The concept of ‘remedy’ used in this chapter encompasses a court order replicating a preexisting right, not a response to civil wrongdoing. Restitutionary remedies responding to unjust enrichment differ from remedies responding to a wrong (breach of contract, tort, or equitable wrong). As noted in Ch 1, they do not fit easily into a division between the primary right and the secondary remedy. It is for this reason that the cause of action and the remedy overlap, and they are notoriously difficult to untangle. Discussions of restitutionary remedies inevitably turn into discussions of the cause of action.

The law of civil remedies has frequently been described as a ‘capstone’ private law subject. In other words, it is the culmination of a student’s knowledge of private law, and it is intended to assist all the disparate strands from previously studied private law subjects to come together.

It is for this reason that we will take a generally ‘functional’ approach to the organisation of this book, grouping remedies from across different areas according to the broad functions they perform so that parallels and contrasts can be made.

Most of the remedies discussed in this book are personal remedies (apart from the proprietary consequences of rescission). Personal remedies, as the name suggests, are directed at the person of the defendant. The defendant must comply with the court order. By contrast, proprietary remedies are directed at property to which the defendant holds title, not to the person.

Proprietary remedies are difficult to allocate on a functional basis. We have not attempted to do so, as the rationales behind the imposition of proprietary remedies vary, and the criteria for their award are uncertain and contested.

It should be noted at the outset that this chapter does not purport to provide an exhaustive account of proprietary remedies. It is presumed that the reader already has a knowledge of trust law and the principles governing the creation of trusts and equitable liens. What follows is an overview from a remedies perspective.

The availability of proprietary remedies in common law is limited. Even where the defendant has committed a proprietary tort, the common law tends to award damages as a remedy. There is no rei vindicatio, or ability of a plaintiff to demand the return of property from a defendant, at common law. Consequently, the proprietary remedies we discuss in this chapter are equitable in origin.

Unjust enrichment is a plausible cause of action for individuals whose data has been collected and used without their consent, to train, develop, or improve AI systems, or which has been sold for such purposes. Disgorgement of profits may be possible in some situations where the defendant has unlawfully collected or used personal data. Gain-based remedies have a number of advantages in this context, including the fact that it may be relatively easy to ascertain the gain, but demonstrating the loss will be considerably harder. However, contractual pre-emption may limit the utility of claims for unjust enrichment.

Modern legal systems generally have a category of obligations known variously as restitution, unjust enrichment, unjustified enrichment or some variant of these. Whichever legal system they are found in, they have a common source in Roman law: the stoic idea that enrichment at the expense of another is unjust, obligations quasi ex contractu and the different forms of non-contractual condictiones. This chapter traces the development of the ideas from Justinian to the modern day, picking up ideas of equity along the way. It focuses on the shifting principles underlying the category, typified by its name, rather than its concrete instantiations, aiming to trace the largely unthinking patterns of borrowing from one legal system to another and from one language to another.

This chapter does not purport to provide an exhaustive account of proprietary remedies. It proves a brief remedial overview of how proprietary remedies work. Because proprietary remedies are enforceable against property rather than a specific person, they are advantageous to plaintiffs in the following ways:

• Proprietary remedies are enforceable against third parties (except bona fide purchasers for value of the legal title without notice).

• Some proprietary remedies (constructive trusts) allow plaintiffs to enjoy appreciations in value of property, or to trace into exchange products

• Specific property may be able to be returned (important if property has special value to the plaintiff)

• Proprietary remedies confer advantages in insolvency by conferring priority to the plaintiff or taking property out of the insolvent estate.

A restitutionary remedy is imposed when a defendant unjustly gains at the plaintiff’s expense (whether money, services, or goods). The defendant must give back what he gained (or the monetary value thereof). This chapter, following the principles text, will deal with personal restitutionary remedies for subtractive unjust enrichment. The history of unjust enrichment is dealt with by the principles text. The law on this topic must be treated with care in an Australian context. (See the excerpt from Roxborough v Rothmans of Pall Mall Australia Ltd in Chapter 1.)

This book chapter advances a hypothesis that judges tend to avoid ex post inefficiency (that is, inefficiency falling to litigants), but judges are less inclined to avoid ex ante inefficiency (that is, inefficiency incurred by future parties). Drawing on three empirical studies which the author has conducted on property cases rendered by courts in Taiwan, this chapter presents preliminary evidence to test this hypothesis. The three studies are consistent with the hypothesis, as judges avoid ex post inefficiency in two studies (co-ownership partition and building encroachment) but fail to avoid ex ante inefficiency in one study (trespass to land).

It is often said, invoking the seventeenth-century Chancellor Lord Nottingham, that the Chancery – or modern courts of equitable jurisdiction – ‘mends no man’s bargain’. This chapter suggests that a legal system which holds that opinion is unwise to do so, that modern courts are not constrained to share that opinion, and that Lord Nottingham himself did not hold it. In various cases, Nottingham granted relief which modified a contractual bargain, or showed himself willing to do so. The power of courts to do so continued to be recognised into the nineteenth century, when it came under fire from the dogma that freedom of contract is sacrosanct. However, modern cases show that the legal system must also advance other values. The necessity to avoid unjust windfalls is an example. The courts can do so, and should be willing to modify contracts in limited situations, without necessarily relying on the language of equity.

What is the nature of a claim to recover restitution as money had and received? Lord Mansfield famously described the claim in terms of equity and conscience, which has led some to maintain that Mansfield fused elements of the common law with elements of equity. This chapter shows that no such thing occurred. Lord Mansfield took the scattered materials of the common law and provided them with a new unifying rationale. That rationale was conscience, but was not a borrowing from the equitable doctrines of the Court of Chancery: he rather developed the common law with concepts also seen in Chancery equity. And while some maintain that Mansfield borrowed from Roman law, that is also shown not to have happened. The upshot is that money had and received – the basic restitutionary remedy – is not a product of the fusion of law and equity, but is an independent development illustrating nothing about fusion.