First of all, however, the following very essential remark. I hope that in the preceding book I have succeeded in producing the conviction that what in the Kantian philosophy is called the thing-in-itself, and appears therein as so significant but obscure and paradoxical a doctrine, is, if reached by the entirely different path we have taken, nothing but the will in the sphere of this concept, widened and defined in the way I have stated. It appears obscure and paradoxical in Kant especially through the way in which he introduced it, namely by inference from what is grounded to what is the ground, and it was considered to be a stumbling-block, in fact the weak side of his philosophy. Further, I hope that, after what has been said, there will be no hesitation in recognizing again in the definite grades of the objectification of that will, which forms the in-itself of the world, what Plato called the eternal Ideas or unchangeable forms (εἴδη). Acknowledged to be the principal, but at the same time the most obscure and paradoxical, dogma of his teaching, these Ideas have been a subject of reflection and controversy, of ridicule and reverence, for many and very differently endowed minds in the course of centuries.
Now if for us the will is the thing-in-itself, and the Idea is the immediate objectivity of that will at a definite grade, then we find Kant’s thing-in-itself and Plato’s Idea, for him the only ὄντως ὄν80—those two great and obscure paradoxes of the two greatest philosophers of the West—to be, not exactly identical, but yet very closely related, and distinguished by only a single modification. The two great paradoxes, just because, in spite of all inner harmony and relationship, they sound so very different by reason of the extraordinarily different individualities of their authors, are even the best commentary on each other, for they are like two entirely different paths leading to one goal. This can be made clear in a few words. What Kant says is in essence as follows: “Time, space, and causality are not determinations of the thing-in-itself, but belong only to its phenomenon, since they are nothing but forms of our knowledge. Now as all plurality and all arising and passing away are possible only through time, space, and causality, it follows that they too adhere only to the phenomenon, and by no means to the thing-in-itself. But since our knowledge is conditioned by these forms, the whole of experience is only knowledge of the phenomenon, not of the thing-in-itself; hence also its laws cannot be made valid for the thing-in-itself. What has been said extends even to our own ego, and we know that only as phenomenon, not according to what it may be in itself.” This is the meaning and content of Kant’s teaching in the important respect we have considered. Now Plato says: ”The things of this world, perceived by our senses, have no true being at all; they are always becoming, but they never are. They have only a relative being; they are together only in and through their relation to one another; hence their whole existence can just as well be called a non-being. Consequently, they are likewise not objects of a real knowledge (ἐπιστήμη), for there can be such a knowledge only of what exists in and for itself, and always in the same way. On the contrary, they are only the object of an opinion or way of thinking, brought about by sensation (δóξα μετ’ αἰσθήσεως ἀλóγoυ).81 As long as we are confined to their perception, we are like persons sitting in a dark cave, and bound so fast that they cannot even turn their heads. They see nothing but the shadowy outlines of actual things that are led between them and a fire which burns behind them; and by the light of this fire these shadows appear on the wall in front of them. Even of themselves and of one another they see only the shadows on this wall. Their wisdom would consist in predicting the sequence of those shadows learned from experience. On the other hand, only the real archetypes of those shadowy outlines, the eternal Ideas, the original forms of all things, can be described as truly existing (ὄντως ὄν), since they always are but never become and never pass away. No plurality belongs to them; for each by its nature is only one, since it is the archetype itself, of which all the particular, transitory things of the same kind and name are copies or shadows. Also no coming into existence and no passing away belong to them, for they are truly being or existing, but are never becoming or vanishing like their fleeting copies. (But in these two negative definitions there is necessarily contained the presupposition that time, space, and causality have no significance or validity for these Ideas, and do not exist in them.) Thus only of them can there be a knowledge in the proper sense, for the object of such a knowledge can be only that which always and in every respect (and hence in-itself) is, not that which is and then again is not, according as we look at it.” This is Plato’s teaching. It is obvious, and needs no further demonstration, that the inner meaning of both doctrines is wholly the same; that both declare the visible world to be a phenomenon which in itself is void and empty, and which has meaning and borrowed reality only through the thing that expresses itself in it (the thing-in-itself in the one case, the Idea in the other). To this latter, however, which truly is, all the forms of that phenomenon, even the most universal and essential, are, in the light of both doctrines, entirely foreign. In order to deny these forms, Kant has directly expressed them even in abstract terms, and has definitely deprived the thing-in-itself of time, space, and causality, as being mere forms of the phenomenon. On the other hand, Plato did not reach the highest expression, and only indirectly did he deprive his Ideas of those forms, in that he denied of the Ideas