A being, whatever it may be, whether vague and almost amorphous or clearly defined, is not isolated in the universal vital environment. It is the molecule of a diapason. It vibrates, not of its own accord, but in obedience to a general movement. The living cell, itself in internal movement and subjected to all the reactions of external movement, perceives this movement doubtless as an unique impression only. But when several cells come together and live in permanent contact, the impressions of external movement begin to be perceived as differentiated. Is this then necessary? Do there then already exist luminous vibrations, different from sonorous vibrations? Assuredly, since otherwise the sensorial differentiation would be inexplicable, being useless. The union of several cells permits the animal to divide its work of perception, and to present to each perceptible manifestation an organ or, at least, the sketch of an organ, appropriate to receive it.
It would be possible, it is true, from the idealistic point of view, to suppose that the senses are a creation of the individual, an enhancement of his own life, and that he differentiates, on his own initiative, his cinematic impression. This would be a phenomenon of spontaneous analytic creation, the analyzing instrument existing prior to the matter analyzed, or even, for exasperated idealists, creating this matter according to determinate needs, once and for all, by its own physiology. It would then be a property of organized living matter to fabricate senses for itself, and to diversify, by this means, its own life. This point of view is not easy to admit for several reasons, purely physical.
First, if this sensorial differentiation were a faculty of living matter, it would not be observed to be limited in its powers, as it is. Even admitting certain senses unknown to man, such as the chemical sense, the electric sense, the sense of orientation (extremely doubtful), it is still seen that the number of senses is very limited. But, far more important, the fundamental senses are found to be identical among the majority of the higher species, vertebrates and insects, with very few exceptions. The moment the animal arrives at sensorial differentiation, this differentiation occurs in response to the manifestations of matter.
The senses should, then, correspond to external realities. They have been created, not by the perceiving being, but by the perceptible environment. It is the light that has created the eye, just as, in our houses, it has created the windows. Where there is no light, fish become blind. This is perhaps the direct proof, for if light is the creation of the eye, this creation can occur at the bottom of the sea quite as well as on the surface of the earth. Another proof: these same fish, having become blind, but still requiring a luminous habitat, create for themselves in the night of the abysses, not eyes, but apparatus directly productive of light; and this artificial light creates anew the atrophied eye. The senses are then clearly the product of the environment. That is all they can do, moreover, their utility being nil, if the environment is not perceptible. It might still be objected that it is the nervous system which, having intuition of an environment to be perceived, creates for itself organs adapted to this perception. But this is merely begging the question; for, either the nervous system has knowledge of the external environment, which means that it already has senses, or else it has no senses, and thus can have no knowledge. A more serious objection would be that, sensorial aptitude being a property of the nervous system, it would afterwards create for itself organs in order to perceive more distinctly, and clearly differentiated, the various natural phenomena. This view would explain up to a certain point the creation of sensorial organs, but not the existence of the senses themselves as sensitive power. It is, moreover, certain that the nervous system acts rather by tyrannizing the organs at its disposal, than by seeking to modify these organs or to create new ones. It is a power which evidently exceeds the limits of its capacity. It has, on the contrary, devolved upon the external phenomena which, in acting mechanically on the living matter, produce in it local modifications. The organs of the senses seem to be nothing other than surfaces sensitized by the very agents which, once their work is done, will reflect in them their particular physiognomy. The eye—let us take once more this example, and repeat it—is a creation of light.
Since they are themselves the work of the principal general phenomena, the senses ought then to agree exactly—allowing for approximation—with the very nature which has created them. The luminous environment is not, in this case, a dream, but a reality, and a reality existing prior to the eye which perceives it; and, since the eye is the very product of light, objects situated in this luminous environment should be perceived by it as an exact image, just as the drill which creates a hole, creates it strictly to its size, its form, its image. Bacon said that the senses are holes. Here this is only a metaphor.
IV
There remains the question of the co-ordination of the impressions received materially by the senses. This co-ordination, for elementary sensations, is evidently identical for all beings. The snail, his horn being threatened, and man, his eye, make the same shrinking movement. Identical acts can have as cause only identical realities, or ones perceived as such. With judgment, we enter upon the mystery. If light is constant, the judgment which admits its existence is variable according to the species, and, in the higher species, according to the individual. It is clear that all eyes are affected by light, but we do not know to what degree, or according to what mode of spectral decomposition. It is the same for all other senses. Even if the reality of the sensible world be admitted, we are obliged to pronounce cautiously upon the quality of this reality, as reality perceived and judged. We then return to idealism, though having had a quite different end in view. We must retrace our steps, contemplate anew the ironic portress, and resign ourselves never to know anything save appearance.
Another fact, however, remains—another fortress, perhaps, reared facing the other. This is, that matter existed before life. The gain seems slight, but it is equivalent to saying that the phenomena perceived by the senses are exterior to the senses which now perceive them; and this perhaps means that, if life becomes extinct, matter will survive life. The proposition of the idealists that the world would come to an end if there were no longer any sensibilities capable of feeling it, any intelligences capable of perceiving it, seems, therefore, untenable. And yet what would a world be, that was neither thought nor felt? We must recognize this, that when we think of a world void of thought, it still contains our thought, or it is our thought which contains it and animates it. Another phenomenon analogous to this has, perhaps, contributed much to belief in the immortality of the soul, namely, that we cannot conceive of ourselves as dead save by thinking of this death, by feeling and seeing it. The idea of our non-existence supposes, moreover, the life of our thought. That there is here an illusion due to the very functioning of the mechanism of thought is probable enough; but it is difficult not to take it into account. It would seem somewhat high-handed to make abstraction of it.
We can attempt it, however, and try a new road leading "beyond thought." The way would be to consider the general movement of the things in which our thought itself is closely implicated, and by which it is rigorously conditioned. Far, perhaps, from thought thinking life, it is life that animates thought. What is anterior is a vast rhythmic undulation, of which thought is but one of the moments, one of the bounds.
The position taken by man outside the world to judge the world, is a factitious attitude. It is, perhaps, only a game, and one that is too easy. The division of man into two parts, thought, physical being, one considering the other and pretending to contain it, is only a philosophic amusement which becomes impossible the moment we stop to consider. There is, in fact, a physic of thought. We know that it is a product, measurable, ponderable. Unformulated externally, it nevertheless manifests its physical existence by the weight which it imposes upon the nervous system. It needs speech, writing, or some sort of sign, in order to manifest itself externally. Telepathy, thought, penetration, presentiment—if there be any facts in this category which have really been verified—would in such a case be so many proofs of the materiality of thought. But it is useless to multiply arguments in favour of a fact which is no longer contested save by theology.