Unjust enrichment is a legal institution that describes a situation in which one person's assets are unfairly increased at the expense of another, without any valid legal reason. This occurs when one party's assets increase while the other party suffers a material loss, even though there is no contractual or legal obligation between them. The legal system offers a secondary remedy to the aggrieved party when there is an unjust enrichment not protected by contract or tort provisions.

The legal basis for unjust enrichment is regulated in Articles 77 to 82 of the Turkish Code of Obligations ("TCO"). This regulation positions unjust enrichment as a third source of obligation, alongside contracts and torts, making it one of the fundamental principles of obligations law. TCO Article 77, unlike Article 61 of the former Code of Obligations, explicitly states that enrichment can occur not only through "assets" but also through "labor." This expansion is a significant innovation that increases the scope of legal protection. The main purpose of the unjust enrichment institution is to balance asset transfers or value increases that are not based on a valid reason and to ensure justice within the legal order by preventing unjust enrichment.

Unjust enrichment holds a special place among obligations arising from law, ranking after contracts and torts in obligations law. This institution is considered a "secondary" or "subsidiary" source of obligation. This means it comes into play when an asset transfer or loss cannot be remedied through another legal avenue. Supreme Court decisions also emphasize that an unjust enrichment lawsuit cannot be filed if another claim is primarily possible.

At the heart of unjust enrichment lies the "principle of compensatory justice." This principle states that a person who increases their assets by benefiting from another's assets or labor without a just cause is obliged to return the acquired gain and has a genuine obligation to restore the prior condition. This source of obligation functions as a critical "safety net" in Turkish private law, highlighting its scope and importance. The legal system offers this institution as a last resort for situations not covered by contractual relationships or torts, but where an unjust shift in value has occurred. The inclusion of the concept of "labor" in TCO Article 77 within the scope of enrichment indicates that the concept of assets has expanded. This reflects the law's effort to compensate not only for unjust gains on tangible goods but also for more abstract value shifts, such as when a person's labor goes uncompensated. This situation demonstrates a continuous evolution by the legislator and the judiciary to fill legal gaps and expand the principle of "compensatory justice," thereby ensuring more comprehensive justice. This "safety net" function indicates to legal practitioners that when evaluating a legal issue, they should first investigate primary sources of obligation like contracts or torts, but if these avenues are closed, unjust enrichment becomes an important alternative. This reinforces the institution's flexibility and its complementary role in the legal system's pursuit of justice.

1. Essential Elements of Unjust Enrichment

For an unjust enrichment lawsuit to be filed and successful, four fundamental conditions must be met simultaneously. These conditions determine the "unjust" nature of the imbalance in the legal relationship and the emergence of the obligation to return.

1.1. Enrichment: Scope of Increase in Assets

First, there must have been an increase in the defendant's assets, i.e., enrichment. Enrichment can occur as an increase in assets (e.g., money mistakenly deposited into an account) or a decrease in liabilities (e.g., a debt mistakenly paid by someone else). The values that can be subject to enrichment are not limited. According to Article 77 of the Turkish Code of Obligations, enrichment can occur from another person's property or labor. In this context, all kinds of property, services, rights, tangible or intangible assets, opportunities, and advantages can be subject to unjust enrichment. Furthermore, if an asset should have decreased but did not, without a just cause, this maintenance of the existing situation is also considered unjust enrichment.

1.2. Impoverishment: Nature of Decrease in Assets

Parallel to enrichment, there must have been a decrease, or impoverishment, in the plaintiff's assets. While the classical view strictly requires impoverishment as an absolute condition, some newer views argue that direct impoverishment is not necessary for unjust enrichment to occur, and that "a decrease in another person's assets or labor" is sufficient for the obligation to arise.

