We have, indeed, insisted that in all moral codes there will be found some form of prohibition of the use of violence, to persons or things, and requirements of truthfulness, fair dealing, and respect for promises. These things, granted only certain very obvious truisms about human nature and the character of the physical world, can be seen in fact to be essential if human beings are to live continuously together in close proximity; and it therefore would be extraordinary if rules providing for them were not everywhere endowed with the moral importance and status which we have described. It seems clear that the sacrifice of personal interest which such rules demand is the price which must be paid in a world such as ours for living with others, and the protection they afford is the minimum which, for beings such as our selves, makes living without others worth while. These simple facts constitute . . . a core of indisputable truth in the doctrines of Natural Law.