Where damages look at what the claimant has lost, this body of law asks what the defendant has gained and whether it would be unjust to retain it. This chapter begins with the nature of restitution and the four elements of an unjust enrichment claim, then examines what counts as enrichment, the answer of subjective devaluation, and the requirement that the gain came at the claimant's expense. It works through the recognised unjust factors — failure of basis and mistake chief among them — before turning to how restitution is measured and the defences, including change of position, that can defeat a claim. The chapter closes with quantum meruit claims, the entire obligations doctrine and its exceptions for partial performance, and the rules governing deposits, part-payments and the exceptional remedy of an account of profits.