This situation indicates that the institution of unjust enrichment is interpreted to encompass not only a direct "loss-gain" equation but also the unfair diminution of a person's assets or labor. This nuance is related to the law adopting a broader understanding of justice. For example, if a person's labor goes uncompensated (such as a service performed without a contractual relationship and without payment), even if it's not a direct "impoverishment," it can be considered a decrease in assets. This increases the institution's applicability to situations where not only tangible assets but also abstract values and potential gains are unjustly transferred. This doctrinal debate may provide flexibility in the future interpretation of the "impoverishment" condition in Supreme Court decisions and could expand the scope of unjust enrichment lawsuits, especially in new-generation value transfers like intellectual property, data usage, or uncompensated services. It is crucial for legal practitioners to develop litigation strategies by considering this expanded concept of "decrease."

1.3. Causal Link: Causation Between Enrichment and Impoverishment

There must be a causal link between the event leading to enrichment and its result. If this link cannot be established, unjust enrichment is not deemed to have occurred. In unjust enrichment, a "natural causal link" is sufficient, and there is no need to seek an "adequate causal link" as in torts.

1.4. Absence of a Just Cause: The "Unjust" Condition

The increase in assets not being based on a just, lawful, and valid cause is the most fundamental and distinctive condition of unjust enrichment. If the enrichment is based on a legitimate cause, it is no longer "unjust" and cannot be subject to a lawsuit. The absence of a just cause is primarily regulated in four situations in TCO Articles 77 and 78:

• Invalidity of the Cause: In situations where a legal transaction is contrary to morality, the transaction is invalid, and the benefits made based on this transaction constitute unjust enrichment.
• Failure of the Cause to Materialize: This occurs when a benefit is given in anticipation of an event that has not yet materialized but is expected to (e.g., fiancés giving gifts to each other in anticipation of marriage, and the marriage not occurring).
• Termination of the Cause: In cases like contract annulment or rescission, the cause terminates, and the benefits made must be returned.
• Performance of a Non-Owed Obligation (Condictio Indebiti): This is the situation where a person, mistakenly believing they owe a debt, performs an obligation even though they are not actually indebted.

The "absence of a just cause" is not merely a technical legal deficiency; it also demonstrates the law's strong connection with fundamental moral values. A transaction being contrary to morality renders it legally invalid and makes the enrichment based on it "unjust." TCO Article 81, which states that "what has been given for the purpose of bringing about an unlawful or immoral result cannot be reclaimed," but that "the judge may decide to appropriate such thing to the state," presents the sharpest expression of this moral dimension. The law discourages such actions by not mediating the return of benefits made for immoral purposes. However, at the same time, it allows for state intervention to prevent the unjustly enriched party from benefiting from this situation. This emphasizes that the law aims to protect not only individual interests but also the general moral and legal order of society. This situation indicates that lawyers should evaluate not only the legal validity but also the moral dimension of their clients' actions. In unjust enrichment lawsuits arising from immoral transactions, the risk of the return claim being rejected and even the property being confiscated by the state should be an important cautionary element in legal counseling.

Concept	Definition	Scope / Nuance
Enrichment	Increase in assets (increase in active assets / decrease in liabilities)	Goods, labor, services, rights, opportunities, advantages; maintaining the current situation
Impoverishment	Decrease in assets (decrease in assets / labor)	"Decrease" in assets is sufficient instead of direct loss (doctrinal debate)
Causation	Cause-and-effect relationship between enrichment and impoverishment	Natural causation is sufficient
Absence of Just Cause	Lack of a legally valid basis	Invalidity of the cause (contrary to morality), non-fulfillment, termination, performance of an unowed obligation

2. Types of Unjust Enrichment and Special Cases

2.1. Enrichment by Performance (Condictio Indebiti: Performance of a Non-Owed Obligation)

Among enrichments by performance, the most common type is "condictio indebiti," which is a claim for unjust enrichment based on the performance of a non-owed obligation. This situation is specifically regulated in Article 78 of the Turkish Code of Obligations. According to this provision, if a person, mistakenly believing they owe a debt, performs an obligation voluntarily (by falling into error), they can demand the return of the performance.

