The nature of responsibility for gain: Gain, harm and keeping the lid on pandora's box

This chapter examines the nature and origins of legal responsibility for gain in private law. Contrary to recent suggestions, it argues that such responsibility is consistent with our traditional, liberal premises and stems from the relationship between a defendant's gain and some harm to the plaintiff (conceived of as a set-back of her entitlement, not just a factual loss). Legal responsibility for unjust enrichment arises where a defendant has caused harm; where such harm is in prospect and needs to be deterred; or where the plaintiff has suffered harm for which he was not morally responsible. These three different models of responsibility span the line regularly drawn between cases of unjust enrichment 'by subtraction' and 'wrongdoing', raising significant questions about its normative importance. The chapter explains why unjust enrichment law remains an important and necessary private law category, despite its seemingly paradoxical dependence on the concept of harm. It also criticizes the assumption that cases of un-induced mistaken payment are descriptively paradigmatic of unjust enrichment law. Most types of restitutionary liability, it argues, entail the defendant causing harm