When an intended legal act is induced by mistake in the sense that it would not have occurred had the actor known the truth, the generally accepted method of analysis in our law is that the act is legally effective; the mistake becomes important only in determining whether it provides a ground for setting aside or rescinding the transaction. If a donor makes a gift while laboring under some fundamental mistake such as the identity of the donee or the donee's relationship to him, the gift is in the first instance effective, but the donor may be able to obtain rescission because of the mistake. Thus a donor obtained rescission of a gift in one case on proof that it was made in the mistaken belief that he and the donee were married when in fact the donee was married to another man. If this had been a testamentary gift, no such relief would have been given. In such a case, the person who would best know whether the donor held the belief in question and whether he would have made the bequest had the truth been known, would be the donor himself, but he is dead. The testimony of others with respect to these facts is apt to be untrustworthy, and this has led the courts to refuse to give effect to such evidence through the use of remedies which are generally available in connection with inter vivos transactions. This general attitude runs through most of the law of wills. It finds expression, for example, in the refusal of equity to reform a ·will for mistake, even though the circumstances are such that reformation would be granted had the gift been made during the donor's lifetime.
George E. Palmer,
Dependent Relative Revocation and Its Relation to Relief for Mistake,
Mich. L. Rev.
Available at: https://repository.law.umich.edu/mlr/vol69/iss6/2