This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
If one party to a contract is guilty of a serious breach thereof, the other party may thereupon have the right to treat the contract as terminated. The test is whether the breach goes, as is said, to the essence of the contract. No rule can be laid down as a guide to show what breach does go to the essence. The contract must be construed and the intention of the parties ascertained. It is well to remember, however, this possibility, that very grave deviation by a builder, for instance, from the requirements of a contract, might, at the choice of the owner, discharge the contract. Furthermore, it is to be noted that if in any contract some matter is of especial importance, which in other similar contracts might be of little account, as, for instance, the time of performance, its importance should be made clear. In such case it is desirable to state expressly that the matter in question is of the essence of the contract, although this language in itself would not be held conclusive. If the importance of a certain matter is made clear, then, in case of breach in respect of that matter, the injured person will stand in a better position, and be safe in holding himself discharged from further obligation to proceed under the contract. In case of the termination of a contract, however, the student must remember that if the party terminating it retains the benefit of work already performed by the other party, he will be liable to pay for such work upon an implied contract.