Perhaps the greater number of primary legal duties, outside the field of contracts, are negative rather than positive, i.e. require one to refrain from acting rather than to act. There are many positive non-contractual obligations, however, and one who confers a benefit in the mistaken belief that he is performing such an obligation, is ordinarily entitled to restitution. It has accordingly been held that a coalmeter of London who mistakenly paid rent to the mayor and subsequently paid it again to the chamberlain, who was entitled to receive it, could recover the money paid to the mayor;1 that one who paid an assessment upon another's property for a street improvement, under the misapprehension that the assessment was upon his own property,2 or who paid an assessment upon his own property under the misapprehension that his vendor had not paid it,3 could recover from the payee the amount paid; that one who mistakenly paid a tax upon property not liable to assessment,1 or an amount in excess of the tax levied upon his property,2 was entitled to restitution; that one who paid a sum of money in compromise of a threatened action to collect a penalty for running a tollgate, in the belief that he was liable to pay the penalty, whereas in fact no such penalty was provided for by law, could recover the money paid.3
1 Bonnel v. Foulke, 1657, 2 Sid. 4. The mistake in this case appears to have been a mistake of law. As to money paid under mistake of law, see ante, Sec. 35 et seq.
2 Mayer v. Mayor, etc., of New York, 1875, 63 N. Y. 455. In this case Andrews, J., said (p. 458): "The circumstances bring the case within the general rule, which authorizes a recovery for money paid by mistake. . . . The city received the money upon a lawful demand, but from a person who was not legally liable to pay it, and we do not find that the circumstance that money paid by mistake is received upon a valid claim in favor of the recipient against a third person prevents a recovery back, provided the claim against the party who ought to pay it is not thereby extinguished or its collection prevented."
3Nevin v. Mankini, 1898, 20 Ky. Law Rep. 224; 45 S. W. 669.