figuratively speaking, quite on one side. But even at the best, such a popular or empirical psychology has no special claim to be ranked as science. It may no doubt be said that at least it collects, describes, or notes down facts. But even this is not so certain as it seems. Its so-called facts are very largely fictions, or so largely interpolated with error, that they cannot be safely used for construction. If psychology is to accomplish anything valuable, it must go more radically to work. It must—at least in a measure—discard from its preliminary view the data of common and current distinctions, and try to get at something more primary or ultimate as its starting-point. And this it may do in two ways. It may, in the one case, follow the example of the physical sciences. In these it is the universal practice to assume that the explanation of complex and concrete facts is to be attained by (_a_) postulating certain simple elements (which we may call atoms, molecules, and perhaps units or monads), which are supposed to be clearly conceivable and to justify themselves by intrinsic intelligibility, and by (_b_) assuming that these elements are compounded and combined according to laws which again are in the last resort self-evident, or such that they seem to have an obvious and palpable lucidity. Further, such laws being always axioms or plain postulates of mechanics (for these alone possess this feature of self-evident intelligibility), they are subject to and invite all the aids and refinements of the higher mathematical calculus. What the primary and self-explicative bits of psychical reality may be, is a further question on which there may be some dispute. They may be, so to say, taken in a more physical or in a more metaphysical way: i.e. more as units of nerve-function or more as elements of ideative-function. And there may be differences as to how far and in what provinces the mathematical calculus may be applicable. But, in any case, there will be a strong tendency in psychology, worked on this plan, to follow, _mutatis mutandis_, and at some distance perhaps, the analogy of material physics. In both the justification of the postulated units and laws will be their ability to describe and systematise the observed phenomena in a uniform and consistent way.