This section is from the book "The Law Of Contracts", by William Herbert Page. Also available from Amazon: Commercial Contracts: A Practical Guide to Deals, Contracts, Agreements and Promises.
Other reasons may, however, enable the party who has paid money under mistake of law to recover it. Thus where the payment is obtained by B's knowing A's mistake and taking advantage of it ;1 or by actively causing A to make such mistake,2 or by B's using A's mistake as a means of exerting undue influence over A,3 A may recover the money so paid. So where the probate judge rendered services in settling a will contest, contrary to a statute which forbade a probate judge to practice law, payment made to him by his client in ignorance of the law and under his influence may be recovered.4 The principle that a payment made by one person under a mistake of law, and received by one who knows that the other party is paying by reason of such mistake, may be recovered, is not limited to cases of payment to a public officer. Payment under such facts may be recovered from a private person to whom such payment is made.5 In case of a known mistake of law mere silence may be fraud.6
11 Ins. Co. v. Wilkinson, 13 Wall. (U. S.) 222, 233; quoted in McDonald v. Ins. Co., 68 N. H. 4, 6; 73 Am, St. Rep. 548; 38 Atl. 500.
12Ruppell v. Kissel (Ky.), 74 S. W. 220.
1 Toland v. Corey, 6 Utah 392; 24 Pac. 190.
2 Kinney v. Dodge, 101 Ind. 573.
3 Evans v. Funk, 151 111. 650; 38
N. E. 230; Baehr v. Wolf, 59 111. 470.
4 Evans v. Funk, 151 111. 650; 38 N. E. 230.
5 Freeman v. Curtis, 51 Me. 140; 81 Am. Dec. 564; Jordan v. Stevens, 51 Me. 78; 81 Am. Dec. 556.
6 Downing v. Deaborn. 77 Me. 457; 1 Atl. 407.
Under the civil code of California Sec. 1578, payment under a mistake of law, which is shared substantially by all the parties, may be recovered.7 So where the mortgagee's attorney advises the mortgagor that as the mortgage covers the rents and profits, the mortgagee is entitled to the proceeds of the crops, and the mortgagor accordingly pays over the proceeds of the crop, such payment is made under a mistake of law shared by all parties and may be recovered.8