on stimuli, whose direct influence they must await, or else decay, for they cannot seek after them nor appropriate them. We marvel at the great sagacity of the most developed species of animals, such as the dog, the elephant, the monkey or the fox, whose cleverness has been so admirably sketched by Buffon. From these most sagacious animals, we can pretty accurately determine how far understanding can go without reason, i. e., abstract knowledge embodied in concepts. We could not find this out from ourselves, for in us understanding and reason always reciprocally support each other. We find that the manifestation of understanding in animals is sometimes above our expectation, and sometimes below it. On the one hand, we are surprised at the sagacity of the elephant, who, after crossing many bridges during his journey in Europe, once refused to go upon one, because he thought it was not strong enough to bear his weight, though he saw the rest of the party, consisting of men and horses, go upon it as usual. On the other hand, we wonder that the intelligent Orang-outangs, who warm themselves at a fire they have found, do not keep it alight by throwing wood on it; a proof that this requires a deliberation which is not possible without abstract concepts. It is clear that the knowledge of cause and effect, as the universal form of understanding, belongs to all animals a priori, because to them as to us it is the prior condition of all perception of the outer world. If any one desires additional proof of this, let him observe, for example, how a young dog is afraid to jump down from a table, however much he may wish to do so, because he foresees the effect of the weight of his body, though he has not been taught this by experience. In judging of the understanding of animals, we must guard against ascribing to it the manifestations of instinct, a faculty which is quite distinct both from understanding and reason, but the action of which is often very analogous to the combined action of the two. We cannot, however, discuss this here; it will find its proper place in the second book, when we consider the harmony or so-called teleology of nature: and the 27th chapter of the supplementary volume is expressly devoted to it.
Deficiency of understanding we call stupidity: deficiency in the application of reason to practice we shall recognise later as foolishness: deficiency of judgment as silliness, and lastly, partial or entire deficiency of memory as madness. But each of these will be considered in its own place. That which is correctly known by reason is truth, that is, an abstract judgment on sufficient grounds (Essay on the Principle of Sufficient Reason, § 29 and following paragraphs); that which is correctly known by understanding is reality, that is correct inference from effect on the immediate object to its cause. Error is opposed to truth, as deception of the reason: illusion is opposed to reality, as deception of the understanding. The full discussion of all this will be found in the first chapter of my essay on Light and Colour. Illusion takes place when the same effect may be attributed to two causes, of which one occurs very frequently, the other very seldom; the understanding having no data to decide which of these two causes operates in any particular case, – for their effects are exactly alike, – always assumes the presence of the commoner cause, and as the activity of the understanding is not reflective and discursive, but direct and immediate, this false cause appears before us as a perceived object, whereas it is merely illusion. I have explained in the essay referred to, how in this way double sight and double feeling take place if the organs of sense are brought into an unusual position; and have thus given an incontrovertible proof that perception exists only through and for the understanding. As additional examples of such illusions or deceptions of the understanding, we may mention the broken appearance of a stick dipped in water; the reflections in spherical mirrors, which, when the surface is convex appear somewhat behind it, and when the surface is concave appear a long way in front of it. To this class also belongs the apparently greater extension of the moon at the horizon than at the zenith. This appearance is not optical, for as the micrometre proves, the eye receives the image of the moon at the zenith, at an even greater angle of vision than at the horizon. The mistake is due to the understanding, which assumes that the cause of the feebler light of the moon and of all stars at the horizon is that they are further off, thus treating them as earthly objects, according to the laws of atmospheric perspective, and therefore it takes the moon to be much larger at the horizon than at the zenith, and also regards the vault of heaven as more extended or flattened out at the horizon. The same false application of the laws of atmospheric perspective leads us to suppose that very high mountains, whose summits alone are visible in pure transparent air, are much nearer than they really are, and therefore not so high as they are; for example, Mont Blanc seen from Salenche. All such illusions are immediately present to us as perceptions, and cannot be dispelled by any arguments of the reason. Reason can only prevent error, that is, a judgment on insufficient grounds, by opposing to it a truth; as for example, the abstract knowledge that the cause of the weaker light of the moon and the stars at the horizon is not greater distance, but the denser atmosphere; but in all the cases we have referred to, the illusion remains in spite of every abstract explanation. For the understanding is in itself, even in the case of man, irrational, and is completely and sharply distinguished from the reason, which is a faculty of knowledge that belongs to man alone. The reason can only know; perception remains free from its influence and belongs to the understanding alone.
§ 7. With reference to our exposition up to this point, it must be observed that we did not start either from the object or the subject, but from the idea, which contains and presupposes them both; for the antithesis of object and subject is its primary, universal and essential form. We have therefore first considered this form as such; then (though in this respect reference has for the most part been made to the introductory essay) the subordinate forms of time, space and causality. The latter belong exclusively to the object, and yet, as they are essential to the object as such, and as the object again is essential to the subject as such, they may be discovered from the subject, i. e., they may be known a priori, and so far they are to be regarded as the common limits of both. But all these forms may be referred to one general expression, the principle of sufficient reason, as we have explained in the introductory essay.
This procedure distinguishes our philosophical method from that of all former systems. For they all start either from the object or from the subject, and therefore seek to explain the one from the other, and this according to the principle of sufficient reason. We, on the contrary, deny the validity of this principle with reference to the relation of subject and object, and confine it to the object. It may be thought that the philosophy of identity, which has appeared and become generally known in our own day, does not come under either of the alternatives we have named, for it does not start either from the subject or from the object, but from the absolute, known through “intellectual intuition,” which is neither object nor subject, but the identity of the two. I will not venture to speak of this revered identity, and this absolute, for I find myself entirely devoid of all “intellectual intuition.” But as I take my stand merely on those manifestoes of the “intellectual intuiter” which are open to all, even to profane persons like myself, I must yet observe that this philosophy is not to be excepted from the alternative errors mentioned above. For it does not escape these two opposite errors in spite of its identity of subject and object, which is not thinkable, but only “intellectually intuitable,” or to be experienced by a losing of oneself in it. On the contrary, it combines them both in itself; for it is divided into two parts, firstly, transcendental idealism, which is just Fichte's doctrine of the ego, and therefore teaches that the object is produced by the subject, or evolved out of it in accordance with the principle of sufficient reason; secondly, the philosophy of nature, which teaches that the subject is produced little by little from the object, by means of a method called construction, about which I understand very little, yet enough to know that it is a process according to various forms of the principle of sufficient reason. The deep wisdom itself which that construction contains, I renounce; for as I entirely lack “intellectual intuition,” all those expositions which presuppose it must for me remain as a book sealed with seven seals. This is so truly the case that, strange to say, I have always been unable to find anything at all in this doctrine of profound wisdom but atrocious and wearisome bombast.
The systems starting from the object had always the whole world of perception and its constitution as their problem; yet the object which they take as their starting-point is not always this whole world of perception, nor its fundamental element, matter. On the contrary, a division of these systems may be made,