Whenever, a freehold is limited to take effect upon a contingency which may happen before the regular expiration of the preceding estate of freehold, it takes effect in defeasance of such interest. The executory limitation thus operating cuts off the prior interest abruptly. By the "intrinsic force" of the executory limitation the preceding estate is terminated. The gift over operates to destroy, to divest,' in defeasance of the prior gift. In the words of LORD LANGDALE, Master of the Rolls, in Jackson v. Noble 2 the preceding estate is "defeated by a contingent executory gift over."
Harold M. Bowman,
How a Conditional Limitation Operates,
Mich. L. Rev.
Available at: https://repository.law.umich.edu/mlr/vol16/iss1/3