generalization of certain sequences? Does not the explanation of the naturalist contain an entirely different element? He does not merely want to say that this effect has sometimes been observed and that there is thus probability that it will come again, when similar causes are given. No, the physicist wants to understand those connections of cause and effect as necessary ones. He tries to find sequences which cannot be otherwise because they cannot be thought in any other way. Therefore he is not satisfied with complex regularities, but analyzes them until he can bring them down to simple physical connections, and these physical connections finally to mechanical processes, which realize for us logical necessities. That matter lasts and cannot disappear is such a presupposition, which comes to us with the necessity of logical thinking. We simply cannot think it otherwise. And the whole idea of natural science is to conceive the physical universe in such a way that all changes in the outer world can be understood as the movements of its parts in accordance with such necessary physical axioms. If we knew all the atoms of the present status of the universe, and we knew every present movement of every atom, we should be able to foresee the position of every atom in the next moment and in the following moment and in all following moments, and all that by the necessary continuation of the substance and its energies. That alone is the background of all special physical inquiry, and we rely on the special laws of physics and chemistry, because we trust that this universe, as a whole, could be ultimately understood as such a system of necessary changes in the positions of the lasting atoms.

For the psychologist there is no hope of finding such necessity in the mental processes. The point is not that psychology is to-day too far removed from the fulfillment of such an ideal, the point is rather that such an ideal would be meaningless for the psychologist. His materials, the psychical contents of consciousness, are by their nature unfit to enter into such necessary connections; they cannot do it because they cannot last. The physical object, we saw, is the object which is common property, which we all feel in common, which must thus exist for all time. The things in nature may burn down or decay, but no atom of them can ever disappear from the universe, each must enter into new and ever new combinations and last through all changes. The psychical thing, on the other hand, can exist only for the one immediate experience. Every sensation which enters into my ideas or volitions or emotions is a new creation of the instant which cannot last; each one flashes up and is lost with the moment's experience. My will to-day may have the same aim as my will of yesterday, but as psychical object, my will to-day is a new will, is a new creation in every pulse beat of my life. I must will it again, I cannot store it up. And my joy of to-day can never be as psychical fact the same joy which I may have to-morrow. Mental objects as such, as psychological material, are not destined to last. It has no meaning whatever to think of their being kept over until another time. It is a coarse materialism to conceive the mental contents like pebbles which may remain on the road from one day to another. Our ideas and feelings are mental appearances which have their existence in the act of the one experience; each new experience must be an entirely new creation.

If I remember my last year's perception, I do not dig it out from an under-mind, in which it was stored up and buried, but I create an entirely new memory picture, just as I may make to-day a speech which says the same thing which I said last year, and yet my action of speaking is not last year's speech movement. It is a new action, and the movement did not lie over somewhere during the interval. Mental life is produced anew in every moment. When the first experience is gone and the second comes, nothing of the stuff from which the first was made still has existence in the content of consciousness. By this fact it becomes entirely impossible ever to conceive necessary connections in the sense of physical necessity in the world of consciousness. The one idea may bring to me another idea by association, but as long as I consider both strictly as mental facts, I can never understand why this association happens, I can never grasp the real mechanism of the connection, I can never see necessity between the disappearance of the one and the appearance of the other. It remains a mystery which does not justify any expectation that the same sequence will result again. Whatever belongs to the psychical world can never be linked by a real insight into necessity. Causality there remains an empty name without promise of a real explanation.

Only when we have recognized this fundamental difficulty in the efforts for psychological explanation, can we understand the way which modern psychology has taken most successfully. The end of this way is simply this: every psychical fact is to be thought of as an accompaniment of a physical process and the necessary connections of these physical processes determine, then, the connections of the mental facts. Indeed this has become the method of modern psychology. It has brought about the intimate relation between psychology and the physiology of the brain, and has given us, as foundation, the theory of psychophysical parallelism; the theory that there is no psychical process without a parallel brain process. But the real center of the theory lies indeed in the fact which we discussed; it lies in the fact that we cannot have any explanation of mental states as such at all, if we do not link them with physical processes.

Is it necessary to express again the assurance that such statements of a parallelism between mind and brain in no way interfere with an idealistic view of inner life? Have we not seen clearly enough that these mental facts which are conceived parallel to physiological brain processes do not represent the immediate reality of our inner life, that our life reality is purposive and as such outside of all causal explanation, and that we have to take a special, almost artificial, point of view to consider inner life at all as objects, as contents of consciousness, and thus as psychological material? But since we have seen that for certain purposes such a point of view is necessary, as soon as we have taken it we must be consistent. Our inner life in its purposive reality has therefore nothing to do with brain processes, but if we are on the psychological track and consider man as a system of psychological phenomena, then to be sure, we must see that our only possible interest lies in the finding of necessary causal connections. But these cannot be found otherwise than by linking the mental facts with the physical ones, the psychological material with the processes of the brain.

Of course, that mental experience stands in intimate relations to the body is a knowledge which does not wait for such philosophical arguments. That mind and body come in contact is a conviction which goes with every single sense perception. I see and hear because light and sound stimulate my sense organs, and the sense organs stimulate my brain. The explanation of perception through causes in the physical system seems the more natural as it is evident that in such cases there are no psychical causes which might have brought forward the perception. If I suddenly hear bells ringing, there was on the mental side nothing preceding which could be responsible for my sound perception. And the same holds true if the physical source lies in my own body, if perhaps my tooth begins to ache, although no expectation preceded it.

In the same way it seems a matter of course that mind