§ 526. Mistake is of two kinds: mistake in matters of law, and mistake in matters of fact. With regard to the former class, it is a well-established maxim, both in law and equity, that ignorance of law is no excuse for any breach or omission of duty. Ignorantia legis neminem exeusat. The legal presumption is, that every man of reasonable understanding knows the law, when he knows the facts; and this presumption, though arbitrary and false, is founded upon reasons of public policy; for, inasmuch as a thorough knowledge of the principles of law presupposes the studious labor of a life, and the application of that knowledge to many complicated questions of fact can only result in an opinion, in which there is no strict certainty, and from which other equally exercised and accomplished minds may differ,-without some arbitrary rule, imposing upon each man the duty of well considering and understanding the consequences of his own acts and contracts, there would be no limit to the excuse of ignorance, and no security in any agreement. Besides, the opposite rule would encourage ignorance, and rob knowledge and sagacity of its fair fruits; for if a party could claim to set aside his contract on the ground that he was not acquainted with the legal rules governing it, it would be safer to be ignorant than to be wise. The law presumes, therefore, that every man who makes a contract makes it advisedly, and with a knowledge of its legal incidents and consequences; and although this rule, like all arbitrary rules, in some individual cases, works injury and injustice, and cuts the knot which cannot be untied by law, it nevertheless serves to give stability and certainty to the general transactions of commerce, which would otherwise be fluctuating and insecure. Whatever mistakes, therefore, a man may make in the law relating to his contracts, they will be binding, unless fraud or imposition be practised upon him.1 Thus, in Bilbie v. Lumley, 2 East, 471; Brisbane v. Dacres, 5 Taunt. 143; Lowry v. Bourdieu, 2 Doug. 468; Stevens v. Lynch, 12 East, 38; Gomery v. Bond, 3 M. & S. 378; East India Co. v. Tritton, 3 B. & C. 280; Milnes v. Duncan, 6 B. & C. 671; Bramston v. Robins, 4 Bing. 11; Goodman v. Sayers, 2 Jac. & Walk. 263; Mildmay v. Hungerford, 2 Vern. 243; Marshall v. Collett, 1 Younge & Coll. 232. Lord Cottenham, in Stewart v. Stewart, 6 CI. & Fin. 966, has elaborately and critically examined all the cases, and arrived at the same conclusion which was confirmed by the House of Lords. Kelly v. Solari, 9 M. & W. 54, 57, 58.

1 Bissett v. Bissett, 1 Harr. & M'H. 211. In Massachusetts, however, acknowledgment of a deed does not estop the party or his heirs from pleading duress. Worcester v. Eaton, 13 Mass. 371.

2 Bac. Abr. Duress, C.

3 Evans's Pothier on Oblig. pt. 1, art. 3, § 2, p. 15.

1 Doct. and Stud. Dial. 2, ch. 46. This subject has been much discussed and variously decided in the English courts. Lord Mansfield, in Bize v. Dickason, 1 T. R. 285, asserts the rule to have always been, "That if a man has actually paid what the law would not compel him to pay, but what in equity and conscience he ought, he cannot recover it back again in an action for money had and received. But where money is paid under a mistake, which there was no ground to claim in conscience, the party may recover it back again by this kind of action." The doctrine of Lord Mansfield is supported by many authorities; namely, Gibbons v. Caunt, 4 Ves. 849; Stock-ley v. Stockley, 1 Ves. & B. 23; Naylor v. Winch, 1 Sim. & Stu. 555; An-cher v. Bank of England, 2 Doug. 637; Perrott v. Perrott, 14 East, 429; Lansdowne v. Lansdowne, 2 Jac. & Walk. 205; Turner v. Turner, 2 Rep. in Ch. 154. See also an able discussion of this question in the American Jurist, vol. xxiii. p. 371.

The well-established doctrine in England at the present day, is that stated in the text, and most of the cases in which a different doctrine has been declared have been marked by ingredients of fraud and surprise, or have not been purely cases of ignorance of law. The doctrine in the text is declared a promise to pay upon a supposed liability, when there was really no such legal liability, will bind the party so agreeing.

