Take again a notion which as popularly understood is the widest conception which the law contains—­the notion of legal duty, to which already I have referred.  We fill the word with all the content which we draw from morals.  But what does it mean to a bad man?  Mainly, and in the first place, a prophecy that if he does certain things he will be subjected to disagreeable consequences by way of imprisonment or compulsory payment of money.  But from his point of view, what is the difference between being fined and taxed a certain sum for doing a certain thing?  That his point of view is the test of legal principles is proven by the many discussions which have arisen in the courts on the very question whether a given statutory liability is a penalty or a tax.  On the answer to this question depends the decision whether conduct is legally wrong or right, and also whether a man is under compulsion or free.  Leaving the criminal law on one side, what is the difference between the liability under the mill acts or statutes authorizing a taking by eminent domain and the liability for what we call a wrongful conversion of property where restoration is out of the question.  In both cases the party taking another man’s property has to pay its fair value as assessed by a jury, and no more.  What significance is there in calling one taking right and another wrong from the point of view of the law?  It does not matter, so far as the given consequence, the compulsory payment, is concerned, whether the act to which it is attached is described in terms of praise or in terms of blame, or whether the law purports to prohibit it or to allow it.  If it matters at all, still speaking from the bad man’s point of view, it must be because in one case and not in the other some further disadvantages, or at least some further consequences, are attached to the act by law.  The only other disadvantages thus attached to it which I ever have been able to think of are to be found in two somewhat insignificant legal doctrines, both of which might be abolished without much disturbance.  One is, that a contract to do a prohibited act is unlawful, and the other, that, if one of two or more joint wrongdoers has to pay all the damages, he cannot recover contribution from his fellows.  And that I believe is all.  You see how the vague circumference of the notion of duty shrinks and at the same time grows more precise when we wash it with cynical acid and expel everything except the object of our study, the operations of the law.

Nowhere is the confusion between legal and moral ideas more manifest than in the law of contract.  Among other things, here again the so-called primary rights and duties are invested with a mystic significance beyond what can be assigned and explained.  The duty to keep a contract at common law means a prediction that you must pay damages if you do not keep it—­and nothing else.  If you commit a tort, you are liable to pay a compensatory sum.  If you commit a contract,