Anthropology is for Holbach essentially reduced to two problems, the deduction of thought from motion, and of morality from the physical tendency to self-preservation. The forces of the soul are no other than those of the body. All mental faculties develop from sensation; sensations are motions in the brain which reveal to us motions without the brain. All the passions may be reduced to love and hate, desire and aversion, and depend upon temperament, on the individual mixture of the fluid parts. Virtue is the equilibrium of the fluids. All human actions proceed from interest. Good and bad men are distinguished only by their organizations, and by the ideas they form concerning happiness. With the same necessity as that of the act itself, follow the love or contempt of fellow-men, the pleasure of self-esteem and the pain of repentance (regret for evil consequences, hence no evidence of freedom). Neither responsibility nor punishment is done away with by this necessity--have we not the right to protect ourselves against the stream which damages our fields, by building dikes and altering its course? The end of endeavor is permanent happiness, and this can be attained through virtue alone. The passions which are useful to society compel the affection and approval of our fellows. In order to interest others in our welfare we must interest ourselves in theirs--nothing is more indispensable to man than man. The clever man acts morally, interest binds us to the good; love for others means love for the means to our own happiness. Virtue is the art of making ourselves happy through the happiness of others. Nature itself chastises immorality, since she makes the intemperate unhappy. Religion has hindered the recognition of these rules, has misunderstood the diseases of the soul, and applied false and ineffective remedies; the renunciation which she requires is opposed to human nature. The true moralist recognizes in medicine the key to the human heart; he will cure the mind through the body, control the passions and hold them in check by other passions instead of by sermons, and will teach men that the surest road to personal ends is to labor for the public good. Illumination is the way to virtue and to happiness.