5. The Systéme de la Nature afterwards attempted to elaborate with greater earnestness and scientific precision, that which had been uttered so superficially and so superciliously by La Mettrie, viz., the doctrine that matter alone exists, while mind is nothing other than matter refined.
The Systéme de la Nature appeared in London under a fictitious name in 1770. It was then published as a posthumous work of Mirabaud, late secretary of the Academy. It doubtless had its origin in the circle which was wont to assemble with Baron Holbach, and of which Diderot, Grimm, and others formed a part. Whether the Baron Holbach himself, or his tutor Lagrange is the author of this work, or whether it is the joint production of a number, cannot now be determined. The Systéme de la Nature is hardly a French book: the style is too heavy and tedious.
There is, in fact, nothing but matter and motion, says this work. Both are inseparably connected. If matter is at rest, it is only because hindered in motion, for in its essence it is not a dead mass. Motion is twofold, attraction and repulsion. The different motions which we see are the product of these two, and through these different motions arise the different connections and the whole manifoldness of things. The laws which direct in all this are eternal and unchangeable.—The most weighty consequences of such a doctrine are:
(1.) The materiality of man. Man is no twofold being compounded of mind and matter, as is erroneously believed. If the inquiry is closely made what the mind is, we are answered, that the most accurate philosophical investigations have shown, that the principle of activity in man is a substance whose peculiar nature cannot be known, but of which we can affirm that it is indivisible, unextended, invisible, &c. But now, who should conceive any thing determinate in a substance which is only the negation of that which gives knowledge, an idea which is peculiarly only the absence of all ideas? Still farther, how can it be explained upon such a hypothesis, that a substance which itself is not material can work upon material things; and how can it set these in motion, since there is no point of contact between the two? In fact, those who distinguish their soul from their body, have only to make a distinction between their brain and their body. Thought is only a modification of our brain, just as volition is another modification of the same bodily organ.
(2.) Another chimera, the belief in the being of a God, is connected with the twofold division of man into body and soul. This belief arises like the hypothesis of a soul-substance, because mind is falsely divided from matter, and nature is thus made twofold. The evil which men experienced, and whose natural cause they could not discover, they assigned to a deity which they imagined for the purpose. The first notions of a God have their source therefore in sorrow, fear, and uncertainty. We tremble because our forefathers for thousands of years have done the same. This circumstance awakens no auspicious prepossession. But not only the rude, but also the theological idea of God is worthless, for it explains no phenomenon of nature. It is, moreover, full of absurdities, for, since it ascribes moral attributes to God, it renders him human; while on the other hand, by a mass of negative attributes, it seeks to distinguish him absolutely from every other being. The true system, the system of nature, is hence atheistic. But such a doctrine requires a culture and a courage which neither all men nor most men possess. If we understand by the word atheist one who considers only dead matter, or who designates the moving power in nature with the name God, then is there no atheist, or whoever would be one is a fool. But if the word means one who denies the existence of a spiritual being, a being whose attributes can only be a source of annoyance to men, then are there indeed atheists, and there would be more of them, if a correct knowledge of nature and a sound reason were more widely diffused. But if atheism is true, then should it be diffused. There are, indeed, many who have cast off the yoke of religion, who nevertheless think it is necessary for the common people in order to keep them within proper limits. But this is just as if we should determine to give a man poison lest he should abuse his strength. Every kind of Deism leads necessarily to superstition, since it is not possible to continue on the standpoint of pure deism.
(3.) With such premises the freedom and immortality of the soul both disappear. Man, like every other substance in nature, is a link in the chain of necessary connection, a blind instrument in the hands of necessity. If any thing should be endowed with self-motion, that is, with a capacity to produce motion without any other cause, then would it have the power to destroy motion in the universe; but this is contrary to the conception of the universe, which is only an endless series of necessary motions spreading out into wider circles continually. The claim of an individual immortality is absurd. For to affirm that the soul exists after the destruction of the body, is to affirm that a modification of a substance can exist after the substance itself has disappeared. There is no other immortality than to live in the remembrance of posterity.
(4.) The practical consequences of these principles are in the highest degree favorable for the system of nature, the utility of any doctrine being ever the first criterion of its truth. While the ideas of theologians are productive only of disquiet and anxiety to man, the system of nature frees him from all such unrest, teaches him to enjoy the present moment, and to quietly yield to his destiny, while it gives him that kind of apathy which every one must regard as a blessing. If morality would be active, it can rest only upon self-love and self-interest; it must show man whither his well-considered interest would lead him. He is a good man who gains his own interest in such a way that others will find it for their interest to assist him. The system of self-interest, therefore, demands the union of men among each other, and hence we have true morality.
The logical dogmatic materialism of the Système de la Nature is the farthest limit of an empirical direction in philosophy, and consequently closes that course of the development of a one-sided realism which had begun with Locke. The attempt first made by Locke to explain and derive the ideal world from the material, ended in materialism with the total reduction of every thing spiritual to the material, with the total denial of the spiritual. We must now, before proceeding farther, according to the classification made § XXVII., consider the idealistic course of development which ran parallel with the systems of a partial realism. At the head of this course stands Leibnitz.