The invention and spread of contraceptives is the proximate cause of our changing morals. The old moral code restricted sexual experience to marriage, because copulation could not be effectively separated from parentage, and parentage could be made responsible only through marriage. But today the dissociation of sex from reproduction has created a situation unforeseen by our fathers. All the relations of men and women are being changed by this one factor; and the moral code of the future will have to take account of these new facilities which invention has placed at the service of ancient desires.

Our Changing Morals, in The Mansions of Philosophy: A Survey of Human Life and Destiny, (1929), Simon and Schuster, New York, ch. 5. p. 119.