The metaphysical discussion of identity is concerned with a •number of other questions such as the foregoing. It would lead us too far afield to discuss them all here.(See META PHYSICS). Philosophers discuss in this connec tion besides the various senses in which identity is known from qualitative likeness, in particular the relation of identity to difference; whether identity excludes difference, or on the contrary implies difference. Such questions are, on the whole, no doubt partly verbal, and partly psy chological; but they also lead very often back to very fundamental problems of philosophy.
(3) The psychological problem of personal identity was raised into prominence by the some what paradoxical discussion of Locke in his (Essay Concerning Human Understanding.' These discussions David Hume, in his (Treatise on Human Nature,' subsequently followed up with an analysis in keeping with ,the skeptical bias of his thought. The difficulties of the notion of personal identity which appear in these early essays are even more complicated in modern psychology. Into psychological literature of late have been introduced the terms "double personality," "double soul," and ego." To many minds the difficulties seem rather increased than diminished by the introduction of these strange combinations: they are phrases which tend rather to mystify than to clear our ideas. While the words serve for certain problems it is well to observe that authors are not lacking who deal with the psychological problem as if they were talking of a psychic fluid or vapor floating about us. On the bases of these hypotheses, of course everything becomes possible, and the human body may as easily be considered as not as the haunting place of two or even of a multi plicity of ghosts. We have no need of such hypotheses. For the spheres of the peripheral and the central soul are not distinctly separated by any definite boundary. Therefore the dif ficulties raised to meet the notion of personal identity by those who cite cases of double and alternating personality need not be regarded as insuperable.
A few observations on the situation as a whole will help us to grasp more easily the idea of a continuity underlying the notion of personal identity. First, a man is not the sum of the material particles of which at any given moment he consists. The material particles are not the really essential elements that makes a man what he is. For instance, all animals breathe the same air; but all animals are not therefore persons. In truth a man's material existence is constantly undergoing change, and yet we re main the same person to-day that we were yes terday. But let us ask a question; it will con firm our notion that this is true. Let one ask, am I for that reason another person because I cannot think the same thought twice with the same molecules? Does the thought change be cause the oxygen engaged in the first act of thinking has entered into new chemical com bination and is soon to be discarded from the system as waste? One knows that to answer this in the affirmative is like declaring that the significance of a word changes when it is writ ten once in pencil and once in ink. And yet it is not easy to discover the grounds of such conviction. For there are other considerations than materiality which appear to go yet deeper, making us seek the position of the continuity which we suspect to exist, even at a lower, more profound level. Says even Ernst Mach, whose achievements for psychology are by no means small: "It would hardly be possible for there to be greater difference in the egos of different men than appear in the course of a year in one man. When, to-day, I look back
upon my early youth, if the chain of recollec tion were not present to my mind, I should have to believe (apart from a few special points) that the boy was another individual." These and a number of equally interesting ob servations leads him to declare that the "ego is a little absolutely permanent as are bodies." We are prevented, however, from assenting to this conclusion by the consideration that our ego is in reality more than a current of sense impressions, as Mach understands it. Some un derstand by such words soul, ego, personality, etc., mere states of consciousness, and Mach here appears to be among them. It is apparent that a difference in terms is here the underlying difficulty. When Mach denies the independence and permanence of the ego, this is because he confuses the consciousness of the ego with the living ego itself. Our very knowledge is shaped by our independent work Moreover, it is necessary to call particular attention to the fact that above and beyond all intellectual proc esses there develops an inner life, a life which exhibits, in spite of all manifoldness, a per manent character, persisting through all changes and movements. Right through all his work and the complexities of his development man has always drawn further and further away from the mere life of his senses. He has more and more converted outward events into inner experience; more and more resisted th• mere influx of sensations. And all this is no mere intellectual phenomena. It is the unfolding of a rich actuality, the nearest and surest of which we have any knowledge; and this alone teaches us how mentally to shape and reshape our sense impressions. There is thus a unity of a spirit ual kind which persists with living force in the face of all the changes and obscurations of consciousness, as in sleep. As opposed to Mach's dissipation of the "ego,* there are thus experiences of the spiritual life which corrobo rate Goethe's conviction: "Und keine Zeit and keine Macht zerstCickelt Gepragte Form, die lebend sich entwickelt." Which may be freely translated "And neither Time nor Might dissolves Identity that life evolves." But let us examine yet a little more clearly. We have alluded to the familiar fact that ma terial of living beings are constantly changing. In anyone's body there persists no sameness of substance whatever. The identity of a living being is not maintained through the presence of a soul-monad, but through the pres ervation of its form. By life we understand organization. By soul we understand the form of an organism. Mind, spirit, soul, ego, are synonyms. We speak of soul when we em phasize the sentiments of a man; of mind when we refer mainly to man's rational powers; of spirit and ego when thinking of the significance and character of thought without reference to bodily conditions. That which pertains to soul is called psychical; that which has meaning is called spiritual: that which characterizes intel lection is called mental. All the many subcon scious and conscious memories which form the elements of our mentality are definite traces of former sense-impressions, reacting upon new sense impressions and embodying sentiments, and thoughts, the forms of which are preserved in the cerebral system, the substance of which is constantly changing. But man's personal identity consists not in any way in an identity of material particles, but in the sameness of soul-form which is preserved by the continuity of his existence. This we think is th whole secret of personal identity.