The plaintiff is entitled to interest from the time when the principal sum recovered by him ought to have been paid, - in other words from the date when the cause of action arose. This has been thought to mean from the time of an election to sue in assumpsit. Said the court in Dougherty v. Chapman:2
"By electing to waive the tort, the plaintiff becomes entitled to the proceeds of the sale, but up to that time he was not entitled to such proceeds. The right to the proceeds accrued by force, and at the moment of election, and not before. As the plaintiff was not entitled to the proceeds of the sale until he made an election, as a matter of course he was not entitled to interest prior thereto."
Here again is the common fallacy that the obligation to make restitution is imposed upon the defendant by the act of the plaintiff in electing to "waive the tort." In the true view of the case, the obligation arises, not from an act of the plaintiff, but by operation of law immediately upon receipt of the benefit by the defendant, and interest is therefore properly recoverable from the date of such receipt.
1 Abbot v. Town of Fremont, 1887, 34 N. H. 432. 21888, 29 Mo. App. 233, 242.
Applying the rule that the plaintiff is entitled to interest from the date when the principal sum ought to have been paid, it is clear that when the judgment is for money received by the defendant, either from the plaintiff or from a third party, interest from the date of the receipt of such money by the defendant should be added;1 that when the judgment is for the value of goods wrongfully taken or detained, interest should run from the date of such wrongful taking or detention; that when the judgment is for the value of the use of the plaintiff's goods or the value of the compulsive service of the plaintiff or his child or apprentice, interest should be allowed from the date of the termination of such use or service, or, perhaps, from the date of the expiration of each week or month (depending upon the unit period for which property of the kind is ordinarily hired or services of the kind ordinarily obtained) of such use or service.