2l6 HARVARD LAW REVIEW. the duty is to act are quasi-contracts, in which case quasi-contracts would include many contracts. Both of these results the learned author would be the first to deny. It would seem, however, that in each case he had in mind not one, merely, but two, criteria for determining the character of the obligation under discussion, — that is to say, he had in mind not only the criterion of the presence or absence of assent, but also the criterion of the affirmative or negative character of the obligation, — and that he contented himself with applying that one about which there seemed to him to be the most doubt, and left the reader to apply the other. So considered, his reasoning may in each case be fully stated thus: an element in the obligation of contracts is the assent of the parties ; an ele- ment in the obligation a violation of which constitutes a tort is that the duty is to forbear ; in this obligation under discussion neither of these elements appears; it shall, therefore, be relegated to a third class of obligations to which the name quasi-contracts shall be assigned. This analysis I believe to be a just statement of the author's position. If it is not, I have failed to find the principle upon which he groups such varying obligations under one head. If we assume it to be his true position, it follows that a division of obligations into torts, contracts, and quasi-contracts, is an exhaustive division, that is, it includes under one or the other head all possible obliga- tions. It is valuable also as calling attention to, and successfully combating, the common error that confuses consensual and non- consensual obligations; but it is unscientific, however, as a per- manent scheme of classification, because in the residuary class it neglects the elements both of likeness and of common origin, upon one or the other of which all scientific classification is founded, and upon the second of which the learned author, as we have seen, based his objection to the usual classification. His residuary class is only a conglomerate of unrelated obligations, and is not a true class at all. It is as if the animal kingdom were divided into man, monkeys, and all other animals, — which is division, rather than classification. Another classification, however, may be suggested as that which the learned author had in mind, as follows : Obligations may be divided into those imposed by the will of the parties and those imposed by operation of law, and the latter may be again divided into those of which the obligation is to forbear and those of which the obligation is to act. Set forth diagram- matically, the division is like this:
