pEvery legal system must decide how to distinguish between agreements that are enforceable and those that are not. Formal bargains in the marketplace and casual promises in a social setting mark the two extremes, but many hard cases lie between. When gaps are left in a contract, how should courts fill them What does it mean to say that an agreement is legally enforceable If someone breaks a legally enforceable contract, what consequences followppFor 150 years, legal scholars have debated whether a set of coherent principles provide answers to such basic questions. Oliver Wendell Holmes put forward the affirmative case, arguing that bargained-for consideration, expectation damages, and a handful of related ideas captured the essence of contract law. The work of the next several generations, culminating in Grant Gilmore's iThe Death of Contracti in 1974, took a contrary view. The coherence Holmes had tried to bring to the field was illusory. It was more sensible to see contracts as merel