Unjust Enrichment.

Unjust enrichment is one of the three primary sources of civil obligation in private law, standing alongside contract and tort as an independent basis for liability. As Lord Wright recognized in Fibrosa Spolka Akcyjna v. Fairbairn Lawson Combe Barbour Ltd., "any civilised system of law is bound to provide remedies for cases of what has been called unjust enrichment ... generically different from remedies in contract or in tort, and now recognised to fall within a third category of the common law."

The animating principle of unjust enrichment is the reversal of unjustified transfers. Where one party has been enriched at another's expense and no valid legal reason exists to justify that enrichment, the law requires the enriched party to make restitution. Unlike breach of contract or negligence, unjust enrichment does not require proof of any agreement or any wrongdoing. It is a form of true strict liability: liability is imposed simply because a transfer occurred in the absence of juristic reason.

Despite its conceptual simplicity, unjust enrichment is often misunderstood. The word "unjust" misleads many into thinking the subject is a matter of moral intuition or open-ended equity. It is neither. Unjust enrichment is governed by specific rules and a structured analytical framework. As McLachlin J. cautioned in Peter v. Beblow, courts must resist "the tendency to view the action for unjust enrichment as a device for doing whatever may seem fair between the parties."

It is equally important to distinguish unjust enrichment from disgorgement, a remedy available for certain civil wrongs that strips away profits gained through wrongdoing. Restitution reverses a transfer between the parties; the defendant gives back what was received from the plaintiff. Disgorgement strips away gains obtained through wrongdoing, even if those gains came from a third party. The two concepts use the same language but serve fundamentally different functions, a distinction authoritatively clarified by the Supreme Court of Canada in Atlantic Lottery Corp. v. Babstock.

The modern law of unjust enrichment has deep common law roots, though those roots were long obscured by confusing historical labels. Before the abolition of the ancient writ system, claims now understood as unjust enrichment were brought under the writ of indebitatus assumpsit ("being indebted, he promised to pay"). This writ accommodated a variety of claims through what were called the "common counts," including money had and received, money paid for the defendant's use, and quantum meruit (as much as he deserved).

The Quasi-Contract Error

In the late 18th century, Lord Mansfield attempted to systematize these claims in Moses v. Macferlan, drawing on Roman law to explain that certain obligations arose not from genuine promises but were "imposed by law," what the Romans called quasi ex contractu. Over time, the phrase contracted to "quasi-contract," and that unfortunate label caused later generations to view this body of law as merely an appendage of contract, rather than a distinct and independent category. This led courts astray for over a century.

The error was compounded by the widespread misreading of Lord Mansfield's references to "equity" in Moses v. Macferlan. When he described the action for money had and received as a "kind of equitable action," he was invoking the Roman concept of aequitas (reasoned fairness), not the institutional jurisdiction of the Court of Chancery. Despite this, Canadian courts developed the persistent and incorrect belief that unjust enrichment is an equitable doctrine. That error has real and costly consequences.

Unjust Enrichment Is Not Equitable in Origin

The overwhelming majority of restitutionary claims, for mistaken payments, compelled transfers, and services rendered under invalid contracts, developed not in Equity but in Law, through the common law courts and the writ of indebitatus assumpsit. As Pollock C.B. observed in 1849, money had and received "was a perfectly legal action, and no good can result from calling it an equitable one." Lord Sumner similarly confirmed that it "was not devised by the Court of Chancery, nor was it applied there either in form or in substance."

Those errors persist in Canadian jurisprudence and require vigilant correction. They matter in practice because they determine whether courts view restitution as principled liability to be applied by established rules or as open-ended discretion to be invoked where fairness seems to require it.

The Supreme Court's Contribution

Canada led the Commonwealth in recognizing unjust enrichment as an independent principle. The Supreme Court of Canada first acknowledged the principle in Deglman v. Brunet Estate, and then formulated it as a three-part cause of action in Pettkus v. Becker. The law changed again fundamentally in 2004 when Garland v. Consumers' Gas Co. replaced the common law's traditional "unjust factors" model with a civilian-inspired test of "absence of juristic reason." Most recently, Atlantic Lottery Corp. v. Babstock authoritatively separated unjust enrichment from disgorgement of wrongful gains, eliminating decades of terminological confusion.

