As a rule, ignorance or mistake of law, by reason of which the parties do not understand the legal effect of their contract, does not avoid it, unless there is some fraud, or unless there is a relation of confidence between the parties.43
In cases where the nonexistence of a right is concerned, it has been said that the mistake is not a mistake of law, so as to render the avoidance of a contract on that ground a violation of the rule that ignorance of law is no excuse. "It is said, 'Ignorantia juris haud excusat;' but in that maxim the word 'jus' is used in the sense of denoting general law - the ordinary law of the country. But, when the word 'jus' is used as denoting a private right, that maxim has no application. Private right of ownership is a matter of fact; it may be the result also of a matter of law; but, if parties contract under a mutual mistake and misapprehension as to their relative and respective rights, the result is that that agreement is liable to be set aside as having proceeded upon a common mistake."44 Under this rule, the sale of a thing which, unknown to Ignorance of foreign laws, including the laws of a sister state, is regarded as ignorance of fact, and not of law, since a person is not bound to acquaint himself with them.46
42 Greene v. Bateman, 2 Woodb. & M. 350. See, also, Rupley v. Daggett, 74 I11. 331; Rovegno v. Defferari, 40 Cal. 459; Peerless Glass Co. v. Tinware Co., 121 Cal. 641, 54 Pac. 101. See "Sales," Dec. Dig. (Key-No.) § 36; Cent. Dig. §§ 63, 64
43 Birkhauser v. Schmitt, 45 Wis. 316, 30 Am. Rep. 740; Fish v. Cleland, 33 I11. 243; Hunt v. Rhodes, 1 Pet 1, 7 L. Ed. 27; Storrs v. Barker, 6 Johns. Ch. 166, 10 Am. Dec. 316; Starr v. Bennett, 5 Hill (N. Y.) 303; Bank of United States v. Daniel, 12 Pet. 32, 9 L. Ed. 989; Mellish v. Robertson, 25 Vt 603; Good v. Herr, 7 Watts & S. (Pa.) 253, 43 Am. Dec. 236; Rice v. Manufacturing Co., 2 Cush. (Mass.) 80; Dodge v. Insurance Co., 12 Gray (Mass.) 65; Hubbard v. Martin, 8 Terg. (Tenn.) 498; Townsend v. Cowles, 31 Ala. 428; Christy v. Sullivan, 50 Cal. 337; Wheaton v. Wheaton, 9 Conn. 96; Goltra v. Sanasack, 53 I11. 458; Upton v. Tribilcock, 91 U. S. 45, 23 L. Ed. 203; Porter v. Jefferies, 40 S. C. 92, 18 S. E. 229; Osburn v. Throckmorton. 90 Va. 311, 18 S. E. 285; Pittsburgh & L. R. Iron Co. v. Iron Co., 118 Mich. 109, 76 N. W. 395; post, pp. 226, 542. But see Lowndes v. Chisholm, 2 McCord, Eq. (S. C.) 455, 16 Am. Dec. 667. In North Dakota a mistake of law common to both parties renders the contract void by statute. Silander v. Gronna, 15 N. D. 552, 108 N. W. 544, 125 Am. St. Rep. 616. See "Contracts," Dec. Dig. (Key-No.) § 93; Cent. Dig. §§ 415-419.
44 Cooper v. Phibbs, L. R. 2 H. L. 170, per Lord Westbury. And see Wilson v. Insurance Co., 60 Md. 157; Toland v. Corey, 6 Utah, 392, 24 Pac. 190; Lovell v. Wall, 31 Fla. 73, 12 South. 659; Motherway v. Wall, 168 Mass. 333, 47 N. E. 135; Morgan v. Bell, 3 Wash. 554, 28 Pac. 925, 16 L. R. A. 614. "In the often quoted passage * * * he [Lord Westbury] only meant that certhe parties, already belongs to the buyer, or does not belong to the seller, is void.45 This is not a mistake of law, but of fact.
A mistake in drawing up a contract, or a mistake in the legal effect of a description in a deed or other writing, or in the use of technical language, may be ground for relief in equity.47