The waiver set up is not of a condition precedent, or of the time, place, or manner of the performance of a con-, tract; if it can be called a waiver at all, it is a waiver of the right to require a conveyance of all the land which the defendant by the bond was bound to convey. If the plaintiff had *374accepted the deed tendered, it would have been a question for the jury whether she thereby waived a claim for damages occasioned by the failure of the defendant to convey all of the land described in the bond, and the knowledge or ignorance of the plaintiff, when she accepted the deed, of the defect in the description of the land, would be material upon the question of waiver. There are indeed acts to which the law affixes a specific effect independently of the intention of the parties, but the acts of the parties in this case are not of that character. Fox v. Harding, 7 Cush. 516. Moulton v. McOwen, 103 Mass. 587. Taylor v. Cole, 111 Mass. 363. Palmer v. Sawyer, 114 Mass. 1. The plaintiff did not accept the deed, and the defence is, that, although the defendant did not offer to perform her contract according to its terms, yet the plaintiff waived the defect in the offer which was made. As the defect relates to the quantity of land to be conveyed, the defence is in effect that the plaintiff agreed to accept a substituted performance for that which the contract required, and that the defendant offered to perform the contract according to the new agreement; or, if put on.the ground of waiver, that the plaintiff intentionally relinquished to the defendant the right to require a conveyance of the land to the centre line of Field Street.
It may be assumed that in this Commonwealth, in an action upon a contract under seal which is executory upon both sides, the defendant may show in defence, that, before any part of the contract has been executed, and before a breach, the parties have agreed to vary its terms, and that-the defendant offered to perform the contract as thus varied. Rogers v. Rogers, 139 Mass. 440. But whether the defence is put upon the ground of waiver or of a new agreement, it is necessary to show-an assent to the change on the part of the plaintiff.
In Darnley v. London, Chatham, & Dover Railway, L. R. 2 H. L. 43, it is said by Lord Chelmsford, on p. 57, “ A waiver must be an intentional act with knowledge; ” and by Lord Cranworth, on p. 60, “ When parties, who have bound themselves by a written agreement, depart from what has been so agreed on in writing, and adopt some other line of conduct, it is incumbent on the party insisting on, and endeavoring to enforce, a substituted verbal agreement, to .show, not merely what he understood to *375be the new terms on which the parties were proceeding, but also that the other party had the same understanding — that both parties were proceeding on a new agreement, the terms of which they both understood.”
In such a case as the present, knowledge on the part of the plaintiff of the form in which the deed and bond were written, if she was ignorant of the legal effect of the language, would not be conclusive against her right of action, even if she had been willing to accept the deed tendered, and had so declared, but for an objection which should be held to be groundless. A mistake in the legal effect of the words in a deed, if it were mutual, or if the words were used by accident or by fraud on the part of the defendant, would be corrected in equity. Canedy v. Marcy, 13 Gray, 373, 377. Stockbridge Iron Co. v. Hudson Iron Co. 107 Mass. 290, 319. See Watson v. Watson, 128 Mass. 152.
In Dresel v. Jordan, 104 Mass. 407, which was a bill in equity for specific performance of an agreement to buy a parcel of land, the defendant agreed to assume a certain mortgage then existing upon the land. The deed tendered contained a condition that this mortgage should be paid by the grantee. The difference in legal effect between a grant upon such a condition and a grant subject to a mortgage which the grantee assumed, was well known to the defendant’s attorneys, and the objection to the deeds on this ground had been considered by them, and was held to have been in fact waived.
In Gerrish v. Norris, 9 Cush. 167, the justice who presided at the trial did not rule that the defendant, “ by not taking the objection to the deed at the time it was tendered which he now raises,” waived- the objection, but submitted the question of waiver to the jury. The statement in the first paragraph of the opinion, however, is too broad if applied to substantial changes in contracts, and seems to have misled the presiding justice in the case at bar.
It does not appear in the present case that the defect in the deed was noticed by the plaintiff, or that the effect of the language used was discussed or considered by the parties; the dispute was wholly upon another matter, and the instructions of the court were in effect, that, if the plaintiff was willing to *376accept the deed if the word “ contemplated ” was stricken out, she waived the substantial mistake in the boundary of the land, whether she knew of it or not. We think that this ruling is erroneous. The jury could not properly find that the plaintiff waived this defect in the deed, unless they found she knew of it, and assented to the change in the boundary. Such assent need not be expressed in terms, but it must be found to have existed as a fact. No question of estoppel, as distinguished from waiver, arises in these exceptions, and we are not called upon to decide whether, if the defendant intended to deliver a deed in conformity with the bond, and the mistake was not pointed out or known to her until the trial, she might not then have tendered a sufficient deed, and, under an amendment of her pleadings, have proved these facts in mitigation of damages.
For the reasons given, a majority of the court are of opinion that the
Exceptions must he sustained.