What type of contract relies on acts being done in consideration for a promise?

A unilateral contract is defined by the nature of the promise it encompasses; one party makes a promise in exchange for a specific act by another party. In this scenario, the promise becomes enforceable when the act is performed. The classic example is a reward contract, where one person offers a reward for the performance of a particular action, such as returning a lost dog. The offeror is making a promise that is contingent upon the completion of that act.

In contrast, implied contracts rely on actions or circumstances to demonstrate an agreement without explicit verbal or written promises. Express contracts involve clear, articulated agreements, often documented in writing, while joint contracts typically pertain to agreements made between two or more parties who share obligations and rights. Hence, the distinguishing feature of the unilateral contract – that an act triggers a promise – is what makes it the correct choice.