If mistake is operative at law it prevents the formation of a contract.1

In granting rescission on the ground of mistake, equity proceeds upon the theory that there is a contract, but that equity may give relief against the enforcement of such contract if it would be unequitable to permit its enforcement; and not upon the theory that the parties, by reason of such mistake did not enter into a contract2 The fact that a judgment at law has been rendered between the parties on the theory that a contract is valid, does not prevent relief in equity on the ground of mistake.3 If the instrument is under seal in a jurisdiction in which a seal has its common-law effect, it can not be avoided at law for mistake, but a suit in equity for rescission is necessary.4 valid and voidable. If upon being aware of the alleged fraud they chose to go on, their conduct would justify the defendant's contention that they affirmed the validity of the contract: Plympton v. Dunn, 148 Mass. 523; Ginn v. Almy, 212 Mass. 486, 493. But under the explanatory and charging allegations, that because of their gradual development they did not realize and appreciate the importance and effect of the differences or changes until after the work had been done and the final measurements ascertained, we shall consider the grounds upon which they rely for rescission in the order stated in the bill, even if in view of all the alternative and qualifying allegations it seems doubtful whether actual fraud has been charged"; Winston v. Pittsfleld, 221 Mass. 356, 108 N. E. 1038.

17 Phetteplace v. Bucklin, 18 R. I. 297, 27 Atl. 211.

18 Phetteplace v. Bucklin, 18 R. I. 297, 27 Atl. 211.

19 Williams v. Hamilton, 104 la. 423, 65 Am. St. Rep. 475, 73 N. W. 1029; Althoff v. Torrison, 140 Minn. 8, 167 N. W. 119.

20 Althoff v. Torrison, 140 Minn. 8, 167 N. W. 119.

1 See Sec. 251 et seq.

2 Welch Pub. Co. v, Johnson Realty Co., 78 W. Va. 350, L. R. A. 1917A, 200, 89 S. E. 707.

3 Scott v. Hall, 58 N. J. Eq. 42, 43 Atl. 50.

4 Mdsaac v. McMurray, 77 N. H. 466, L. R. A. 1916B, 769, 93 Atl. 115.