5. Non-contractual promises

Abstract

This chapter considers how promissory and proprietary estoppel intersects with the law of contract. Where an agreement is unenforceable at contract law because some legal prerequisite or formality has not been met, that role is played by the law of estoppel. The law of estoppel works by deeming a party to be legally prevented (‘estopped’) from going back on something she has in the past asserted, promised, or accepted. The effect of estoppel is to hold the person to that past assertion or promise, by preventing her from resiling from it. This chapter first examines the context of promissory estoppel before discussing its requirements and its effect, such as suspending rights and extinguishing debts. It then explains the requirements of proprietary estoppel, namely: there must be a promise or encouragement; the promise or encouragement must induce reasonable reliance; reliance must be detrimental; and unconscionability.