A property owner and a landscape architect signed a detailed writing in which the landscape architect agreed to landscape the owner's residential property in accordance with a design prepared by the landscape architect and incorporated in the writing. The owner agreed to pay $10,000 for the work upon its completion. The owner's spouse was not a party to the agreement, and had no ownership interest in the premises. At the owner's insistence, the written owner-architect agreement contained a provision that neither party would be bound unless the owner's law partner, an avid student of landscaping, should approve the landscape architect's design. Before the landscape architect commenced the work, the owner's law partner, in the presence of both the owner and the landscape architect, expressly disapproved the landscaping design. Nevertheless, the owner ordered the landscape architect to proceed with the work, and the landscape architect reluctantly did so. When the landscape architect's performance was 40% complete, the owner repudiated his duty, if any, to pay the contract price or any part thereof.
If the landscape architect now sues the owner for damages for breach of contract, which of the following concepts best supports the landscape architect's claim?