§ 379. Even our own sense of the mind’s _living_ unity naturally protests against any attempt to break it up into different faculties, forces, or, what comes to the same thing, activities, conceived as independent of each other. But the craving for a _comprehension_ of the unity is still further stimulated, as we soon come across distinctions between mental freedom and mental determinism, antitheses between free _psychic_ agency and the corporeity that lies external to it, whilst we equally note the intimate interdependence of the one upon the other. In modern times especially the phenomena of _animal magnetism_ have given, even in experience, a lively and visible confirmation of the underlying unity of soul, and of the power of its “ideality.” Before these facts, the rigid distinctions of practical common sense were struck with confusion; and the necessity of a “speculative” examination with a view to the removal of difficulties was more directly forced upon the student. § 380. The “concrete” nature of mind involves for the observer the peculiar difficulty that the several grades and special types which develop its intelligible unity in detail are not left standing as so many separate existences confronting its more advanced aspects. It is otherwise in external nature. There, matter and movement, for example, have a manifestation all their own—it is the solar system; and similarly the _differentiae_ of sense-perception have a sort of earlier existence in the properties of _bodies_, and still more independently in the four elements. The species and grades of mental evolution, on the contrary, lose their separate existence and become factors, states and features in the higher grades of development. As a consequence of this, a lower and more abstract aspect of mind betrays the presence in it, even to experience, of a higher grade. Under the guise of sensation, e.g., we may find the very highest mental life as its modification or its embodiment. And so sensation, which is but a mere form and vehicle, may to the superficial glance seem to be the proper seat and, as it were, the source of those moral and religious principles with which it is charged; and the moral and religious principles thus modified may seem to call for treatment as species of sensation. But at the same time, when lower grades of mental life are under examination, it becomes necessary, if we desire to point to actual cases of them in experience, to direct attention to more advanced grades for which they are mere forms. In this way subjects will be treated of by anticipation which properly belong to later stages of development (e.g. in dealing with natural awaking from sleep we speak by anticipation of consciousness, or in dealing with mental derangement we must speak of intellect). What Mind (or Spirit) is.