The system of knowledge is thus the system of experience with all that is involved in it in so far as it demands submission from our over-individual will, and the classification which we are seeking must be thus a division and subdivision of our over-individual submissions. But the submission itself can be of very different characters and these various types must give the deepest logical principles of scientific classification. To point at once to the fundamental differences: our will acknowledges the demands of other wills and of objects. We cannot live our life—and this is not meant in a biological sense, but, first of all, in a teleological sense—our life becomes meaningless, if our will does not respect the reality of will-demands and of objects of will. Now we have seen that the will which demands our decision may be either the individual will of other subjects or the over-individual will, which belongs to every subject as such and is independent of any individuality. We can say at once that in the same way we are led to acknowledge that the object has partly an over-individual character, that is, necessarily belongs to the world of objects of every possible subject, and partly an individual character, as our personal object. We have thus four large groups of experiences to which we submit ourselves: over-individual will-acts, individual will-acts, over-individual objects, individual objects. They constitute the first four large divisions of our system.

The over-individual will-acts, which are as such teleologically binding for every subject and therefore norms for his will, give us the Normative Sciences. The individual will-acts in the world of historical manifoldness give us the Historical Sciences. The objects, in so far as they belong to every individual, make up the physical world, and thus give us the Physical Sciences; and finally the objects, in so far as they belong to the individual, are the contents of consciousness, and thus give us the Mental Sciences. We have then the demarcation lines of our first four large divisions: the Normative, the Historical, the Physical, and the Mental Sciences. Yet their meaning and method and difference must be characterized more fully. We must understand why we have here to deal with four absolutely different types of scientific systems, why the over-individual objects lead us to general laws and to the determination of the future, while the study of the individual will-acts, for instance, gives us the system of history, which turns merely to the past and does not seek natural laws; and why the study of the norms gives us another kind of system in which neither a causal nor an historical, but a purely logical connection prevails. Yet all these methodological differences result necessarily from the material with which these four different groups of sciences are working.

Let us start again from the consideration of our original logical purpose. We feel ourselves bound and limited in our will by physical things, by psychical contents, by the demands of other subjects, and by norms. The purpose of all our knowledge is to develop completely all that is involved in this bondage. We want to develop in an over-individual way all the obligations for our submission which are necessarily included in the given objects and the given demands of subjects. We start of course everywhere and in every direction from the actual experience, but we expand the experience by seeking those objects and those demands to which, as necessarily following from the immediately given experience, we must also submit. And in thus developing the whole system of submissions, the interpretation of the experience itself becomes transformed: the physicist may perhaps substitute imperceptible atoms for the physical object and the psychologist may substitute sensations for the real idea, and the historian may substitute combinations of influences for the real personality, and the student of norms may substitute combinations of conflicting demands for the one complete duty; yet in every case the substitution is logically necessary and furnishes us what we call truth inasmuch as it is needed to develop the concrete system of our submissions and thus to express our confidence in the order-lines of reality. And each of these substitutions and supplementations becomes, as material of knowledge, itself a part of the world of experience.

3. The Physical and the Mental Sciences

The physicist, we said, speaks of the world of objects in so far as they belong to every possible subject, and are material for a merely passive spectator. Of course the pure experience does not offer us anything of that kind. We insisted that the objects of our real life are objects of our will and of our attitudes, and are at the same time undifferentiated into the physical things outside of us and the psychical ideas in us. To reach the abstraction of the physicist, we have thus to cut loose the objects from our will and to separate the over-individual elements from the individual elements. Both transformations are clearly demanded by our logical aims. As to the cutting loose from our will, it means considering the object as if it existed for itself, as if it were a mere passively given material and not a material of our personal interests. But just that is needed. We want to find out how far we have to submit ourselves to the object. If we want to live our life, we must adjust our attitudes to things, and, as we know our will, we must seek to understand the other factor in the complex experience, the object of our will, and we must find out what it involves in itself. But we do not understand the object and the submission which it demands if we do not completely understand its relation to our desires. Our total submission to the thing thus involves our acknowledgment of all that we have to expect from it. And although the real experience is a unity of will and thing, we have thus the most immediate interest in considering what we have to expect from the thing in itself, without reference to our will. That means finding out the effects of the given object with a subject as the passive spectator. We eliminate artificially, therefore, the activity of the subject and construct as presupposition for this circle of knowledge a nowhere existing subject without activity, for which the thing exists merely as a cause of the effects which it produces.

The first step towards natural science is, therefore, to dissolve the real experience into thing and personality; that is, into object and active subject, and to eliminate in an artificial abstraction the activity of the subject, making the object material of merely passive awareness, and related no longer to the will but merely to other objects. It may be more difficult to understand the second step which naturalism has to take before a natural science is possible. It must dissolve the object of will into an over-individual and an individual part and must eliminate the individual. That part of my objects which belongs to me alone is their psychical side; that which belongs to all of us and is the object of ever new experience is the physical object. As a physicist, in the widest sense of the word, I have to ignore the objects in so far as they are my ideas and have to consider the stones and the stars, the inorganic and the organic objects, as they are outside of me, material for every one. The logical purpose of this second abstraction may be perhaps formulated in the following way.