The same rule prevails in the Roman law and in foreign countries on the continent of Europe, where the Roman law prevails. See 3 Burge, Comm, on Col. and For. Law, 742. The question, however, whether money paid under a mistake of law can be recovered, has been much discussed by the civilians. Pothier and Heineccius maintain the negative, and Vinnius and D'Aguesseau the affirmative. Pothier, Oblig. pt. 4, ch. 3, § 1, n. 834; Pothier, Pand. Lib. 22, tit. 6; Comm, ad Leg. vii. do Jur. et Fact. Ignor. Heinec. ad Pand. Lib. 22, tit. 6, § 146; Cujacii Opera, Tom. 4, p. 502, 506, 507; 1 Domat, Civ. Law, B. 1, tit, 18, § 1, n. 13 to 17. Sir W. D. Evans, in his notes to Pothier to Evans's Poth. Oblig. 395), insists that neither a payment nor a promise to pay under a mistake of law, are binding. See Evans's Essay on the Action of Money had and received, ch. 1, § 1. The contrary doctrine is, however, declared in the Roman law. The Digest, Lib. 22, tit. 6, 1. 9, § 3, 5; Code, Lib. 1, tit. 18, 1. 10.

The English and Roman doctrine generally obtains in the United States, and was affirmed by the Supreme Court in the case of Hunt v. Rousmaniere, 1 Peters, 15. This case came up twice before the court; and on the first hearing, the opinion was delivered by Marshall, C. J., in which, after ad-' mitting the general doctrine as stated in the text, he says, "that whatever exceptions there may be to the rule, they will be found few in number, and to have something peculiar in their character." In the subsequent case of Bank of U. S. v. Daniel, 12 Peters, 32, the same principle was adhered to, and the remedial power of a court of equity to relieve against mistakes of law was stated to be a doctrine rather grounded upon exceptions than upon established rules. See also the New York decisions in Shotwell v. Murray, 1 Johns. Ch. 512; Lyon v. Richmond, 2 Johns. Ch. 51; Storrs v. Barker, 6 Johns. Ch. 166; Lyon v. Tallmadge, 14 Johns. 526; Clarke v. Dutcher, 9 Cow. 674; Mowatt v. Wright, 1 Wend. 355. So also in Alabama, Jones v. Watkins, 1 Stew. 81; in Connecticut, Wheaton v. Wheaton, 9 Conn. 96; in New Hampshire, Pinkham v. Gear, 3 N. H. 163; and in Tennessee, Hubbard v. Martin, 8 Yerg. 498. The opposite doctrine obtains in Kentucky. Fitzgerald v. Peck, 4 Litt. 125; Underwood v. Brockman, 4 Dana, 309; and in South Carolina, Lowndes v. Chisolm, 2 M'Cord, Ch. 455; Lawrence v. Beaubien, 2 Bailey, 623; Hopkins v. Mazyck, 1 Hill, Ch. 242. It has been himself to be still liable upon the bill in default of the acceptor, said, three months after it was due, that he knew that he was liable, and if the acceptor did not pay it, he would; it was held, that he was bound by such promise, and that his ignorance of the law was no defence.1 And this rule would specially obtain where a written contract is made, notwithstanding one of the parties misapprehended the law applicable to it.2 So, also, where a party sells an article for which he has given a valuable consideration, fairly believing it to be his own, and it turns out to belong to another, he cannot plead, in defence to an action for the price, that he did not mean to warrant it to be his own; because the law imports a warranty from the fact of his selling it.3 So, also, if a party should give a release of all liability to a principal, he could not afterwards, in an action against the agent, plead that he did not know the rule of law, which renders a release of a principal a release of his agent.4 So, also, where in a contract between the complainant and defendant, the latter agreed to separate iron ore for the former at a specified price per ton, and the complainant, in a bill of equity brought upon the contract, stated that, at the time of making the contract, he was not aware of the existence of the provision in the Revised Statutes, declaring that twenty hunmaking the payment, but it is a premium to the other party for taking advantage of his ignorance. Does not this strike a blow at good morals and fair dealing ? Why, as between the two, should the law by its silence allow him, who has no right or title, to retain that which is the property of another ? Nor is this a case in which there is any difficulty or want of certainty or proof, for, even prima facie, no man pays away money which is not due, except as a gift or loan; and certainly the excuse of ignorance of law in such a case is as complete and satisfactory a reason why the money ought not to be paid as could be wished. See the able essay of D'Aguesseau on Mistakes of Law, and also that of Vinnius on the same subject, translated and appended to 2 Evans's Pothier on Oblig. 409, 437, as well as the essay of Sir W. D. Evans, in the same edition of Pothier, cited above.