Oliver_wendell_holmes The confusion [between morality and law] with which I am dealing besets confessedly legal conceptions. Take the fundamental question, What constitutes the law? You will find some text writers telling you that it is something different from what is decided by the courts of Massachusetts or England, that it is a system of reason, that it is a deduction from principles of ethics or admitted axioms or what not, which may or may not coincide with the decisions. But if we take the view of our friend the bad man we shall find that he does not care two straws for the axioms or deductions, but that he does want to know what the Massachusetts or English courts are likely to do in fact. I am much of his mind. The prophecies of what the courts will do in fact, and nothing more pretentious, are what I mean by the law.

(Oliver Wendell Holmes, "The Path of the Law," Harvard Law Review 10 [25 March 1897]: 457-78, at 460-1)

Note from KBJ: Replace "law" with "medicine" and "bad man" with "sick man" and you will see how silly Holmes is. "Medicine is but a prophecy of what a doctor will do in fact." Ha! Lawyers such as Richard A. Posner think highly of Holmes; philosophers, to their credit, do not.