ψυχρόν, νόμῳ χροίν· ἐτεῇ δὲ ἄτομα καὶ κενόν—expresses a way of thinking into which we often fall. The reality which in truth lies in the relations, according to the one law or system of relation, between feelings and their material conditions—not in the material conditions abstracted from the feelings any more than in the feelings abstracted from their material conditions—we are apt to ascribe exclusively to the latter. We think obscurely of matter and motion as real in some way in which nothing else is. Nor do we stop here. The demand for unalterableness in what we believe to be real, when once we are off the right track of seeking it in a uniform law of change, leads us to suppose that the reality of things is only reached when we have penetrated to atoms which in all changes of their motion and distribution remain intrinsically the same. (§ 25 ¶ 2)