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.
The building contract, commonly made between the owner and builder, confers certain powers upon the architect. "While the latter is not a party to this contract, and so cannot enforce it, he is by reason of it drawn into the contractual relations of others. For this reason alone, the branch of the law dealing with contracts is an important one to him. Moreover the architect may have occasion to supervise or assist in the making of contracts in behalf of the owner; while in the important matter of right to compensation, the architect is dependent upon the law on this subject.
When competent persons make a contract their rights are fixed thereby. If, however, without any express contract, one person gives services or goods which another person accepts, and if there is no understanding that the transaction is a gift, the person giving the services or goods is not without a right to compensation. The law imposes an obligation upon the person receiving the benefit to make compensation to the person from whom he receives it. This obligation is sometimes called an implied contract, as if, in accepting the benefit, it is impliedly agreed to make recompense. This principle is of great importance and frequent application. It will be seen later that it is applied not only when there is no express contract, but also in some cases where an existing express contract for some reason cannot be enforced.
The principle above stated, that a contract once made by competent parties fixes their rights, is fundamental. Suppose A sues B upon an implied contract for material furnished, claiming $100 as the value thereof. If B alleges and proves that he had a contract with A covering everything for which B seeks to recover, and that A has not complied with the terms of this contract, this will be a defense; unless indeed it can be shown that, in spite of A's failure exactly to fulfil the contract, B has accepted the material. In that case the facts might raise a new implied promise. But if B refused the material, of course no such promise could be implied. On the other hand if A offered material in compliance with the contract, and B refused to receive it, A could hold B answerable for breach of the express contract although B received no benefit therefrom.