At length Diderot concludes by a series of questions which he thinks that philosophers may perhaps count worthy of discussion. What is the difference, for example, between living matter and dead? Does the energy of a living molecule vary by itself, or according to the quantity, the quality, the forms of the dead or living matter with which it is united? We need not continue the enumeration, because Diderot himself suddenly brings them to an end with a truly admirable expression of his sense of how unworthy they are of the attention of serious men, who are able to measure the difference between a wise and beneficent use of intelligence, and a foolish and wasteful misuse of it. “When I turn my eyes,” he says, “to the works of men, and see the cities that are built on every side, all the elements yoked to our service, languages fixed, nations civilised, harbours constructed, lands and skies measured—then the world seems to me very old. When I find man uncertain as to the first principles of medicine and agriculture, as to the properties of the commonest substances, as to knowledge of the maladies that afflict him, as to the pruning of trees, as to the best form for the plough, then it seems as if the earth had only been inhabited yesterday. And if men were wise, they would at last give themselves up to such inquiries as bear on their wellbeing, and would not take the trouble to answer my futile questions for a thousand years at the very soonest; or perhaps, even, considering the very scanty extent that they occupy in space and time, they would never deign to answer them at all.”
II.
In 1769 Diderot composed three dialogues, of which he said that, with a certain mathematical memoir, they were the only writings of his own with which he was contented. The first is a dialogue between himself and D’Alembert; the second is D’Alembert’s Dream, in which D’Alembert in his sleep continues the discussion, while Mdlle. Lespinasse, who is watching by his bedside, takes down the dreamer’s words; in the third, Mdlle. Lespinasse and the famous physician, Bordeu, conclude the matter.[213] It is impossible, Diderot said to Mdlle. Voland, to be more profound and more mad: it is at once a supreme extravagance, and the most deep-reaching philosophy. He congratulated himself on the cleverness of placing his ideas in the mouth of a man who dreams, on the ground that we must often give to wisdom the air of madness, in order to secure admittance. Mdlle. Lespinasse was not so complacent. She made D’Alembert insist that the dialogue should be destroyed, and Diderot believed that he had burned the only existing copy. As a matter of fact, the manuscript was not published until 1830, when all the people concerned had long been reduced to dust. There are five or six pages, Diderot said to Mdlle. Voland, which would make your sister’s hair stand on end. A man may be much less squeamish than Mdlle. Voland’s sister, and still pronounce the imaginative invention of D’Alembert’s Dream, and the sequel, to be as odious as anything since the freaks of filthy Diogenes in his tub. Two remarks may be made on this strange production. First, Diderot never intended the dialogues for the public eye. He would have been as shocked as the Archbishop of Paris himself, if he had supposed that they would become accessible to everybody who knows how to read. Second, though they are in form the most ugly and disgusting piece in the literature of philosophy, they testify in their own way to Diderot’s sincerity of interest in his subject. Science is essentially unsparing and unblushing, and D’Alembert’s Dream plunged exactly into those parts of physiology which are least fit to be handled in literature. The attempt to give an air of polite comedy to functions and secretions must be pronounced detestable, in spite of the dialectical acuteness and force with which Diderot pressed his point.
It would be impossible, in a book not exclusively designed for a public of professors, to give a full account of these three dialogues. It is indispensable to describe their drift, because it is here that Diderot figures definitely as a materialist. Diderot was in no sense the originator of the French materialism of the eighteenth century. He was preceded by Maupertuis, by Robinet, and by La Mettrie; and we have already seen that when he composed the Thoughts on the Interpretation of Nature (1754), he did not fully accept Maupertuis’s materialistic thesis. Lange has shown that at a very early period in the movement the most consistent materialism was ready and developed, while such leaders of the movement as Voltaire and Diderot still leaned either on deism, or on a mixture of deism and scepticism.[214] The philosophy of D’Alembert’s Dream is definite enough, and far enough removed alike from deism and scepticism.
“The thinking man is like a musical instrument. Suppose a clavecin to have sensibility and memory, and then say whether it would not repeat of itself the airs that you have played on its keys. We are instruments endowed with sensibility and memory. Our senses are so many keys, pressed by the nature that surrounds them, and they often press one another; and this, according to my judgment, is all that passes in a clavecin organised as you and I are organised.
“There is only one substance in the world. The marble of the statue makes the flesh of the man, and conversely. Reduce a block of marble to impalpable powder; mix this powder with humus, or vegetable earth; knead them well together; water the mixture; let it rot for a year, two years—time does not count. In this you sow the plant, the plant nourishes the man, and hence the passage from marble to tissue.
“Do you see this egg? With that you overturn all the schools of theology and all the temples of the earth. It is an insensible mass before the germ is introduced into it; and, after the germ is introduced, there is still an insensible mass, for the germ itself is only an inert fluid. How does this mass pass to another organisation, to life, to sensibility? By heat. What will produce heat? Movement. What will be the successive effects of movement? First, an oscillating point, a thread that extends, the flesh, the beak, and so forth.”
Then follows the application of the same ideas to the reproduction of man—a region whither it is not convenient to follow the physiological inquirer. The result as to the formation of the organic substance in man is as unflinching as the materialism of Büchner.
But doctor, cries Mdlle. Lespinasse, what becomes of vice and virtue? Virtue, that word so holy in all languages, that idea so sacred among all nations?
Bordeu. We must transform it into beneficence, and its opposite into the idea of maleficence. A man is happily or unhappily born; people are irresistibly drawn on by the general torrent that conducts one to glory, the other to ignominy.