Every claim for unjust enrichment in Canada must satisfy three elements, regardless of the context in which it arises. Whether the dispute involves a failed contract, a domestic relationship, a commercial fraud, or a mistaken payment, the analytical framework is the same. As Cromwell J. confirmed in Kerr v. Baranow, the "underlying legal principles of the law of unjust enrichment remain constant across subject areas."

1. Enrichment. The defendant received a tangible, monetarily expressible benefit from or through the plaintiff.
2. Corresponding deprivation. The plaintiff suffered a corresponding loss that is the obverse of the defendant's gain, two sides of the same coin.
3. Absence of juristic reason. No valid legal basis, no contract, disposition of law, donative intent, or other legal obligation, justified the transfer.

If all three elements are established, a prima facie right to restitution arises. The defendant may then rely on defences to reduce or extinguish liability. The measure of restitution is capped by the lesser of the defendant's enrichment and the plaintiff's deprivation. Restitution restores the status quo ante. It does not create a windfall for either party.

This unified framework subsumes all the traditional historical heads of recovery: money had and received, quantum meruit, quantum valebant, money paid. Those historical categories remain useful as illustrations of how the principle applies in particular factual contexts, but they no longer operate as independent causes of action alongside unjust enrichment. As McLachlin J. stated in Peel (Regional Municipality) v. Canada, the modern cause of action has "grown out of the traditional categories of recovery" and is "informed by them," but is also "capable of going beyond them."

The first element requires proof that the defendant received a "tangible benefit," something with monetary value. The law applies a straightforward economic approach: money, land, goods, and services all qualify. The purpose of requiring proof of an objective benefit is twofold. First, there must be something capable of monetary quantification in order to calculate the restitutionary award. Second, because unjust enrichment involves true strict liability, the defendant's enrichment places a ceiling on liability. Restitution cannot hurt the defendant relative to the status quo ante.

Subjective Devaluation: The Right of Autonomy

The receipt of an objective benefit does not automatically establish an enrichment for restitutionary purposes. The defendant enjoys what Peter Birks termed a right of "subjective devaluation," the right to assert that liability would intolerably override personal autonomy. The doctrine operates not by allowing the defendant to say that the benefit holds no value at all, but rather by allowing the defendant to say that the benefit was not a spending priority, that the choice to receive it was not freely made.

The recipient's inability to return services does not automatically mean the law should compel payment for them. The doctrine of subjective devaluation operates to protect defendants who never exercised a genuine choice to bear financial responsibility for the benefit conferred.

Overcoming Subjective Devaluation

The plaintiff must overcome the defendant's right of subjective devaluation in one of two ways: by demonstrating either that the defendant exercised a choice to bear financial responsibility, or that the defendant received an incontrovertible benefit.

Request. A request typically reveals both a desire to receive and a willingness to pay. Where the defendant asked for the benefit, there is no valid argument from autonomy. A choice was made. Courts must be careful, however, where requests are made in the expectation that no payment would be required (as sometimes occurs between family members or in quasi-gratuitous commercial arrangements). In such cases, the request does not displace subjective devaluation.

Free acceptance. The defendant may also be held to have chosen responsibility by passively accepting a benefit despite knowing, actually knowing, not merely ought to have known, that the plaintiff expected payment. As the Supreme Court of Canada confirmed in Pettkus v. Becker, free acceptance requires that the defendant "knew or ought to have known" of the plaintiff's expectation.

Retention of a readily returnable benefit. A defendant who retains goods that could easily be returned to the plaintiff has exercised a choice. This principle, recognized in Sumpter v. Hedges and more recently articulated in Cressman v. Coys of Kensington, holds that an enrichment is established where the defendant chooses to keep a benefit that is "readily returnable without substantial difficulty or detriment."

