"A definite idea of distance, as well as of form and size, is only obtained by sight and touch, and by reflecting on the impressions made on both senses; but for this purpose we must take into account the muscular motion and voluntary locomotion of the individual.—Caspar Hauser, in a detailed account of his own experience in this respect, states, that upon his first liberation from confinement, whenever he looked through the window upon external objects, such as the street, garden, &c., it appeared to him as if there were a shutter quite close to his eye, and covered with confused colours of all kinds, in which he could recognise or distinguish nothing singly. He says farther, that he did not convince himself till after some time during his walks out of doors, that what had at first appeared to him as a shutter of various colours, as well as many other objects, were in reality very different things; and that at length the shutter disappeared, and he saw and recognised all things in their just proportions. Persons born blind who obtain their sight by an operation in later years only, sometimes imagine that all objects touch their eyes, and lie so near to them that they are afraid of stumbling against them; sometimes they leap towards the moon, supposing that they can lay hold of it; at other times they run after the clouds moving along the sky, in order to catch them, or commit other such extravagancies. Since ideas are gained by reflection upon sensation, it is further necessary in all cases, in order that an accurate idea of objects may be formed from the sense of sight, that the powers of the mind should be unimpaired, and undisturbed in their exercise. A proof of this is afforded in the instance related by Haslam,[84] of a boy who had no defect of sight, but was weak in understanding, and who in his seventh year was unable to estimate the distances of objects, especially as to height; he would extend his hand frequently towards a nail on the ceiling, or towards the moon, to catch it. It is therefore the judgment which corrects and makes clear this idea, or perception of visible objects."
The intellectual nature of perception as I have shown it, is corroborated physiologically by Flourens[85] as follows:
"Il faut faire une grand distinction entre les sens et l'intelligence. L'ablation d'un tubercule détermine la perte de la sensation, du sens de la vue; la rétine devient insensible, l'iris devient immobile. L'ablation d'un lobe cérébral laisse la sensation, le sens, la sensibilité de la rétine, la mobilité de l'iris; elle ne détruit que la perception seule. Dans un cas, c'est un fait sensorial; et, dans l'autre, un fait cérébral; dans un cas, c'est la perte du sens; dans l'autre, c'est la perte de la perception. La distinction des perceptions et des sensations est encore un grand résultat; et it est démontré aux yeux. Il y a deux moyens de faire perdre la vision par l'encéphale: 1° par les tubercules, c'est la perte du sens, de la sensation; 2° par les lobes, c'est la perte de la perception, de l'intelligence. La sensibilité n'est donc pas l'intelligence; penser n'est donc pas sentir; et voilà toute une philosophie renversée. L'idée n'est donc pas la sensation; et voilà encore une autre preuve du vice radical de cette philosophie." And again, p. 77, under the heading: Séparation de la Sensibilité et de la Perception:—"Il y a une de mes expériences qui sépare nettement la sensibilité de la perception. Quand on enlève le cerveau proprement dit (lobes ou hémisphères cérébraux) à un animal, l'animal perd la vue. Mais, par rapport a l'œil, rien n'est changé: les objets continuent à se peindre sur la rétine; l'iris reste contractile, le nerf optique sensible, parfaitement sensible. Et cependant l'animal ne voit plus; il n'y a plus vision, quoique tout ce qui est sensation subsiste; il n'y a plus vision, parce qu'il n'y a plus perception. Le percevoir, et non le sentir, est donc le premier élément de l'intelligence. La perception est partie de l'intelligence, car elle se perd avec l'intelligence, et par l'ablation du même organe, les lobes ou hémisphères cérébraux; et la sensibilité n'en est point partie, puisqu'elle subsiste après la perte de l'intelligence et l'ablation des lobes ou hémisphères."
