The World as Will and Idea (Vol. 1-3). Arthur Schopenhauer

from such a perception only in degree. Every one of these great discoveries is therefore, just like perception, an operation of the understanding, an immediate intuition, and as such the work of an instant, an apperçu, a flash of insight. They are not the result of a process of abstract reasoning, which only serves to make the immediate knowledge of the understanding permanent for thought by bringing it under abstract concepts, i.e., it makes knowledge distinct, it puts us in a position to impart it and explain it to others. The keenness of the understanding in apprehending the causal relations of objects which are known indirectly, does not find its only application in the sphere of natural science (though all the discoveries in that sphere are due to it), but it also appears in practical life. It is then called good sense or prudence, as in its other application it is better called acuteness, penetration, sagacity. More exactly, good sense or prudence signifies exclusively understanding at the command of the will. But the limits of these conceptions must not be too sharply defined, for it is always that one function of the understanding by means of which all animals perceive objects in space, which, in its keenest form, appears now in the phenomena of nature, correctly inferring the unknown causes from the given effects, and providing the material from which the reason frames general rules as laws of nature; now inventing complicated and ingenious machines by adapting known causes to desired effects; now in the sphere of motives, seeing through and frustrating intrigues and machinations, or fitly disposing the motives and the men who are susceptible to them, setting them in motion, as machines are moved by levers and wheels, and directing them at will to the accomplishment of its ends. Deficiency of understanding is called stupidity. It is just dulness in applying the law of causality, incapacity for the immediate apprehension of the concatenations of causes and effects, motives and actions. A stupid person has no insight into the connection of natural phenomena, either when they follow their own course, or when they are intentionally combined, i.e., are applied to machinery. Such a man readily believes in magic and miracles. A stupid man does not observe that persons, who apparently act independently of each other, are really in collusion; he is therefore easily mystified, and outwitted; he does not discern the hidden motives of proffered advice or expressions of opinion, &c. But it is always just one thing that he lacks—keenness, rapidity, ease in applying the law of causality, i.e., power of understanding. The greatest, and, in this reference, the most instructive example of stupidity I ever met with, was the case of a totally imbecile boy of about eleven years of age, in an asylum. He had reason, because he spoke and comprehended, but in respect of understanding he was inferior to many of the lower animals. Whenever I visited him he noticed an eye-glass which I wore round my neck, and in which the window of the room and the tops of the trees beyond were reflected: on every occasion he was greatly surprised and delighted with this, and was never tired of looking at it with astonishment, because he did not understand the immediate causation of reflection.

      While the difference in degree of the acuteness of the understanding, is very great between man and man, it is even greater between one species of animal and another. In all species of animals, even those which are nearest to plants, there is at least as much understanding as suffices for the inference from the effect on the immediate object, to the indirectly known object as its cause, i.e., sufficient for perception, for the apprehension of an object. For it is this that constitutes them animals, as it gives them the power of movement following on motives, and thereby the power of seeking for food, or at least of seizing it; whereas plants have only movement following 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