Probably no lawyer of the present day will deem it accurate to say that relief can never be given in respect of a law. [Per Sterling, J., in Alcard v. Walker, (1876) 2 Ch. 369, 381]. ‘It is said that 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 in the sense of denoting a private right, that maxim has no application. Private right of ownership is a matter of fact : it may be the result of matter of law : but if the parties contract under a mutual mistake and misapprehension as to their relative and respective rights, the result is that the agreement is liable to be set aside as having proceeded upon a common mistake.’ [Lord Westbury, Cooper v. Phibbs, (1867) 2 H 149, 170; Kuchwar Lime & Stone Co. v. Secy. Of State, 1937 Pat 65, S.B.; see also Ram Chundra v. Ganesh, 21 C.W.N. 404].
‘If a party, acting in ignorance of a plain and settled principle of law, is induced to give up a portion of his indisputable property to another under the name of a compromise, a court of equity will relieve him from the effect of his mistake.’ [Naylor v. Winch, (1824) 1 S. & S. 555].
In a case where the mistake imputable to the party was a matter of law arising out of the doubtful construction of a grant, Lord Chelmsford observed:
“This is very different from the ignorance of a well-known rule of law. And there are many cases to be found in which equity, upon a mere mistake of law, without the admixture of other circumstances, has given relief to a party who has dealt with the property under the influence of such mistake”. [Earl Bauchamp v. Winn, (1873) 6 HL 223, 234].
The true state of law, whether foreign or domestic, is apparently always a fact and the distinction is one of policy rather than of principle. [Jordan v. Stevens, (1863) 51 Me 78]. [Section 22, Contract Act].