The following famous verse of the ancient philosopher Epicharmus, proves that the ancients in general recognized the intellectual nature of perception: Νοῦς ὁρῇ καὶ νοῦς ἀκούει· τἆλλα κωφὰ καὶ τυφλά. (Mens videt, mens audit; cætera surda et cœca.)[86] Plutarch in quoting this verse, adds:[87] ὡς τοῦ περὶ τὰ ὄμματα καὶ ὦτα πάθους, ἂν μὴ παρῇ τὸ φρονοῦν, αἴσθησιν οὐ ποιοῦντος (quia affectio oculorum et aurium nullum affert sensum, intelligentia absente). Shortly before too he says: Στράτωνος τοῦ φυσικοῦ λόγος ἐστίν, ἀποδεικνύων ὡς οὐδ' αἰσθάνεσθαι τοπαράπαν ἄνευ τοῦ νοεῖν ὑπάρχει. (Stratonis physici exstat ratiocinatio, qua "sine intelligentia sentiri omnino nihil posse" demonstrat.)[88] Again shortly after he says: ὅθεν ἀνάγκη, πᾶσιν, οἷς τὸ αἰσθάνεσθαι, καὶ τὸ νοεῖν ὑπάρχειν, εἰ τῷ νοεῖν αἰσθάνεσθαι πεφύκαμεν (quare necesse est, omnia, quæ sentiunt, etiam intelligere, siquidem intelligendo demum sentiamus).[89] A second verse of Epicharmus might be connected with this, which is quoted by Diogenes Laertes (iii. 16):
Εὔμαιε, τὸ σοφόν ἐστιν οὐ καθ' ἓν μόνον,
ἀλλ' ὅσα περ ζῇ, πάντα καὶ γνώμαν ἔχει.
(Eumaee, sapientia non uni tantum competit, sed quæcunque vivunt etiam intellectum habent.) Porphyry likewise endeavours to show at length that all animals have understanding.[90]
Now, that it should be so, follows necessarily from the intellectual character of perception. All animals, even down to the very lowest, must have Understanding—that is, knowledge of the causal law, although they have it in very different degrees of delicacy and of clearness; at any rate they must have as much of it as is required for perception by their senses; for sensation without Understanding would be not only a useless, but a cruel gift of Nature. No one, who has himself any intelligence, can doubt the existence of it in the higher animals. But at times it even becomes undeniably evident that their knowledge of causality is actually à priori, and that it does not arise from the habit of seeing one thing follow upon another. A very young puppy will not, for instance, jump off a table, because he foresees what would be the consequence. Not long ago I had some large curtains put up at my bed-room window, which reached down to the floor, and were drawn aside from the centre by means of a string. The first morning they were opened I was surprised to see my dog, a very intelligent poodle, standing quite perplexed, and looking upwards and sidewards for the cause of the phenomenon: that is, he was seeking for the change which he knew à priori must have taken place. Next day the same thing happened again.—But even the lowest animals have perception—consequently Understanding—down to the aquatic polypus, which has no distinct organs of sensation, yet wanders from leaf to leaf on its waterplant, while clinging to it with its feelers, in search of more light.
Nor is there, indeed, any difference, beyond that of degree, between this lowest Understanding and that of man, which we however distinctly separate from his Reason. The intermediate gradations are occupied by the various series of animals, among which the highest, such as the monkey, the elephant, the dog, astonish us often by their intelligence. But in every case the business of the Understanding is invariably to apprehend directly causal relations: first, as we have seen, those between our own body and other bodies, whence proceeds objective perception; then those between these objectively perceived bodies among themselves, and here, as has been shown in § 20, the causal relation manifests itself in three forms—as cause, as stimulus, and as motive. All movement in the world takes place according to these three forms of the causal relation, and through them alone does the intellect comprehend it. Now, if, of these three, causes, in the narrowest sense of the word, happen to be the object of investigation for the Understanding, it will produce Astronomy, Mechanics, Physics, Chemistry, and will invent machines for good and for evil; but in all cases a direct, intuitive apprehension of the causal connection will in the last resort lie at the bottom of all its discoveries. For the sole form and function of the Understanding is this apprehension, and not by any means the complicated machinery of Kant's twelve Categories, the nullity of which I have proved.—(All comprehension is a direct, consequently intuitive, apprehension of the causal connection; although this has to be reduced at once to abstract conceptions in order to be fixed. To calculate therefore, is not to understand, and, in itself, calculation conveys no comprehension of things. Calculation deals exclusively with abstract conceptions of magnitudes, whose mutual relations it determines. By it we never attain the slightest comprehension of a physical process, for this requires intuitive comprehension of space-relations, by means of which causes take effect. Calculations have merely practical, not theoretical, value. It may even be said that where calculation begins, comprehension ceases; for a brain occupied with numbers is, as long as it calculates, entirely estranged from the causal connection in physical processes, being engrossed in purely abstract, numerical conceptions. The result, however, only shows us how much, never what. "L'expérience et le calcul," those watchwords of French physicists, are not therefore by any means adequate [for thorough insight].)