law; the function of the lawgiver is to connect public and personal welfare by means of rewards and punishments, and thus to elevate morality.  A man is called virtuous when his stronger passions harmonize with the general interest.  Unfortunately the virtues of prejudice, which do not contribute to the public good, are more honored among most nations than the political virtues, to which alone real merit belongs.  And self-interest is always the one motive to just and generous action; we serve only our own interests in furthering the welfare of the community.  As the promulgator of these doctrines was himself a kind and generous man, Rousseau could make to him the apt reply:  You endeavor in vain to degrade yourself below your own level; your spirit gives evidence against your principles; your benevolent heart discredits your doctrines.

The morality of enlightened self-love or “intelligent self-interest” appears in a milder form in Maupertuis (Works, 1752), and Frederick the Great,[1] to the latter of whom D’Alembert objected by letter that interest could never generate the sense of duty and reverence for the law.

[Footnote 1:  Essay on Self-love as a Principle of Morals, 1770, printed in the proceedings of the Academy of Sciences.  Cf. on Frederick, Ed. Zeller, 1886.]

%3.  Skepticism and Materialism.%

The ideas thus far developed move in a direction whose further pursuit inevitably issues in materialism.  Diderot, the editor of the Encyclopedia of the Sciences, Arts, and Trades (1751-72), which gathered all the currents of the Illumination into one great stream and carried them to the open sea of popular culture, reflects in his intellectual development the dialectical movement from deism through skepticism to atheism and materialism, and was a co-laborer in the work which brought the whole movement to a conclusion, Holbach’s System of Nature.  Two decades, however, before the latter work, the outcome of a long development of thought, appeared, the physician La Mettrie[1] (1709-51) had promulgated materialism, though rather in an anthropological form than as a world-system, and with cynical satisfaction in the violation of traditional beliefs—­in his Natural History of the Soul, 1745, in a disguised form, and, undisguised, in his Man a Machine, 1748—­and at the same time (Anti-Seneca, or Discourse on Happiness, 1748) had sketched out for Helvetius the outlines of the sensationalistic morality of interest.  While ill with a violent fever he observed the influence of the heightened circulation of the blood on his mental tone, and inferred that thought is the result of the bodily organization.  The soul can only be known from the body.  The senses, the best philosophers, teach us that matter is never without form and motion; and whether all matter is sentient or not, certainly all that is sentient is material, and every part of the organism contains a vital principle (the heart of a frog beats for an