to choose have driven us to seek something better. Obligation, the Roman term, meaning the relation of the parties to what the analytical jurists have called a right _in personam_ is an exotic in our law in that sense. Moreover the relation is not the significant thing for systematic purposes, as is shown by civilian tendencies in the phrases "active obligation" and "passive obligation" to extend the term from the relation to the capacity or claim to exact and duty to answer to the exaction. The phrase "right _in personam_" and its co-phrase "right _in rem_" are so misleading in their implications, as any teacher soon learns, that we may leave them to the textbooks of analytical jurisprudence. In this lecture, I shall use the simple word "liability" for the situation whereby one may exact legally and the other is legally subjected to the exaction. Using the word in that sense, I shall inquire into the philosophical basis of liability and the system of the law on that subject as related to that basis. Yellowplush said of spelling that every gentleman was entitled to his own. We have no authoritative institutional book of Anglo-American law, enacted by sovereign authority, and hence every teacher of law is entitled to his own terminology. So far as the beginnings of law had theories, the first theory of liability was in terms of a duty to buy off the vengeance of him to whom an injury had been done whether by oneself or by something in one's power. The idea is put strikingly in the Anglo-Saxon legal proverb, "Buy spear from side or bear it," that is, buy off the feud or fight it out. One who does an injury or stands between an injured person and his vengeance, by protecting a kinsman, a child or a domestic animal that has wrought an injury, must compound for the injury or bear the vengeance of the injured. As the social interest in peace and order--the general security in its lowest terms--comes to be secured more effectively by regulation and ultimate putting down of the feud as a remedy, payment of composition becomes a duty rather than a privilege, or in the case of injuries by persons or things in one's power a duty alternative to a duty of surrendering the offending child or animal. The next step is to measure the composition not in terms of the vengeance to be bought off but in terms of the injury. A final step is to put it in terms of reparation. These steps are taken haltingly and merge into one another, so that we may hear of a "penalty of reparation." But the result is to turn composition for vengeance into reparation for injury. Thus recovery of a sum of money by way of penalty for a delict is the historical starting point of liability.