The common law of England in 1600 had no concept of restitution (in the current Anglo-American sense) or unjust enrichment. The latter phrase had not yet been imported into the language, while the word ‘restitution’ bore the much narrower meaning of restoring someone to something which had been lost or taken from him. There was a family of restitutionary writs, in that earlier sense, sufficient in number to warrant a heading ‘Restitution’ in the law-books; but the learning there assembled has no bearing on the law of restitution as now understood. The absence of restitutionary terminology in the modern sense was matched by a conceptual void. Someone who intervened in another's affairs to confer an unrequested benefit was as likely to be taken for a wrongdoer as to be thought worthy of reward. On the same principle, the common law seems not to have contemplated the recovery of compensation, outside the law of contract, for improving another's property. Any obligation to render money (other than damages) had to arise from debt, promise or accountability. Of these three notions, the last, derived from the action of account (praecipe quod reddat compotum), is the most easily recognisable as embodying what in modern terms we should regard as a restitutionary principle. The action of account could be used to enforce non-contractual obligations, such as the fiduciary duty arising from a trust of money, or the moral duty to restore money paid by mistake.