Incontrovertible Benefits

Some benefits are, by their nature, immune to subjective devaluation. An incontrovertible benefit is one that is "demonstrably apparent and not subject to debate or conjecture," as McLachlin J. stated in Peel v. Canada. Three categories are established:

• Money. Money has "the peculiar character of a universal medium of exchange. By its receipt, the recipient inevitably is benefitted." A defendant holding cash cannot argue it is not an economic priority.
• Saving of a necessary expense. Being relieved of an obligation that must be satisfied (a statutory debt, a tax arrears, an unavoidable maintenance cost) is functionally equivalent to receiving money. The defendant can satisfy the restitutionary award with the funds that otherwise would have discharged the necessity.
• Realizable financial gain. Where the plaintiff's contribution has increased the market value of the defendant's asset, and the defendant has realized (or can readily realize) that gain by sale, the enrichment is incontrovertible. Canadian courts have taken a notably broad approach, regularly recognizing enrichments on the basis of realizable gains regardless of the nature of the improved asset, including land and real property.

It bears emphasis that enrichment is assessed objectively, not on a net-benefits basis. In cases involving mutual exchanges, most commonly in domestic relationships, courts must not "short-circuit the proper unjust enrichment analysis" by roughly offsetting what was given and received. As confirmed in Kerr v. Baranow, mutual benefits become relevant only at the stages of juristic reasons, defences, and remedies.

The second element of unjust enrichment serves two functions: it identifies the party with standing to claim restitution, and it combines with the enrichment to quantify the amount of the award. Under the "straightforward economic approach" that governs unjust enrichment, once an enrichment is established, a corresponding deprivation is often not in dispute. The enrichment and the deprivation are simply two sides of the same transfer.

Canada's distinctive formulation of this element, "corresponding deprivation" rather than "at the plaintiff's expense," is not merely semantic. It correctly identifies that unjust enrichment requires a correspondence between the defendant's gain and the plaintiff's loss. They must be obverse manifestations of the same event. This is precisely what distinguishes restitution (which reverses a transfer between the parties) from disgorgement (which strips away gains obtained from third parties through wrongdoing).

What the Deprivation Consists Of

The plaintiff's deprivation is the benefit conferred on the defendant, not the broader economic consequences of having done so. This is a common source of error. In a claim arising from domestic services, for example, the relevant deprivation is the services themselves, not the plaintiff's "sacrificed opportunity to travel" or to "reside near a gentleman friend." Such opportunity costs are irrelevant to unjust enrichment, though they might be relevant to a compensatory claim for breach of contract. Similarly, the law does not additionally require the plaintiff to prove that performing the service caused an economic loss beyond the service itself. As Deglman v. Brunet Estate illustrates, the nephew who performed domestic services for his elderly aunt was entitled to restitution without having to prove that he gave up paid employment to do so.

Indirect Enrichments: Leapfrogging

Canadian law takes a notably permissive approach to indirect enrichments. Unlike English law, which generally requires a direct transactional connection between the parties, Canadian courts recognize that "the corresponding deprivation element does not require that the disputed benefit be conferred directly by the plaintiff on the defendant," as Côté J. confirmed in Moore v. Sweet. Restitution may lie against a remote or indirect recipient, subject always to the three-part analysis and applicable defences. This is consistent with the remedial objective of restitution law, which, as Rothstein J. observed in Pro-Sys Consultants Ltd. v. Microsoft Corp., "allows for recovery by the parties who have actually suffered the harm rather than merely reserving these actions for direct enrichments."

The Sub-Contract Limitation

A critical limitation on indirect enrichment claims arises in sub-contract situations. Where a plaintiff performs work for a general contractor who in turn owes obligations to a defendant property owner, the plaintiff generally cannot claim unjust enrichment directly from the owner. The explanation is not that there is no direct relationship, but rather that the general contract and the sub-contract together constitute juristic reasons that preclude relief. By accepting the sub-contract, the plaintiff accepted the risk that the general contractor might become insolvent. Restitution against the owner would subvert the risk allocation contained in those freely negotiated agreements.

Quantification

Canadian law departs from the Anglo-Australian approach in quantifying restitution. While English and Australian courts calculate restitution exclusively by reference to the defendant's enrichment, Canadian courts cap the award at the lesser of the defendant's enrichment and the plaintiff's deprivation. As confirmed in Atlantic Lottery Corp. v. Babstock and Air Canada v. British Columbia, restitution "simultaneously causes the defendant to give back, and the plaintiff to get back" the unjustified enrichment. It neither advantages the defendant nor confers a windfall on the plaintiff.

