Honor thy father and mother. Thou shalt not murder. Thou shalt not covet thy neighbor’s goods. None of these commandments would make any sense if we had no option. But there is more. When we humans invoke the language of morals—praising and blaming, approving and disapproving, applauding and scorning—we appeal to a shared standard of judgment external to ourselves. Let us call this standard the natural law or the moral law. It differs from the scientific laws of nature in that it tells us not what we do but what we ought to do. Consequently we are free to break these laws in a way that we are not free to violate the laws of gravity.