—If, again, stimuli are the guides of the Understanding, it will produce Physiology of Plants and Animals, Therapeutics, and Toxicology. Finally, if it devotes itself to the study of motives, the Understanding will use them, on the one hand, theoretically, to guide it in producing works on Morality, Jurisprudence, History, Politics, and even Dramatic and Epic Poetry; on the other hand, practically, either merely to train animals, or for the higher purpose of making human beings dance to its music, when once it has succeeded in discovering which particular wire has to be pulled in order to move each puppet at its pleasure. Now, with reference to the function which effects this, it is quite immaterial whether the intellect turns gravitation ingeniously to account, and makes it serve its purpose by stepping in just at the right time, or whether it brings the collective or the individual propensities of men into play for its own ends. In its practical application we call the Understanding shrewdness or, when used to outwit others, cunning; when its aims are very insignificant, it is called slyness and, if combined with injury to others, craftiness. In its purely theoretical application, we call it simply Understanding, the higher degrees of which are named acumen, sagacity, discernment, penetration, while its lower degrees are termed dulness, stupidity, silliness, &c. &c. These widely differing degrees of sharpness are innate, and cannot be acquired; although, as I have already shown, even in the earliest stages of the application of the Understanding, i.e. in empirical perception, practice and knowledge of the material to which it is applied, are needed. Every simpleton has Reason—give him the premisses, and he will draw the conclusion; whereas primary, consequently intuitive, knowledge is supplied by the Understanding: herein lies the difference. The pith of every great discovery, of every plan having universal historical importance, is accordingly the product of a happy moment in which, by a favourable coincidence of outer and inner circumstances, some complicated causal series, some hidden causes of phenomena which had been seen thousands of times before, or some obscure, untrodden paths, suddenly reveal themselves to the intellect.—
By the preceding explanations of the processes in seeing and feeling, I have incontestably shown that empirical perception is essentially the work of the Understanding, for which the material only is supplied by the senses in sensation—and a poor material it is, on the whole; so that the Understanding is, in fact, the artist, while the senses are but the under-workmen who hand it the materials. But the process consists throughout in referring from given effects to their causes, which by this process are enabled to present themselves as objects in Space. The very fact that we presuppose Causality in this process, proves precisely that this law must have been supplied by the Understanding itself; for it could never have found its way into the intellect from outside. It is indeed the first condition of all empirical perception; but this again is the form in which all external experience presents itself to us; how then can this law of Causality be derived from experience, when it is itself essentially presupposed by experience?—It was just because of the utter impossibility of this, and because Locke's philosophy had put an end to all à priority, that Hume denied the whole reality of the conception of Causality. He had besides already mentioned two false hypotheses in the seventh section of his "Inquiry concerning the Human Understanding," which recently have again been advanced: the one, that the effect of the will upon the members of our body; the other, that the resistance opposed to our pressure by outward objects, is the origin and prototype of the conception of Causality. Hume refutes both in his own way and according to his own order of ideas. I argue as follows. There is no causal connection whatever between acts of the will and actions of the body; on the contrary, both are immediately one and the same thing, only perceived in a double aspect—that is, on the one hand, in our self-consciousness, or inner sense, as acts of the will; on the other, simultaneously in exterior, spacial brain-perception, as actions of the body.[91] The second hypothesis is false, first because, as I have already shown at length, a mere sensation of touch does not yet give any objective perception whatever, let alone the conception of Causality, which never can arise from the feeling of an impeded muscular effort: besides impediments of this kind often occur without any external cause; secondly, because our pressing against an external object necessarily has a motive, and this already presupposes apprehension of that object, which again presupposes knowledge of Causality.—But the only means of radically proving the conception of Causality to be independent of all experience was by showing, as I have done, that the whole possibility of experience is conditioned by the conception of Causality. In § 23 I intend to show that Kant's proof, propounded with a similar intent, is false.