Restitution and unjust enrichment

Restitution and unjust enrichment is the field of law relating to gains-based recovery. In contrast with damages (the law of compensation), restitution is a claim or remedy requiring a defendant to give up benefits wrongfully obtained. Liability for restitution is primarily governed by the "principle of unjust enrichment": A person who has been unjustly enriched at the expense of another is required to make restitution. This principle derives from late Roman law, as stated in the Latin maxim attributed to Sextus Pomponius, Jure naturae aequum est neminem cum alterius detrimentum et injuria fieri locupletiorem ("By natural law it is just that no one should be enriched by another's loss or injury"). In civil law systems, it is also referred to as enrichment without cause or unjustified enrichment. In pre-modern English common law, restitutionary claims were often brought in an action for assumpsit and later in a claim for money had and received. The seminal case giving a general theory for when restitution would be available is Lord Mansfield's decision in Moses v Macferlan (1760), which imported into the common law notions of conscience from English chancery. Blackstone's Commentaries also endorsed this approach, citing Moses. Where an individual is unjustly enriched, modern common law imposes an obligation upon the recipient to make restitution, subject to defences such as change of position and the protection of bona fide purchasers from contrary equitable title. Liability for an unjust enrichment arises irrespective of wrongdoing on the part of the recipient, though it may affect available remedies. And restitution can also be ordered for wrongs (also called "waiver of tort" because election of remedies historically occurred when first filing a suit). This may be treated as a distinct basis for restitution, or it may be treated as a subset of unjust enrichment. Unjust enrichment is not to be confused with illicit enrichment, which is a legal concept referring to the enjoyment of an amount of wealth by a person that is not justified by reference to their lawful income.