rei interventus

rei interventus

in Scots law, a doctrine of PERSONAL BAR that prevents a person who does not want to adhere to a formally defective agreement being allowed to do so by the party who wants the bargain to succeed. There must be important actings by the party wanting to rely on the agreement, known to and permitted by the other party. It prevents LOCUS POENITENTIAE, which is said to exist between informal agreement and formal execution. Its practical importance has been eclipsed by the regime provided by the REQUIREMENTS OF WRITING (Scotland) Act 1995, which provides an equivalent protection for parties affected by a lack of required writing.
Collins Dictionary of Law © W.J. Stewart, 2006

REI INTERVENTUS. When a party is imperfectly bound in an obligation, he may in general, annul such imperfect obligation; but when he has permitted the opposite party to act as if his obligation or agreement were complete, such things have intervened as to deprive him of the right to rescind such obligation; these circumstances are the rei interventus. Bell's Com. 328, 329, 5th ed.; Burt. Man. P. R. 128.

A Law Dictionary, Adapted to the Constitution and Laws of the United States. By John Bouvier. Published 1856.