Various objections brought forward by philosophers immediately after this book was first published induce me to add the following brief statement to this revised edition. I can well understand that there are readers for whom the rest of the book is of interest, but who will regard the following as superfluous, as a remote and abstract spinning of thoughts. They may well leave this short description unread. However, problems arise within philosophical world views which originate in certain prejudices on the part of the philosophers, rather than in the natural sequence of human thinking in general. What has so far been dealt with here appears to me to be a task that confronts every human being who is striving for clarity about man's being and his relationship to the world. What follows, however, is rather a problem which certain philosophers demand should be considered when such questions are under discussion as those dealt with here, because through their whole way of thinking, they have created difficulties which do not otherwise exist. If one simply ignores such problems, certain people will soon come forward with accusations of dilettantism and so on. And the opinion arises that the author of a discussion such as this book contains has not thought out his position in regard to those views he does not mention in the book.
The problem to which I refer is this: There are thinkers who are of the opinion that a particular difficulty exists when it is a question of understanding how the soul life of another person can affect one's own (the soul life of the observer). They say: My conscious world is enclosed within me; the conscious world of another person likewise is enclosed within him. I cannot see into the world of another's consciousness. How, then, do I come to know that we share the same world? A world view which considers that from a conscious sphere it is possible to draw conclusions about an unconscious sphere that can never become conscious, attempts to solve this difficulty in the following way. This world view says: The content of my consciousness is only a representative of a real world which I cannot consciously reach. In that real world lies the unknown cause of the content of my consciousness. In that world is also my real being, of which likewise I have in my consciousness only a representative. And in it exists also the being of the other person who confronts me. What is experienced consciously by him has its corresponding reality in his real being, independent of his consciousness. This reality reacts on my fundamental but unconscious being in the sphere that cannot become conscious, and in this way a representative that is quite independent of my conscious experience is produced in my consciousness. One sees here that to the sphere accessible to my consciousness, hypothetically is added another sphere, inaccessible to my consciousness, and this is done because it is believed that we would otherwise be forced to maintain that the whole external world which seems to confront me is only a world of my consciousness, and this would result in the — solipsistic — absurdity that the other persons also exist only in my consciousness.
It is possible to attain clarity about this problem, which has been created by several of the more recent approaches to a theory of knowledge, if one endeavors to survey the matter from the point of view that observes facts in accordance with their spiritual aspect, as presented in this book. To begin with, what do I have before me when I confront another personality? Let us consider what the very first impression is. The first impression is the physical, bodily appearance of the other person, given me as perception, then the audible perception of what he is saying, and so on. I do not merely stare at all this; it sets my thinking activity in motion. To the extent that I confront the other personality with my thinking, the perceptions become transparent to my soul. To the extent that I grasp the perceptions in thinking, I am obliged to say that they are not at all what they appear to be to the external senses. Within the perceptions as they appear directly to the senses something else is revealed, namely what they are indirectly. The fact that I bring them before me means at the same time their extinction as mere appearances to the senses. But what, in their extinction, they bring to revelation, this, for the duration of its effect on me, forces me — as a thinking being — to extinguish my own thinking and to put in its place the thinking of what is revealed. And this thinking I grasp as an experience that is like the experience of my own thinking. I have really perceived the thinking of the other. For the direct perceptions, which extinguish themselves as appearances to the senses, are grasped by my thinking, and this is a process that takes place completely within my consciousness; it consists in the fact that the thinking of the other takes the place of my thinking. The division between the two spheres of consciousness is actually canceled out through the extinction of the appearances to the senses. In my consciousness this expresses itself in the fact that in experiencing the content of the other's consciousness I am aware of my own consciousness as little as I am aware of it in dreamless sleep. Just as my day-consciousness is excluded in dreamless sleep, so in the perceiving of the foreign content of consciousness, the content of my own is excluded. There are two reasons why one tends to be deluded about these facts; one is that in perceiving the other person, the extinction of the content of one's own consciousness is replaced not by unconsciousness as in sleep, but by the content of the other's consciousness; the other reason is that the alternation between extinction and re-appearance of self-consciousness occurs too quickly to be noticed in ordinary life. — This whole problem cannot be solved by an artificial construction of concepts which draws conclusions from what is conscious to what can never become conscious, but by actual experience of what occurs in the union of thinking with perception. Instances like the above often occur in regard to many problems which appear in philosophical literature. Thinkers should seek the path to unprejudiced observation in accordance with facts, both physical and spiritual, but instead they erect an artificial construction of concepts, inserting this between themselves and reality.
