The whole subject of mental differentiation needs clarifying. Are we to consider mind merely as a sum of many distinct modes each of which has, in the course of evolution, appeared suddenly in answer to the demands of life at a critical period, and is faint, indeed, yet from the first having a distinct and peculiar quality by which it suitably stimulates will, and that the sole growth of these diverse forms has been in intensity and by various associations with other states? or are we to consider that mind was originally a very general vague state, which, by a continuous and traceable differentiation, has slowly developed into many different modes? Certainly the latter seems the more rational. To conceive that there are no essential and radical subdivisions in mind, that not even knowing, feeling, and willing, are fundamentally primitive, but each, and each form of each, but modifications of precedent modes, this is a theory which is enticing in its simplicity and in its analogy to physical evolution from a single underlying material element. But when we come to particular investigations, as this of the origin and development of hate, we cannot well discover any modes intermediate between it and say, anger, which are the links in a continuous evolution, but for aught we can see or conceive, hate is as much hate the first time it appears as at any subsequent time. The links in the evolution of mind from phase to phase are all missing, and how are we to supply them? Of necessity as subjective facts they must first be realized, before they can be known, but how can this be done by a consciousness which has long outgrown them? We cannot discover these fossil and extinct forms objectively, as the paleontologist discovers extinct species, but in some way we must re-enact and re-experience them in our own consciousness before we can know anything about them. If every mind embryologically passes through the several stages of its general evolution in the race, still the strange intermediate forms which might then have existed are beyond the recall of the reflective stage, when we first demand to know the history of mind. And when we appeal to comparative psychology we are equally in the dark, for we must judge animals by ourselves, we can interpret their consciousness only by our own, and they may have very rude and peculiar forms which are unknown and unknowable by us. Thus the limitations and difficulties of subjective research are especially brought up to us in evolutionary study which thus seems wholly confined to _a priori_ speculation. While we can conceive it likely that hate was suddenly brought into full being by the demands of life, yet it is hardly a rational view of emotion to regard it as a _per saltum_ series of distinct psychical species called successively into being by the exigencies of existence, which indeed, is a view almost as ultra-scientific as that which regards all mental modes as direct endowments from Deity.