The third element of unjust enrichment asks whether the transfer was legally justified. This is the element that determines when an enrichment should be reversed, and it does the most work in distinguishing valid transfers (gifts, contractual payments, lawfully imposed obligations) from unjustified ones (mistaken payments, transfers under invalid agreements, compelled payments).

Under the common law model, the plaintiff had to prove a positive reason to reverse the transfer, such as mistake, compulsion, or failure of consideration. Under the civilian model adopted in Canada, restitution is available unless the defendant can point to a reason that the enrichment should be retained. The shift does not eliminate the historical categories; it relocates them within a restructured test.

In Garland v. Consumers' Gas Co., Iacobucci J. implemented what is now the authoritative Canadian test for restitutionary injustice. The analysis unfolds in two stages.

Stage One: The Established Categories

The plaintiff must negate the four established categories of juristic reason. If the plaintiff successfully negates all four, a prima facie right to restitution arises:

• Contract. "Contract trumps unjust enrichment." Where a transfer occurs in fulfilment of a contractual obligation, unjust enrichment has no role to play to the extent that the event was the subject of a contractually allocated risk. The existence of a contract does not automatically preclude restitution, but it strongly militates against it.
• Disposition of law. A transfer is justified if it occurs in compliance with a valid legal demand, for example, a tax obligation, court order, or regulatory requirement. Where the underlying legal authority is itself invalid (for example, a tax demand that violates the Criminal Code), the juristic reason falls away.
• Donative intent. A gift freely and intentionally made cannot be reclaimed. As long as the plaintiff's donative intention was not vitiated by mistake, undue influence, or other invalidating factor, the defendant is entitled to retain the enrichment. Donative intent extends beyond birthday presents. It applies in commercial contexts where a benefit is deliberately conferred without expectation of return.
• Other valid obligations. A catch-all category encompassing other valid common law, equitable, or statutory obligations that render a transfer irreversible. The essential question is whether some legal obligation, beyond contract, disposition of law, or donative intent, explains and justifies the transfer.

Stage Two: Residual Juristic Reasons

Even if the plaintiff negates all established categories, the defendant may rebut the prima facie claim by demonstrating some "residual" category of juristic reason. Iacobucci J. identified two factors of particular relevance at this stage: the reasonable expectations of the parties and public policy considerations.

This second stage requires careful application. Courts must not use "reasonable expectations" or "public policy" as a vehicle for the kind of palm-tree justice that the structured framework is designed to avoid. As commentators have noted, "reasonable expectations" floating free of any specific legal doctrine do not explain why a defendant should be entitled to retain an unjustified enrichment. The stage-two inquiry is properly directed at identifying specific reasons for retention, not a generalized judicial assessment of fairness.

The Pyramid of Reconciliation

The shift from unjust factors to juristic reasons did not render the historical common law cases irrelevant. As Peter Birks explained, unjust factors and juristic reasons stand in a "pyramid of reconciliation." The historical doctrines (mistake, incapacity, qualified intention, induced intention) did not disappear. They were reinterpreted. Under the Garland framework, they now serve as grounds for negating an ostensible juristic reason rather than as independent reasons to reverse.

For example: a payment made under a mistaken belief that a debt was owed ostensibly looks like a contractual payment (a juristic reason). But mistake vitiates the plaintiff's donative intention and defeats the apparent juristic reason. The historical unjust factor of "mistake" now operates at the level of negating the apparent juristic reason. It reveals that, despite outward appearances, no valid juristic reason actually supported the transfer.

Where unjust enrichment is established and no defence succeeds, the plaintiff is entitled to restitution. Restitution simultaneously restores the plaintiff and the defendant to the positions they occupied before the unjustified transfer. It is inherently backward-looking. It restores the status quo ante. It does not redistribute wealth or fulfill expectations.

