The aim of this chapter is to explore different possible ways of thinking about the connection between the nature of contractual agreements and the rich array of notions that comprise the structure of contract formation. It starts from one axiom regarding the nature of contracts: contractual obligations and rights are necessarily brought about by both parties’ assents (the ‘Necessity of Agreement’ axiom or ‘NOA’). It is maintained that if we adopt NOA, there are at least two different mechanisms by which contracting agents may form a contractual agreement. One is well known to anyone familiar with modern contract law: ‘offer and acceptance’. The other has been interestingly neglected by most contract lawyers and theorists: ‘contractual subscription’. The notion of contractual subscription is developed, and then discussion of the concepts of offer and acceptance. Drawing on Reinach’s idea of a ‘social act’, an account of ‘juridical acts’ is provided. Juridical acts, it is argued, are a type of social act, and contractual offers are a type of juridical act. Finally, the role of another important notion in contract formation is analyzed, that of a ‘promise’. Contrary to several contemporary writers, it is held that the act of making a promise, in its elementary form at least, is neither necessary nor sufficient for the formation of a contract. The chapter concludes by offering a thesis regarding the connection between NOA and morality of contractual enforcement.

Enforceable promises occur when the promisor can no longer revise her promise because a promise is intended to, and has, changed the promisee's decisions.