In the swing set case, the woodworker's performance illustrates acceptance of which type of contract?

• A. Acceptance by performance under a unilateral contract
• B. Counteroffer
• C. Mutual mistake
• D. Illusory promise

Answer: (A)

The main idea here is acceptance by performance in a unilateral contract. In a unilateral contract, the offeror promises to pay in exchange for the offeree completing the specified performance. The woodworker’s act of building the swing set is exactly that kind of performance—accepting the offer not by promising to perform, but by actually performing. Once the woodworker begins and completes the work, the contract is formed, and the offeror is obligated to pay upon completion.

This isn’t a counteroffer, because there’s no rejection or alteration of terms being proposed; it’s simply the offeree fulfilling the requested task. It isn’t mutual mistake, since there isn’t a shared erroneous belief about a material fact. It isn’t an illusory promise, because the offeror has made a definite promise to pay upon the completion of the performance, which becomes binding once the performance occurs.