what is possible only through those forms, namely plurality of the homogeneous, origination and disappearance. Though it is superfluous, I wish to make this remarkable and important agreement clear by an example. Let us suppose an animal standing before us in the full activity of its life. Plato will say: “This animal has no true existence, but only an apparent one, a constant becoming, a relative existence that can just as well be called non-being as being. Only the Idea which is depicted in that animal is truly ‘being’ or the animal-in-itself (αὐτὸ τὸ θηρíoν), which is dependent on nothing, but which is in and by itself (ϰαθ’ ἑαυτó, ἀεὶ ὡσαύτως) ;82 it has not become, it is not passing away, but always is in the same way (ἀεὶ ὄν, ϰαὶ μηδέπoτε oὔτε γιγνóμενoν, oὔτε ἀπoλλύμενoν).83 Now, in so far as we recognize in this animal its Idea, it is all one and of no importance whether we now have before us this animal or its progenitor of a thousand years ago; also whether it is here or in a distant country; whether it presents itself in this manner, posture, or action, or in that; finally, whether it is this or any other individual of its species. All this is void and unreal, and concerns only the phenomenon; the Idea of the animal alone has true being, and is the object of real knowledge.” Thus Plato. Kant would say something like this: “This animal is a phenomenon in time, space, and causality, which are collectively the conditions a priori of the possibility of experience residing in our faculty of knowledge, not determinations of the thing-in-itself. Therefore this animal, as we perceive it at this particular time, in this given place, as an individual that has come into existence and will just as necessarily pass away in the connexion of experience, in other words, in the chain of causes and effects, is not a thing-in-itself, but a phenomenon, valid only in reference to our knowledge. In order to know it according to what it may be in itself, and so independently of all determinations residing in time, space, and causality, a different kind of knowledge from that which is alone possible to us through the senses and understanding would be required.”
In order to bring Kant’s expression even closer to Plato’s, we might also say that time, space, and causality are that arrangement of our intellect by virtue of which the one being of each kind that alone really exists, manifests itself to us as a plurality of homogeneous beings, always being originated anew and passing away in endless succession. The apprehension of things by means of and in accordance with this arrangement is immanent; on the other hand, that which is conscious of the true state of things is transcendental. We obtain this in abstracto through the Critique of Pure Reason, but in exceptional cases it can also appear intuitively. This last point is my own addition, which I am endeavouring to explain in the present third book.
If Kant’s teaching, and, since Kant’s time, that of Plato, had ever been properly understood and grasped; if men had truly and earnestly reflected on the inner meaning and content of the teachings of the two great masters, instead of lavishly using the technical expressions of the one and parodying the style of the other, they could not have failed long ago to discover how much the two great sages agree, and that the true significance, the aim, of both teachings is absolutely the same. Not only would they have refrained from constantly comparing Plato with Leibniz, on whom his spirit certainly did not rest, or even with a well-known gentleman still living,84 as if they wanted to mock at the manes of the great thinker of antiquity, but in general they would have gone much farther than they did, or rather would not have fallen behind so shamefully as they have done in the last forty years. They would not have allowed themselves to be led by the nose, today by one braggart tomorrow by another, and would not have opened with philosophical farces the nineteenth century that announced itself so importantly in Germany. These were performed over Kant’s grave (just as was done sometimes by the ancients at the funeral rites of their dead), and occasioned the well-merited ridicule of other nations, for such things least suit the serious and even solid German. But so small is the real public of genuine philosophers, that even followers who understand are brought to them only sparingly by the centuries. Eἰσὶ δὴ ναθηϰoϕóρoι μὲν πoλλoὶ, βάϰχoι δέγε παῦρoι. (Thyrsigeri quidem multi, Bacchi vero pauci.) ‛H ἀτιμíα ϕιλoσoϕíᾳ διὰ ταῦτα πρoσπέπτωϰεν, ὅτι oὐ ϰατ’ ἀξíαν αὐτὴς ἅπτoνται· oὐ γὰρ νóθoυς ἒδει ἅπτεσθαι, ἀλλὰ γνησíoυς. (Eam ob rem philosophia in infamiam incidit, quod non pro dignitate ipsam attingunt: neque enim a spuriis, sed a legitimis erat attrectanda,) Plato [Republic, 535 C].85
Men followed words, such words as “representations a priori,” “forms of perceiving and thinking known independently of experience,” “primary concepts of the pure understanding,” and so on. They now asked whether Plato’s Ideas, which were also primary concepts and which, moreover, were supposed to be reminiscences from a prenatal perception of truly existing things, were in some way the same thing as Kant’s forms of intuition and thought, residing a priori in our consciousness. As there was a slight resemblance in the expression of these two entirely different doctrines, the Kantian doctrine of forms, limiting the knowledge of the individual to the phenomenon, and the Platonic doctrine of Ideas, the knowledge of which expressly denies those very forms, these doctrines, in this respect diametrically opposite, were carefully compared, and men deliberated and disputed over their identity. Ultimately, they found that they were not the same, and concluded that Plato’s doctrine of Ideas and Kant’s critique of reason had no agreement at all. But enough of this.86