Personal & Proprietary Restitution

The primary remedy for unjust enrichment is a personal monetary award, a judgment requiring the defendant to pay the plaintiff a sum equal to (the lesser of) the defendant's enrichment and the plaintiff's deprivation. This is the ordinary remedy in cases involving mistaken payments, services rendered without juristic reason, and benefits conferred in the context of failed or invalid agreements.

The quantum of a personal restitutionary award is calculated objectively. The enrichment is assessed at its market value, subject to any applicable subjective devaluation (where the defendant's request established a discounted expectation of cost) or the change of position defence (where the defendant was disenriched after receipt). Quantum meruit and quantum valebant, terms inherited from the common count system, describe the method of valuing services and goods respectively.

In appropriate cases, restitution may be awarded on a proprietary basis. The most significant proprietary remedy in Canadian unjust enrichment law is the constructive trust. A constructive trust operates by declaring that the defendant holds identified property on trust for the plaintiff. It is not merely a personal right to payment but a real property interest. The plaintiff obtains a share of the property itself.

Proprietary restitution is particularly significant in three situations:

• Insolvency. A proprietary remedy is more valuable than a personal one where the defendant may be insolvent, as it removes the plaintiff from the queue of unsecured creditors.
• Appreciation. Where the relevant property has increased in value since the transfer, a constructive trust allows the plaintiff to share in that appreciation rather than merely recovering the original transfer value.
• Tracing. A proprietary remedy allows the plaintiff to follow and recover assets that the defendant has acquired using the plaintiff's money or property.

The Supreme Court clarified in Kerr v. Baranow that a constructive trust is not available as a matter of course. It requires a connection between the plaintiff's contribution and the specific property over which the trust is sought, and it is available only where a personal award would be "inadequate."

Equitable Accounting and Disgorgement

Distinct from restitution, an accounting of profits (now properly termed disgorgement) may be available where the defendant committed a civil wrong (breach of fiduciary duty, breach of confidence, or certain proprietary torts) and profited as a result. The profit stripped away by disgorgement need not correspond to the plaintiff's loss. The defendant gives up everything gained through the wrong. As confirmed in Atlantic Lottery Corp. v. Babstock, disgorgement is not a remedy for unjust enrichment. It is a remedy for wrongdoing. Mistaking the two causes analytical confusion about what the plaintiff can recover and against whom.

Even where unjust enrichment is fully established, the defendant may reduce or extinguish liability by proving one of several defences. Some are specific to the law of unjust enrichment; others are generally available in private law.

Change of Position

The most important restitutionary defence is change of position. Consistent with the principles underlying the enrichment element, this defence reduces recovery to the extent that the defendant was disenriched after receipt, acting in good faith in the honest belief that the enrichment could legitimately be retained.

The defence reflects a principled balance between the plaintiff's right to restitution and the defendant's right to autonomy. A defendant who spends an unexpected windfall on ordinary household expenses cannot use change of position to escape liability: those expenses would have been incurred in any event. But a defendant who, upon receipt of the windfall, takes a "dream vacation" that would otherwise have been financially impossible can rely on that expenditure to reduce the restitutionary award. The vacation was undertaken in good faith in reliance on the apparent right to retain the enrichment; requiring repayment of that amount would leave the defendant worse off than before the enrichment was received.

Bona Fide Purchase for Value

A defendant who provides value to a transferor in good faith and without notice of any claim affecting the transferred asset is protected from a subsequent restitutionary claim by the plaintiff. This defence is particularly important in three-party situations where property has passed through an intermediate transferor before reaching the defendant.

Limitations, Officiousness & Illegality

Limitation periods. Restitutionary claims are subject to applicable limitation periods. In Ontario, the Limitations Act, 2002 generally imposes a two-year limitation period running from the date the claim was discovered, subject to the ultimate 15-year cap. A cause of action in unjust enrichment normally crystallizes when, in the absence of juristic reason, the enrichment is received by the defendant.

Officiousness. Restitution will be denied where the plaintiff conferred the enrichment officiously, that is, where the plaintiff knowingly intervened to confer a benefit despite the known absence of any request or legal obligation to do so. This defence prevents parties from imposing unrequested benefits on others and then demanding payment. It requires that a plaintiff seeking restitution have had some legitimate interest in making the transfer, whether legal, moral, or practical.