TCO Article 78 introduces a limitation for unjust enrichment claims: if a person performs knowing or suspecting that they do not owe the debt, the claim for restitution is prevented. This emphasizes that the person must act with "causa solvendi" (intention to perform a debt), not "causa donandi" (intention to donate). Situations such as the performance of an invalid contract, performance when there is a valid defense, or performance of an obligation subject to a suspensive condition before the condition is met fall under this scope. The situation of performing more than the amount agreed upon in a valid contract can also be considered within the scope of condictio indebiti.

The "mistake" condition in the condictio indebiti institution is not merely a technical element but also a fundamental principle that protects the reliability and consistency of legal transactions. The law prevents a person from later claiming that a performance they made knowingly and willingly was "unjust," as this would contradict their own behavior. This demonstrates the importance the law attaches to individuals' declarations of will and actions; the subsequent reclamation of a deliberately given benefit would undermine legal certainty. This reveals that the law considers not only material justice but also consistency and honesty in individuals' actions. This situation increases the importance of the burden of proof in condictio indebiti lawsuits. It is vitally important for the plaintiff to prove that they were truly in error when making the payment. Otherwise, they risk their lawsuit being dismissed. This emphasizes the necessity for legal professionals to advise their clients to carefully confirm their debt status before making payments.

2.2. Enrichment Outside of Performance

This category covers situations where one party's assets increase at the expense of another without any performance relationship between the parties. For example, receiving a valuable product that does not belong to you due to a cargo company's error and not returning it, or a person mistakenly finding and spending an amount of money belonging to someone else, falls into this category. In these situations, the enrichment is not based on a performance but occurs as a result of direct intervention or coincidence.

2.3. Imperfect Obligations and Irretrievable Cases (TCO Article 81)

The performance of imperfect obligations does not constitute unjust enrichment, and the performance cannot be reclaimed. This is because, in imperfect obligations, there is a legally valid debt, but it cannot be claimed through a lawsuit or enforcement. In this context:

• Time-Barred Debts: If a time-barred debt is paid without raising the defense of statute of limitations, it cannot be reclaimed.
• Fulfillment of a Moral Duty: Enrichments arising from the fulfillment of a moral duty also cannot be reclaimed. In this case, the performance is considered to have been made with the intention of donation.
• Gambling and Betting Debts: According to TCO Article 604, gambling and betting debts are imperfect obligations, and payments made for these debts cannot be reclaimed.

What has been given for the purpose of bringing about an unlawful or immoral result cannot be reclaimed (TCO Article 81). This is a consequence of the principle that the law does not protect transactions serving illegal or immoral purposes. However, in such cases, the judge may decide to appropriate the given thing to the state.

This provision (TCO Article 81) reflects the strong public policy of the law, which not only ensures justice between individuals but also protects public order and morality. By not assisting parties through restitution in transactions that serve an illegal or immoral purpose, the law discourages such actions. However, at the same time, it prevents unjust enrichment from such actions. The decision to appropriate the property to the state prevents either the offending parties or those who benefit from the action from profiting, demonstrating the law's commitment to protecting the rule of law and moral values. This is proof that even private law can transcend individual rights when public interest and moral norms are at stake. This situation indicates that legal professionals should meticulously examine not only the legal validity of their clients' transactions but also their conformity with public order and morality. Otherwise, clients may face the risk of having their claim for restitution rejected and even losing their assets to the state. This emphasizes the importance of ethics and social responsibility in legal counseling.

3. Scope and Limits of the Obligation to Restitute

The scope of the obligation to restitute arising from unjust enrichment differs depending on whether the enriched party acted in good faith, and the principle of "compensatory justice" plays a central role in determining this scope.

3.1. Principle of Restitution in Kind and Restitution of Value

As a rule, the unjustly enriched party is obliged to return the subject of enrichment in kind. This is a reflection of the principle of restoration. In situations where restitution in kind is not possible (e.g., if the property is consumed, destroyed, or transferred), the enriched party is obliged to return the value of the property.

