For the objective consideration the brain is the efflorescence of the organism; therefore only where the latter has attained its highest perfection and complexity does the brain appear in its greatest development. But in the preceding chapter we have recognised the organism as the objectification of the will; therefore the brain also, as a part of it, must belong to this objectification. Further, from the fact that the organism is only the visibility of the will, thus in itself is the will, I have deduced that every affection of the organism at once and directly affects the will, i. e., is felt as agreeable or painful. Yet, with the heightening of sensibility, in the higher development of the nervous system, the possibility arises that in the nobler, i. e., the objective, organs of sense (sight and hearing) the exquisitely delicate affections proper to them are perceived without in themselves and directly affecting the will, that is, without being either painful or agreeable, and that therefore they appear in consciousness as indifferent, merely perceived, sensations. But in the brain this heightening of sensibility reaches such a high degree that upon received impressions of sense a reaction even takes place, which does not proceed directly from the will, but is primarily a spontaneity of the function of understanding, which makes the transition from the directly perceived sensation of the senses to its cause; and since the brain then at once produces the form of space, there thus arises the perception of an external object. We may therefore regard the point at which the understanding makes the transition from the mere sensation upon the retina, which is still a mere affection of the body and therefore of the will, to the cause of that sensation, which it projects by means of its form of space, as something external and different from its own body, as the boundary between the world as will and the world as idea, or as the birthplace of the latter. In man, however, the spontaneity of the activity of the brain, which in the last instance is certainly conferred by the will, goes further than mere perception and immediate comprehension of causal relations. It extends to the construction of abstract conceptions out of these perceptions, and to operating with these conceptions, i. e., to thinking, as that in which his reason consists. Thoughts are therefore furthest removed from the affections of the body, which, since the body is the objectification of the will, may, through increased intensity, pass at once into pain, even in the organs of sense. Accordingly idea and thought may also be regarded as the efflorescence of the will, because they spring from the highest perfection and development of the organism; but the organism, in itself and apart from the idea, is the will. Of course, in my explanation, the existence of the body presupposes the world of idea; inasmuch as it also, as body or real object, is only in this world; and, on the other hand, the idea itself just as much presupposes the body, for it arises only through the function of an organ of the body. That which lies at the foundation of the whole phenomenon, that in it which alone has being in itself and is original, is exclusively the will; for it is the will which through this very process assumes the form of the idea, i. e., enters the secondary existence of an objective world, or the sphere of the knowable. Philosophers before Kant, with few exceptions, approached the explanation of the origin of our knowledge from the wrong side. They set out from a so-called soul, an existence whose inner nature and peculiar function consisted in thinking, and indeed quite specially in abstract thinking, with mere conceptions, which belonged to it the more completely the further they lay from all perception. (I beg to refer here to the note at the end of § 6 of my prize essay on the foundation of morals.) This soul has in some inconceivable manner entered the body, and there it is only disturbed in its pure thinking, first by impressions of the senses and perceptions, still more by the desires which these excite, and finally by the emotions, nay, passions, to which these desires develop; while the characteristic and original element of this soul is mere abstract thinking, and given up to this it has only universals, inborn conceptions, and æternæ veritates for its objects, and leaves everything perceptible lying far below it. Hence, also, arises the contempt with which even now “sensibility” and the "sensuous" are referred to by professors of philosophy, nay, are even made the chief source of immorality, while it is just the senses which are the genuine and innocent source of all our knowledge, from which all thinking must first borrow its material, for in combination with the a priori functions of the intellect they produce the perception. One might really suppose that in speaking of sensibility these gentlemen always think only of the pretended sixth sense of the French. Thus, as we have said, in the process of knowledge, its ultimate product was made that which is first and original in it, and accordingly the matter was taken hold of by the wrong end. According to my exposition, the intellect springs from the organism, and thereby from the will, and hence could not be without the latter. Thus, without the will it would also find no material to occupy it; for everything that is knowable is just the objectification of the will.

But not only the perception of the external world, or the consciousness of other things, is conditioned by the brain and its functions, but also self-consciousness. The will in itself is without consciousness, and remains so in the greater part of its phenomena. The secondary world of idea must be added, in order that it may become conscious of itself, just as light only becomes visible through the bodies which reflect it, and without them loses itself in darkness without producing any effect. Because the will, with the aim of comprehending its relations to the external world, produces a brain in the animal individual, the consciousness of its own self arises in it, by means of the subject of knowledge, which comprehends things as existing and the ego as willing. The sensibility, which reaches its highest degree in the brain, but is yet dispersed through its different parts, must first of all collect all the rays of its activity, concentrate them, as it were, in a focus, which, however, does not lie without, as in the case of the concave mirror, but within, as in the convex mirror. With this point now it first describes the line of time, upon which, therefore, all that it presents to itself as idea must exhibit itself, and which is the first and most essential form of all knowledge, or the form of inner sense. This focus of the whole activity of the brain is what Kant called the synthetic unity of apperception (cf. vol. ii. p. 475). Only by means of this does the will become conscious of itself, because this focus of the activity of the brain, or that which knows, apprehends itself as identical with its own basis, from which it springs, that which wills; and thus the ego arises. Yet this focus of the brain activity remains primarily a mere subject of knowledge, and as such capable of being the cold and impartial spectator, the mere guide and counsellor of the will, and also of comprehending the external world in a purely objective manner, without reference to the will and its weal or woe. But whenever it turns within, it recognises the will as the basis of its own phenomenon, and therefore combines with it in the consciousness of an ego. That focus of the activity of the brain (or the subject of knowledge) is indeed, as an indivisible point, simple, but yet is not on this account a substance (soul), but a mere condition or state. That of which it is itself a condition or state can only be known by it indirectly, as it were through reflection. But the ceasing of this state must not be regarded as the annihilation of that of which it is a state. This knowing and conscious ego is related to the will, which is the basis of its phenomenal appearance, as the picture in the focus of a concave mirror is related to the mirror itself, and has, like that picture, only a conditioned, nay, really a merely apparent, reality. Far from being the absolutely first (as, for example, Fichte teaches), it is at bottom tertiary, for it presupposes the organism, and the organism presupposes the will. I admit that all that is said here is really only an image and a figure, and in part also hypothetical; but we stand at a point to which thought can scarcely reach, not to speak of proof. I therefore request the reader to compare with this what I have adduced at length on this subject in chapter 20.