Eduard von Hartmann, in an essay  includes my Philosophy of Spiritual Activity among philosophical works which are based on “epistemological monism.” And this theory is rejected by him as one that cannot even be considered. The reason for this is as follows. According to the viewpoint expressed in the essay mentioned above, only three possible epistemological standpoints exist. The first is when a person remains at the naive standpoint and takes perceived phenomena to be realities existing outside of human consciousness. In this case critical insight is lacking. It is not recognized that after all one remains with the content of one's consciousness merely within one's own consciousness. It is not realized that one is not dealing with a table-in-itself but only with the object of one's own consciousness. One remaining at this standpoint, or returning to it for any reason, is a naive realist. However, this standpoint is impossible, for it overlooks the fact that consciousness has no other object than itself. The second standpoint is when all this is recognized and is taken into account fully. Then to begin with, one becomes a transcendental idealist. As transcendental idealist one has to give up hope that anything from a “thing-in-itself” could ever reach human consciousness. And if one is consistent, then it is impossible not to become an absolute illusionist. For the world one confronts is transformed into a mere sum of objects of consciousness, and indeed only objects of one's own consciousness. One is forced to think of other people too — absurd though it is — as being present only as the content of one's own consciousness. According to von Hartmann the only possible standpoint is the third one, transcendental realism. This view assumes that “things-in-themselves” exist, but our consciousness cannot have direct experience of them in any way. Beyond human consciousness — in a way that remains unconscious — they are said to cause objects of consciousness to appear in human consciousness. All we can do is to draw conclusions about these “things-in-themselves” from the merely represented content of our consciousness which we experience. In the essay mentioned above, Eduard von Hartmann maintains that “epistemological monism” — and this he considers my standpoint to be — would in reality have to confess to one of the three standpoints just mentioned; this is not done, because the epistemological monist does not draw the actual conclusion of his presuppositions. The essay goes on to say:
“If one wants to find out what position a supposed monist occupies in regard to a theory of knowledge, it is only necessary to ask him certain questions and compel him to answer them. Voluntarily he will not give any opinion on these points, and he will go to any length to avoid answering direct questions on them, because each answer will show that as a monist his claim to belong to some other standpoint than one of the above three, in relation to a theory of knowledge, is out of the question. These questions are as follows: 1) Are things continuous or intermittent in their existence? If the answer is: They are continuous, then we are dealing with one form or another of naive realism. If the answer is: They are intermittent, then we have transcendental idealism. But if the answer is: They are on the one hand continuous (as content of the absolute consciousness, or as unconscious representations, or existing as possibilities of perceptions), on the other hand they are intermittent (as content of limited consciousness), then we recognize transcendental realism. — 2) If three persons sit at a table, how many examples of the table are present? He who answers: One, is a naive realist; he who answers: Three, is a transcendental idealist; but he who answers: Four, is a transcendental realist. This last answer does indeed presuppose that it is legitimate to put under the one heading, 'examples of the table' something so dissimilar as the one table as thing-in-itself, and the three tables as perceptual objects in the three consciousnesses. Whoever finds this too much will have to answer 'one and three' instead of 'four.' — 3) If two persons are in a room by themselves, how many examples of these persons are present? One answering: Two, is a naive realist; one answering: Four (namely, one 'I' and one 'other' in each of the two consciousnesses), is a transcendental idealist; but one answering: Six (namely, two persons as 'things-in-themselves' and four objects of representation of persons in the two consciousnesses), is a transcendental realist. One wishing to prove that epistemological monism is a different standpoint from any of these three, would have to answer each of the above questions differently, and I cannot imagine what such answers could be.”
The answers of The Philosophy of Spiritual Activity would be: 1) He who only grasps the perceptual content and takes this to be the reality, is a naive realist; he does not make it clear to himself that he can actually regard the perceptual content as enduring only so long as he is looking at it and he must, therefore, think of what he has before him as intermittent. However, as soon as he realizes that reality is present only when the perceptual content is permeated by thought, he reaches the insight that the perceptual content that comes to meet him as intermittent, is revealed as continuous when it is permeated with what thinking elaborates. Therefore: the perceptual content, grasped by a thinking that is also experienced, is continuous, whereas what is only perceived must be thought of as intermittent — that is, if it were real, which is not the case. — 2) When three persons are sitting at a table, how many examples of the table are present? One table only is present; but as long as the three persons remain at their perceptual pictures they will have to say: These perceptual pictures are no reality at all. And as soon as they pass over to the table as grasped in their thinking, there is revealed to them the one reality of the table; with their three contents of consciousness they are united in this one reality. — 3) When two persons are in a room by themselves, how many examples of these persons are present? There are most definitely not six examples present — not even in the sense of transcendental realism — there are two. Only to begin with, each of the two persons has merely the unreal perceptual, picture of himself as well as that of the other person. Of these pictures there are four, and the result of their presence in the thinking-activity of the two persons is that reality is grasped. In their thinking-activity each of the persons goes beyond the sphere of his own consciousness; within each of them lives the sphere of the other person's consciousness, as well as his own. At moments when this merging takes place, the persons are as little confined within their own consciousness as they are in sleep. But the next moment, consciousness of the merging with the other person returns, so that the consciousness of each person — in his experience of thinking — grasps himself and the other. I know that the transcendental realist describes this as a relapse into naive realism. But then I have already pointed out in this book that naive realism retains its justification when applied to a thinking that is experienced. The transcendental realist does not enter into the actual facts concerned in the process of knowledge; he excludes himself from them by the network of thoughts in which he gets entangled. Also, the monism which is presented in the Philosophy of Spiritual Activity should not be called “epistemological,” but rather, if a name is wanted, a monism of thought. All this has been misunderstood by Eduard von Hartmann. He did not enter into the specific points raised in the Philosophy of Spiritual Activity, but maintained that I had made an attempt to combine Hegel's universalistic panlogism  with Hume's  individualistic phenomenalism  whereas in actual fact the Philosophy of Spiritual Activity has no similarity with these two views it is supposed to combine. (This is also the reason I did not feel inclined to compare my view with the “epistemological monism” of Johannes Rehmke,  for example. In fact, the viewpoint of the Philosophy of Spiritual Activity is utterly different from what Eduard von Hartmann and others call epistemological monism.)