"It is not enough for the knight of romance that you agree that his lady is a very nice girl—if you do not admit that she is the best that God ever made or will make, you must fight. There is in all men a demand for the superlative, so much so that the poor devil who has no other way of reaching it attains it by getting drunk. It seems to me that this demand is at the bottom of the philosopher’s effort to prove that truth is absolute and of the jurist’s search for criteria of universal validity which he collects under the head of natural law...
The jurists who believe in natural law seem to me to be in that naïve state of mind that accepts what has been familiar and accepted by all men everywhere. No doubt it is true that, so far as we can see ahead, some arrangements and the rudiments of familiar institutions seem to be necessary elements in any society that may spring from our own and that would seem to us to be civilized—some form of permanent association between the sexes—some residue of property individually owned—some mode of binding oneself to specified future conduct—at the bottom of all, some protection for the person. But without speculating whether a group is imaginable in which all but the last of these might disappear and the last be subject to qualifications that most of us would abhor, the question remains as to the Ought of natural law.
It is true that beliefs and wishes have a transcendental basis in the sense that their foundation is arbitrary. You cannot help entertaining and feeling them, and there is an end of it. As an arbitrary fact people wish to live, and we say with various degrees of certainty that they can do so only on certain conditions. To do it they must eat and drink. That necessity is absolute. It is a necessity of less degree but practically general that they should live in society. If they live in society, so far as we can see, there are further conditions. Reason working on experience does tell us, no doubt, that if our wish to live continues, we can do it only on those terms. But that seems to me the whole of the matter. I see no a priori duty to live with others and in that way, but simply a statement of what I must do if I wish to remain alive. If I do live with others they tell me that I must do and abstain from doing various things or they will put the screws on to me. I believe that they will, and being of the same mind as to their conduct I not only accept the rules but come in time to accept them with sympathy and emotional affirmation and begin to talk about duties and rights. But for legal purposes a right is only the hypostasis of a prophecy—the imagination of a substance supporting the fact that the public force will be brought to bear upon those who do things said to contravene it—just as we talk of the force of gravitation accounting for the conduct of bodies in space. One phrase adds no more than the other to what we know without it. No doubt behind these legal rights is the fighting will of the subject to maintain them, and the spread of his emotions to the general rules by which they are maintained; but that does not seem to me the same thing as the supposed a priori discernment of a duty or the assertion of a preexisting right. A dog will fight for his bone.
The most fundamental of the supposed preexisting rights—the right to life—is sacrificed without a scruple not only in war, but whenever the interest of society, that is, of the predominant power in the community, is thought to demand it."
--- Natural Law / Oliver Wendell Holmes