When a contract contains within itself express or implied provisions for which it may be terminated under certain circumstances, these are known as conditions subsequent. The forms which such conditions subsequent may take are practically unlimited. The happening or not happening of any conceivable fact may be the basis of a condition subsequent. The most important class of conditions are those where one party is given the option to rescind the contract upon certain conditions, for instance, in contracts of sale, the purchaser is often given the right to return the property upon the breach of a warranty contained in the contract.6

6 Head vs. Tattereall, L. R. 7, Exch. 7, 14; Ray vs. Thompson, 12 Cush. (Mass.), 281.