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500 HARVARD LAW REVIEW. perty of the plaintiff by means of a tort, or upon faith of a consensual right, and the property can be restored.) 2. ht Value. (Possible if the defendant has received a benefit from the plaintiff by means of a tort, or upon faith of a consensual right.) The resemblance between restitution in value, upon the breach of a consensual obligation and the similar restitution upon a tort is purely quantitative. It is so exact, however, in that particu- lar that the two forms of the obligation may be conveniently, though perhaps not very scientifically, treated together. In every case of restitution in value, inspection shows that there are four conditions to be satisfied. In the first place, the plaintiff must have lost something ; in the second place, the defendant must, have gained something ; in the third place, that which the plain- tiff has lost must be identically that which the defendant has gained ; and, in the fourth place, there must have been a breach of right, which may be a breach of a consensual right or a tort. If any of the first three conditions do not obtain, there is nothing to restore, and if the fourth does not obtain, there is no duty, since the plaintiff cannot ask a remedy where there is no wrong. The principle of restitution in value, by reason of its rather un- scientific character, probably cannot be stated in a form that is satisfactorily concise ; but perhaps the following will serve : Upon a tort or upon the breach of a consensual obligation the defendant shall restore the value of whatever the plaintiff has lost and he has gaiiied. This principle of restitution in value, or, more shortly, restitu- tion, I believe to be substantially what is intended by Professor Keener in his doctrine of unjust enrichment. That doctrine, how- ever, has been applied by him to many cases which cannot come under the head of restitution, and it is necessary now to ascertain the differences between the two. In the principle of unjust enrichment, three elements must ob- tain, — expense of the plaintiff, enrichment of the defendant, and, finally, injustice. Now, it is clear that expense of the plaintiff and enrichment of the defendant in the one principle are identical with loss by the plaintiff and gain by the defendant in the other. The condition of restitution, however, that what the plaintiff loses must