Illegality. A claim for unjust enrichment may be defeated, partially or entirely, where it arises from an illegal transaction and allowing recovery would undermine the policy of the law in prohibiting that transaction. The illegality defence has been significantly constrained in recent years, with courts increasingly applying a principled, proportionate approach. Denial of restitution is not automatic merely because the transaction had an illegal character.

The principle of unjust enrichment applies across a wide range of factual settings. Understanding how courts have applied the three-part test in different contexts helps to illustrate both the power and the boundaries of this cause of action.

Mistaken Payments and Transfers. The simplest and most frequently litigated category of unjust enrichment involves the transfer of money under mistake. Where a plaintiff pays money to a defendant in the mistaken belief that a debt is owed (whether by reason of erroneous accounting, a forged cheque, or an overpayment), the three elements are easily established. Money is an incontrovertible benefit; the plaintiff's deprivation corresponds precisely to the defendant's enrichment; and the plaintiff's intention was vitiated by mistake, leaving no valid juristic reason. Restitution follows unless the defendant can establish a change of position or other defence.

Domestic and Cohabitation Disputes

Unjust enrichment has a significant role in disputes arising from the breakdown of domestic partnerships, particularly where the parties were not married and family property legislation does not apply. A cohabiting partner who, over many years, contributed domestic services, childcare, labour on property, or direct financial contributions to assets held in the other's name may bring a claim in unjust enrichment. The services constitute an enrichment of the property-holding partner; the deprivation corresponds to the services provided; and in the absence of donative intent or other juristic reason, restitution, typically by way of constructive trust or quantum meruit, is available.

Kerr v. Baranow remains the leading authority governing unjust enrichment claims in the domestic context. Cromwell J.'s judgment confirmed the unified analytical framework, clarified the role of "common intention" constructive trusts, and addressed how mutual benefit situations should be analyzed without resort to the impermissible shortcut of rough offsetting.

Commercial Fraud and Misappropriation

Unjust enrichment is a powerful tool where funds or property have been obtained through fraudulent misrepresentation, breach of fiduciary duty, or knowing receipt of funds wrongfully diverted. In such cases, unjust enrichment may be pleaded alongside the underlying tort or equitable wrong, providing access to a broader range of remedies (including constructive trust and equitable tracing through commingled assets) than a simple compensatory damages claim would permit.

In fraudulent diversion cases, courts will frequently pierce the intermediary arrangement and recognize a direct (or sufficiently corresponding) deprivation flowing from the plaintiff to the ultimate recipient. As confirmed by the Supreme Court in Alberta v. Elder Advocates of Alberta Society, there is no prohibition on restitution against indirect recipients in Canadian law.

Failed Contracts & Property Improvements

Failed or invalid contracts. Where parties perform under what they believe to be a binding agreement, but the agreement turns out to be void, unenforceable, or fundamentally breached, unjust enrichment may provide relief. The failure of the contractual purpose negates what would otherwise be the juristic reason for the transfer. This situation, historically analyzed as "failure of consideration" or "total failure of basis," is now properly analyzed under Garland as the negation of an ostensible contractual juristic reason. A plaintiff who paid a deposit on a contract that never proceeded, or who performed services under an agreement that was void for uncertainty, may recover on this basis.

Property improvements and capital contributions. A party who improves another's property, whether by renovating a home, paying down a mortgage, or making capital investments, may claim unjust enrichment where no contract or donative intent explains the contribution. The analysis depends on whether the improvements constitute an enrichment that is incontrovertible (typically, because they have created a realizable increase in the property's market value), whether the plaintiff suffered the corresponding deprivation (by expending time, money, or both), and whether any juristic reason (such as a prior agreement or understood gift) explains the contribution.

Canadian courts have been notably willing to impose liability in the property context. Landowners may face substantial restitutionary awards where a plaintiff's contribution to real property generates a measurable financial benefit, and courts have regularly imposed constructive trusts over improved real property where a personal award would be inadequate to reflect the plaintiff's contribution.