This section is from the book "The Law Of Contracts", by William Herbert Page. Also available from Amazon: Commercial Contracts: A Practical Guide to Deals, Contracts, Agreements and Promises.
Executory contract to convey realty. The effect of failure of title to a part of the realty which the vendor has agreed to convey to the purchaser, upon the remaining covenants of such contract, depends on the question whether the part to which such title fails was a material part of the contract for which the purchaser stipulated, or whether it was a relatively minor and immaterial part of the contract. If the part of the realty to which title fails is a material part of the subject-matter for which the purchaser has stipulated, the purchaser may, if he wishes, treat such failure of title as a discharge of the entire contract.1 If, however, the realty to which title has failed was a minor and immaterial part of the entire transaction, the purchaser can not treat the contract as discharged by reason of such failure of title.2