3.2. Liability of the Good Faith Enriched Party and Claims for Expenses

A good faith enriched party is a person who did not know or was not required to know that the enrichment was not based on a just cause, and therefore did not know or was not required to know that there was an obligation to return. A good faith enriched party is responsible for the amount of enrichment still existing in their assets at the time the restitution of the subject of enrichment is demanded, meaning the amount they have not yet disposed of. In other words, they are discharged from their obligation by returning what they still possess.

A good faith enriched party has the right to claim "necessary" and "useful" expenses incurred on the subject of enrichment from the claimant. Necessary expenses are costs incurred for the preservation and maintenance of the thing. Useful expenses are costs that increase the value of the thing or facilitate its use. For example, if a person unknowingly enriches an automobile by having it painted, they can claim the cost of this painting. However, to claim these expenses, they must have acted in good faith when incurring them. A good faith enriched party cannot claim "luxury" expenses. Additionally, they have the right to remove additions that can be detached without damaging the main part before returning it. Especially in money debts, there are differing views among Supreme Court chambers regarding the scope of the good faith enriched party's obligation to return. Some chambers argue that spending the money does not extinguish the obligation to return, while others state that social considerations may influence the exercise of discretionary power.

3.3. Liability of the Bad Faith Enriched Party and Claims for Expenses

A bad faith enriched party is someone who knew or should have known that the enrichment was not based on a just cause, and therefore knew or should have known that there was an obligation to return. The bad faith party's obligation to return is to return the entire enrichment. The enriched party is also responsible for the parts they have disposed of. A bad faith enriched party can only claim necessary expenses, and only the value increase existing at the time of restitution for useful expenses. They cannot claim luxury expenses. For example, if a bad faith enriched party buys a car and spends 100,000 TL on it, and 5 years later, when restitution is demanded, the car's value has fallen to 20,000 TL, they can only claim 20,000 TL. A bad faith enriched party may be liable to pay interest from the date of enrichment; no notice is required for them to fall into default.

The distinction between good faith and bad faith is not merely a classification in unjust enrichment law, but a fundamental spectrum that determines the degree of liability. The phrase "should have known" includes an objective duty of care beyond subjective knowledge, which broadly defines the limits of good faith. The Supreme Court's differing approaches, especially regarding the liability of a good faith enriched party in consumable assets like money, demonstrate the law's attempt to find a balance between strict rules and equity and social realities. This shows that the law is sensitive not only to abstract principles but also to the specifics of concrete cases and societal impacts. When filing or defending a lawsuit, proving whether the enriched party acted in good faith or bad faith can fundamentally affect the outcome of the case. Especially the "should have known" criterion requires lawyers to consider not only direct knowledge but also what a reasonable person in that situation should have known when evaluating their clients' circumstances. While differing views in the Supreme Court create legal uncertainty, they also offer lawyers the flexibility to develop different arguments in specific situations.

3.4. The Role of the Principle of Compensatory Justice: Restitution of Real Value

The principle of compensatory justice aims to ensure the full restitution of values transferred from one party's assets to another's without a just cause. This means a true obligation to restore the prior condition. Especially in inflationary economic conditions, where money loses value over time, the restitution of only the nominal amount can lead to great injustices. In such cases, according to Supreme Court decisions, in accordance with the principle of compensatory justice, the scope of the restitution obligation should be determined by considering the real value at the time of restitution. This aims to bring the purchasing power of the money paid back to its purchasing power at the initial payment date. The Supreme Court, especially in cases where the price in real estate sales is fraudulently understated, applies the principle of compensatory justice to rule on the restitution of the real value.