Now, although the true being of everything that exists consists in its will, and knowledge together with consciousness are only added at the higher grades of the phenomenon as something secondary, yet we find that the difference which the presence and the different degree of consciousness places between one being and another is exceedingly great and of important results. The subjective existence of the plant we must think of as a weak analogue, a mere shadow of comfort and discomfort; and even in this exceedingly weak degree the plant knows only of itself, not of anything outside of it. On the other hand, even the lowest animal standing next to it is forced by increased and more definitely specified wants to extend the sphere of its existence beyond the limits of its own body. This takes place through knowledge. It has a dim apprehension of its immediate surroundings, out of which the motives for its action with a view to its own maintenance arise. Thus accordingly the medium of motives appears, and this is – the world existing objectively in time and space, the world as idea, however weak, obscure, and dimly dawning this first and lowest example of it may be. But it imprints itself ever more and more distinctly, ever wider and deeper, in proportion as in the ascending scale of animal organisations the brain is ever more perfectly produced. This progress in the development of the brain, thus of the intellect, and of the clearness of the idea, at each of these ever higher grades is, however, brought about by the constantly increasing and more complicated wants of this phenomenon of the will. This must always first afford the occasion for it, for without necessity nature (i. e., the will which objectifies itself in it) produces nothing, least of all the hardest of its productions – a more perfect brain: in consequence of its lex parsimoniæ: natura nihil agit frustra et nihil facit supervacaneum. It has provided every animal with the organs which are necessary for its sustenance and the weapons necessary for its conflict, as I have shown at length in my work, “Ueber den Willen in der Natur,” under the heading, “Vergleichende Anatomie.” According to this measure, therefore, it imparts to each the most important of those organs concerned with what is without, the brain, with its function the intellect. The more complicated, through higher development, its organisation became, the more multifarious and specially determined did its wants also become, and consequently the more difficult and the more dependent upon opportunity was the provision of what would satisfy them. Thus there was needed here a wider range of sight, a more accurate comprehension, a more correct distinction of things in the external world, in all their circumstances and relations. Accordingly we see the faculty of forming ideas, and its organs, brain, nerves, and special senses, appear ever more perfect the higher we advance in the scale of animals; and in proportion as the cerebral system develops, the external world appears ever more distinct, many-sided, and complete in consciousness. The comprehension of it now demands ever more attention, and ultimately in such a degree that sometimes its relation to the will must momentarily be lost sight of in order that it may take place more purely and correctly. Quite definitely this first appears in the case of man. With him alone does a pure separation of knowing and willing take place. This is an important point, which I merely touch on here in order to indicate its position, and be able to take it up again later. But, like all the rest, nature takes this last step also in extending and perfecting the brain, and thereby in increasing the powers of knowledge, only in consequence of the increased needs, thus in the service of the will. What this aims at and attains in man is indeed essentially the same, and not more than what is also its goal in the brutes – nourishment and propagation. But the requisites for the attainment of this goal became so much increased in number, and of so much higher quality and greater definiteness through the organisation of man, that a very much more considerable heightening of the intellect than the previous steps demanded was necessary, or at least was the easiest means of reaching the end. But since now the intellect, in accordance with its nature, is a tool of the most various utility, and is equally applicable to the most different kinds of ends, nature, true to her spirit of parsimony, could now meet through it alone all the demands of the wants which had now become so manifold. Therefore she sent forth man without clothing, without natural means of protection or weapons of attack, nay, with relatively little muscular power, combined with great frailty and little endurance of adverse influences and wants, in reliance upon that one great tool, in addition to which she had only to retain the hands from the next grade below him, the ape. But through the predominating intellect which here appears not only is the comprehension of motives, their multiplicity, and in general the horizon of the aims infinitely increased, but also the distinctness with which the will is conscious of itself is enhanced in the highest degree in consequence of the clearness of the whole consciousness which has been brought about, which is supported by the capacity for abstract knowledge, and now attains to complete reflectiveness. But thereby, and also through the vehemence of the will, which is necessarily presupposed as the supporter of such a heightened intellect, an intensifying of all the emotions appears, and indeed the possibility of the passions