We have seen that the purpose of the study of the objects is to find out what we have to expect from them; that is, to what effects of the given thing we have to submit ourselves in anticipation. The ideal aim is thus to understand completely how present objects and future objects—that is, how causes and effects—are connected. The first stage in such knowledge of causal connections is, of course, the observation of empirical consequences. Our feeling of expectation grows with the regularity of observed succession; yet the ideal aim can never be fulfilled in that way. The mere observation of regularities can help us to reduce a particular case to a frequently observed type, but what we seek to understand is the necessity of the process. Of course we have to formulate laws, and as soon as we acknowledge a special law to be expressive of a necessity, the subsumption of the particular case under the law will satisfy us even if the necessity of the connection is not recognized in the particular case. We are satisfied because the acknowledgment of the law involved all possible cases. But we do not at all feel that we have furnished a real explanation if the law means to us merely a generalization of routine experiences, and if thus no absolute validity is attached to the law. This necessity between cause and effect must thus have its ultimate reason in our own understanding. We must be logically obliged to connect the objects in such a way, and wherever observation seems to contradict that which is logically necessary, we must reshape our idea of the object till the demands of reason are fulfilled. That is, we must substitute for the given object an abstraction which serves the purpose of a logically necessary connection. That demand is clearly not satisfied if we simply group the totality of such causal judgments under the single name, Causality, and designate thus all these judgments as results of a special disposition of the understanding. We never understand why just this cause demands just this effect so long as we rely on such vague and mystical power of our reason to link the world by causality.

But the situation changes at once if we go still further back in the categories of our understanding. While a mere demand for causality never explains what cause is to be linked with what effect, the vagueness disappears when we understand this demand for causality itself as the product of a more fundamental demand for identity. That an object remains identical with itself does not need for us any further interpretation. That is the ultimate presupposition of our thought, and where a complete identity is found nothing demands further explanation. All scientific effort aims at so rethinking different experiences that they can be regarded as partially identical, and every discovery of necessary connection is ultimately a demonstration of identity. If we seek connections with the final aim to understand them as necessary, we must conceive the world of our objects in such a way that it is possible to consider the successive experiences as parts of a self-identical world; that is, as parts of a world in which no substance and no energy can disappear or appear anew. To reach this end it is obviously needed that we eliminate from the world of objects all that cannot be conceived as identically returning in a new experience; that is, all that belongs to the present experience only. We do eliminate this by taking it up conceptually into the subject and calling it psychical, and thus leaving to the object merely that which is conceived as belonging to the world of everybody's experience, that is, of over-individual experience. The whole history of natural science is first of all the gigantic development of this transformation, resolution, and reconstruction. The objects of experience are re-thought till everything is eliminated which cannot be conceived as identical with itself in the experiences of all individuals and thus as belonging to the over-individual world. All the substitutions of atoms for the real thing, and of energies for the real changes, are merely conceptional schemes to satisfy this demand.

The logically primary step is thus not the separation of the physical and the psychical things plus the secondary demand to connect the physical things causally; the order is exactly opposite. The primary desire is to connect the real objects and to understand them as causes and effects. This understanding demands not only empirical observation, but insight into the necessary connection. Necessary connection, on the other hand, exists merely for identical objects and identical qualities. But in the various experiences only that is identical which is independent of the momentary individual experiences, and therefore we need as the ultimate aim a reconstruction of the object into the two parts, the one perceptional, which refers to our individual experience; and the other conceptional, which expresses that which can be conceived as identical in every new experience. The ideal of this constructed world is the mechanical universe in which every atom moves by causal necessity because there is nothing in that universe, no element of substance and no element of energy, which will not remain identical in all changes of the universe which are possibly to be expected. It becomes completely determinable by anticipation and the system of our submissions to the object can be completely constructed. The totality of intellectual efforts to reconstruct such a causally connected over-individual world of objects clearly represents a unity of its own. It is the system of physical sciences.

The physical universe is thus not the totality of our objects. It is a substitution for our real objects, constructed by eliminating the individual parts of our objects of experience. These individual parts are the psychical aspects of our objective experience, and they clearly awake our scientific interest too. The physical sciences need thus as counterpart a division of mental sciences. Their aim must be the same. We want to foresee the psychical results and to understand causally the psychical experience. Yet it is clear that the plan of the mental sciences must be quite different in principle from that of the sciences of nature. The causal connection of the physical universe was ultimately anchored in the identity of the object through various experiences; while the object of experience was psychical for us just in so far as it could never be conceived as identical in different phases of reality. The psychical object is an ever new creation; my idea can never be your idea. Their meaning may be identical, but the psychical stuff, the content of my consciousness, can never be object for any one else, and even in myself the idea of to-day is never the idea of yesterday or to-morrow. But if there cannot be identity in different psychical experiences, it is logically impossible to connect them directly by necessity. If we yet want to master their successive appearance, we must substitute an indirect connection for the direct one, and must describe and explain the psychical phenomena through reference to the physical world. It is in this way that modern psychology has substituted elementary sensations for the real contents of consciousness and has constructed relations between these elementary mental states on the basis of processes in the organism, especially brain processes. Here, again, reality is left behind and a mere conceptional construction is put in its place. But this construction fulfills its purpose and thus gives us truth; and if the basis is once given, the psychological sciences can build up a causal system of the conscious processes in the individual man and in society.