The principle of compensatory justice is a dynamic mechanism that adapts unjust enrichment law to economic realities. The law is not content with merely restituting nominal values but aims to compensate the victim's real loss by considering changes in the purchasing power of money. This demonstrates the law's capacity not only to rectify a past situation but also to remedy injustices created by current economic conditions. This principle is a vital tool for fair outcomes in unjust enrichment lawsuits, especially during periods of high inflation, and showcases the legal system's ability to adapt to societal and economic dynamics. In countries with high inflation or in lawsuits spanning long periods, legal professionals must strengthen their arguments with expert reports and current valuation assessments, considering not only the initial nominal value but also inflation rates, exchange rates, or increases in the market value of the relevant asset when determining the amount to be restituted. Otherwise, the client's real loss may not be compensated.

4. Legal Nature of Unjust Enrichment Lawsuit and Its Relationship with Other Lawsuits

The unique characteristics of an unjust enrichment lawsuit and its relationship with other sources of obligation are critically important in determining the legal strategy.

4.1. Personal Nature: A Claim Attached to a Person

A claim for unjust enrichment gives rise to a personal (relative) right to claim. This means that the lawsuit can only be filed against the unjustly enriched person or their heirs. It cannot be asserted against third parties. For an obligation to arise from unjust enrichment, neither the impoverished nor the enriched party needs to have legal capacity; legal personality is sufficient to be a party. This feature is a result of the institution's function of providing compensatory justice. If the enriched party has gone bankrupt and the asset subject to enrichment is in the bankruptcy estate, the plaintiff cannot demand restitution in kind; the restitution claim converts into a monetary claim and is recorded in the bankruptcy estate.

The absence of a capacity requirement indicates that the primary purpose of the unjust enrichment institution is to rectify unfair shifts between assets rather than to regulate liabilities arising from individuals' voluntary actions. This emphasizes that the law focuses on preventing even entities without discernment (e.g., minors, mentally ill individuals) or legal entities that lack their own will from unjustly enriching or impoverishing themselves. This proves that the law seeks objective justice and balance, regardless of individuals' subjective situations. In this way, the property rights of even those without the capacity to undertake legal transactions are protected, and unjust gains are prevented. This feature significantly broadens the applicability of unjust enrichment lawsuits. Especially in cases where incapacitated persons are parties or where a legal transaction is invalid due to lack of capacity, unjust enrichment may be the only legal recourse. This indicates that lawyers should consider unjust enrichment as a solution in situations involving capacity issues.

4.2. Subsidiary (Secondary) Nature Debate and Doctrinal Views: A Matter of Priority

Unjust enrichment provides a subsidiary legal protection. If another primary protective remedy is available (e.g., an action for restitution of possession, a claim arising from a contract, a tort claim), an unjust enrichment lawsuit cannot be filed. There are different views on this matter in doctrine:

• Subsidiary Nature View: This view expresses concern that allowing unjust enrichment lawsuits to be easily filed when another action is available would "accustom the judiciary and parties to laziness." Case law in French law also supports this view.
• Independence View (Reisoğlu): According to this view, the institution of unjust enrichment is entirely independent of other institutions and can compete with other claims when its specific conditions are met.
• Competition View: Some doctrinal views accept that unjust enrichment lawsuits can compete with tort and unauthorized agency lawsuits.

The "subsidiary nature" principle is one of the fundamental pillars of the Turkish legal systematic and aims to ensure legal certainty. This principle emphasizes that each legal institution serves a specific purpose and has its own specific conditions. If there is a more specific and direct legal avenue, using it ensures that the litigation is more predictable and effective and provides a solution appropriate to the nature of the relevant legal relationship. The "laziness" argument expresses a concern for the preservation of this systematic and the seriousness of legal processes. This principle reveals that the law attaches importance not only to results but also to process and systematic. For legal professionals, this creates the necessity of meticulously analyzing all possible legal avenues before filing a lawsuit. Choosing the wrong type of lawsuit can lead to the dismissal of the lawsuit and the client's loss of rights. Therefore, the "subsidiary nature" principle serves as an important threshold that tests lawyers' depth of legal knowledge and analytical abilities.

