(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_.