I ask permission to reproduce here a communication made by me in December 1904 to the Société Française de Philosophie. I there set forth briefly the ideas which I have just developed in this book. This succinct exposé may be useful as a recapitulation of the argument.
Description of Matter.—The physicists who are seeking for a conception of the Inmost structure of matter in order to explain the very numerous phenomena they perceive, fancy they can connect them with other phenomena, less numerous, but of the same order. They thus consider matter in itself.
We psychologists add to matter something more, viz. the observer. We consider matter and define it by its relations to our modes of knowledge—that is to say, by bearing in mind that it is conditioned by our external perception. These are two different points of view.
In developing our own standpoint, we note that of the outer world we are acquainted with nothing but our sensations: if we propound this limit, it is because many observations and experiments show that, between the external object and ourselves, there is but one intermediary, the nervous system, and that we only perceive the modifications which the external object, acting as an excitant, provokes in this system.
Let us provisionally apply to these modifications the term sensations, without settling the question of their physical or mental nature.
Other experiments, again, prove to us that our sensations are not necessarily similar to the objects which excite them; for the quality of each sensation depends on what is called the specific energy of the nerve excited. Thus, whether the optic nerve be appealed to by a ray of light, an electric current, or a mechanical shock, it always gives the same answer, and this answer is the sensation of light.
It follows that our nervous system itself is only known to us as regards its structure by the intermediary of sensations, and we are not otherwise more informed upon its nature than upon that of any other object whatever.
In the second place, a much more serious consequence is that all our sensations being equally false, so far as they are copies of the excitants which provoke them, one has no right to use any of these sensations to represent to ourselves the inmost structure of matter. The theories to which many physicists still cling, which consist in explaining all the modalities of matter by different combinations of movement, start from false premises. Their error consists in explaining the whole body of our sensations by certain particular sensations of the eye, of the touch, and of the muscular sense, in which analysis discovers the elements and the source of the representation of motion. Now these particular sensations have no more objective value than those of the tongue, of the nose, and of the ear; in so far as they are related to the external excitant of which it is sought to penetrate the inmost nature, one of them is as radically false as the other.
It is true that a certain number of persons will think to escape from our conclusion, because they do not accept our starting point. There exist, in fact, several systems which propound that the outer world is known to us directly without the intermediary of a tertium quid, that is, of sensation. In the first place, the spiritists are convinced that disembodied souls can remain spectators of terrestrial life, and, consequently, can perceive it without the interposition of organs. On the other hand, some German authors have recently maintained, by rather curious reasoning, that the specific energy of our nervous system does not transform the excitants, and that our sensations are the faithful copies of that which causes them. Finally, various philosophers, Reid, Hamilton, and, in our own days, the deep and subtle mind of M. Bergson, have proposed to admit that by direct comprehension we have cognisance of the objects without mystery and as they are. Let this be admitted. It will change nothing in our conclusions, and for the following reasons.
We have said that no kind of our sensations—neither the visual, the tactile, nor the muscular—permits us to represent to ourselves the inmost structure of matter, because all sensations, without exception, are false, as copies of material objects. We are now assured that we are mistaken, and that our sensations are all true—that is to say, are faithful copies of the objects. If all are true, it comes to the same thing as if all are false. If all are true, it is impossible to make any choice among them, to retain only the sensations of sight and touch, and to use them in the construction of a mechanical theory, to the exclusion of the others. For it is impossible for us to explain some by the others. If all are equally true, they all have the same right to represent the structure of matter, and, as they are irreconcilable, no theory can be formed from their synthesis.