4.3. Comparison with Tort: Purpose and Fault Difference

While a tort aims to compensate for the decrease (damages) in the victim's assets, unjust enrichment aims to restitute the enrichment that occurred in the enriched party's assets at the expense of the claimant. In a tort lawsuit, the defendant's fault is generally sought, whereas in an unjust enrichment lawsuit, it is not required for the enriched party to be at fault. Furthermore, unjust enrichment is not subject to any capacity requirements; tort liability generally requires legal capacity. In both situations, interest may be applied from the date the event (enrichment or tort) occurred; no notice is required for default.

4.4. Comparison with Claims Arising from Contract: Principle of Priority

If there is a valid contractual relationship between the parties and a claim arising from this contract is possible, an unjust enrichment lawsuit cannot be filed. For example, unpaid rent is not a matter of unjust enrichment but a claim arising from a lease agreement. In cases where more than the amount agreed upon in the contract is performed, whether the claim for restitution should be based on unjust enrichment or contractual liability is debated in doctrine. The Supreme Court tends to accept that in some cases, overpayments are subject to contractual liability provisions.

4.5. Comparison with Action for Restitution of Possession: Real Right vs. Personal Right

While an unjust enrichment lawsuit is based on a personal (relative) right, an action for restitution of possession is based on a real (absolute) right, namely the right of ownership. An unjust enrichment lawsuit is based on the assumption that ownership has passed to the enriched party. An action for restitution of possession, on the other hand, grants the owner the right to demand restitution based on the assumption that ownership still remains with the original owner. Therefore, these two lawsuits cannot coexist. Unjust enrichment can only be filed against the enriched party or their heirs, whereas an action for restitution of possession can be asserted against anyone violating the right of ownership. Unjust enrichment lawsuits are subject to 2/10 year limitation periods, while actions for restitution of possession are generally not subject to limitation periods.

4.6. Difference from Unauthorized Agency: Intent and Purpose

In unauthorized agency, a person consciously and voluntarily intervenes in another's legal sphere for their benefit. In unjust enrichment, only the unjust transfer of value is essential, and no specific intent (acting for another's benefit) is required.

Criteria	Unjust Enrichment	Tort	Claim Arising from Contract	Action for Recovery of Property (Reivindicatory Action)	Unauthorized Management of Affairs (Negotiorum Gestio)
Primary Purpose	Restitution of unjust enrichment	Compensation for damages	Performance of contractual obligation	Recovery of ownership	Compensation for managing another's affairs/expenses
Fault/Unlawfulness Requirement	No fault required; unjust enrichment is sufficient	Generally requires fault	Breach of contract	Unlawful possession of property	Management of affairs on behalf of another
Capacity Requirement	No legal capacity required; legal personality is sufficient	Generally requires legal capacity	Requires legal capacity	Legal personality is sufficient	Requires legal capacity
Nature (Personal/Real)	Personal (relative)	Personal (relative)	Personal (relative)	Real (absolute)	Personal (relative)
Subsidiary Nature	Yes (cannot be filed if other avenues exist)	No (primary)	No (primary)	No (primary)	Can compete (doctrinal debate)
Statute of Limitations	2 years (from knowledge)/10 years (from event)	2 years (from knowledge)/10 years (from event) (longer criminal statute of limitations may apply)	General 10 years (special provisions may apply)	Not subject to statute of limitations	General 10 years
Ownership Status	Ownership has passed to the enriched party	Ownership status may change	Ownership status may change	Ownership remained with the original owner	Ownership status may change

5. Litigation Process and Procedural Provisions

Unjust enrichment lawsuits are in the nature of claims for debt and are heard in the Civil Courts of First Instance, which are courts of general jurisdiction, with written proceedings. However, in unjust enrichment lawsuits arising from negotiable instruments, the Commercial Courts of First Instance have jurisdiction. The competent court, according to Article 6 of the Code of Civil Procedure ("CCP"), is the court of the defendant's (real or legal person) domicile at the time the lawsuit is filed.

The plaintiff must prove that the opposing party was unjustly enriched and that their own assets suffered a corresponding loss. The defendant, if they argue that there was a just cause (e.g., "this money was a debt payment"), must prove it. The court decides whether the conditions are met in light of the evidence presented. In Turkish law, the principle of "he who alleges must prove" generally applies.

5.1. Statute of Limitations in Unjust Enrichment Lawsuits

Claims arising from unjust enrichment are subject to specific statutes of limitations. Article 82 of the Turkish Code of Obligations provides for two separate limitation periods: two years from the date the creditor learns of the right to reclaim and, in any case, ten years from the date the enrichment occurred. If a lawsuit is not filed within these periods, the right to claim arising from unjust enrichment becomes an imperfect obligation. A time-barred claim becomes legally unenforceable, and the defendant may assert the defense of statute of limitations.

The two-year period begins when the creditor definitively learns the identity of the enriched person, that the enrichment belongs to them, and its amount. This learning must be certain enough to enable the filing of a lawsuit, not merely speculative. For public institutions, the statute of limitations begins from the date the institution's approval authority learns of the right to reclaim.

The ten-year period, on the other hand, begins at the moment the enrichment event occurs and is an absolute period. This period begins to run at the moment the right to claim arises, and the starting date may vary depending on the type of enrichment. For example, in performance-based enrichments, if the enrichment existed from the beginning without a valid cause, the ten-year period begins at the time of performance. In situations where the cause failed to materialize, it begins when it is definitively understood that the cause will not materialize; in situations where the cause subsequently ceased to exist, it begins when the cause ceased to exist. In enrichments arising from tort or the enriched party's intervention, it begins at the time the tort or intervention occurred. In continuously ongoing enrichments, it begins when the enrichment ends.

Statute of limitations periods are subject to the general limitation provisions of the Turkish Code of Obligations; that is, these periods can be suspended or interrupted. For example, if the debtor acknowledges the debt or the creditor files a lawsuit or initiates enforcement proceedings, the statute of limitations is interrupted, and a new period begins to run.

Recently, as in many debt lawsuits, the institution of mediation has become involved in unjust enrichment lawsuits. Parties can resort to the institution of mediation to resolve the dispute before going to court. This allows legal processes to be resolved more quickly and cost-effectively.

6. Conclusion

The unjust enrichment lawsuit, regulated in the Turkish Code of Obligations, is a fundamental source of obligation aimed at ensuring justice within the legal order. It functions as a "safety net" in situations where primary sources of obligation like contracts and torts are insufficient, aiming to correct asset shifts that occur without a just cause. The principle of compensatory justice, which underlies the institution, reveals the law's ability to adapt to economic realities, especially in inflationary conditions, by ensuring the restitution of real value beyond nominal restitution.

For the lawsuit to be filed, the existence of four fundamental conditions is essential: enrichment, impoverishment, a causal link, and the absence of a just cause. The doctrinal expansion in the interpretation of the "impoverishment" condition and the moral dimensions of the "absence of a just cause" demonstrate how deeply the institution is intertwined with not only technical aspects but also the understanding of social justice. The distinction between good faith and bad faith is a central element that radically affects the scope of the restitution obligation, and proving this distinction is determinative of the outcome of the lawsuit.

The unjust enrichment lawsuit differs from other sources of obligation by its personal nature and its subsidiary (secondary) character. This subsidiary nature is of great importance for maintaining legal systematics and ensuring the effectiveness of legal processes. The differences from similar institutions such as tort, claims arising from contract, and actions for restitution of possession provide a critical guide for choosing the correct legal path. Features such as the absence of a capacity requirement prove that the law seeks an objective balance independent of individuals' subjective situations.

In conclusion, the unjust enrichment lawsuit is an indispensable tool for establishing justice in complex legal relationships. It is vitally important for legal practitioners to deeply understand the fundamental principles, elements, types, scope of restitution, and relationship with other legal avenues of this institution to effectively protect their clients' rights and determine correct strategies in legal processes.