Under the Philippine Civil Code, what is unjust enrichment, what are the requisites of an action to recover based on unjust enrichment (accion in rem verso) under Article 22, how does unjust enrichment differ from solutio indebiti and from a quasi-contract, and when is a person who acquires or comes into possession of something at another's expense without just or legal ground bound to return it or to indemnify the other? Cite the governing statutory provisions (Articles 22 to 23) and the leading Supreme Court decisions.

Answer Summary

The Civil Code codifies the principle that no person shall be unjustly enriched at the expense of another. The general action for unjust enrichment, known as accion in rem verso, is governed by Article 22 of the Civil Code. A person who acquires or comes into possession of something at another’s expense without a just or legal ground is obliged to return the same. Where an act or event causes damage to property — even without fault or negligence — Article 23 imposes liability for indemnity if the defendant derived a benefit from that act or event. Unjust enrichment is distinguished from the quasi-contract of solutio indebiti (Article 2154), which requires a mistaken payment, and from quasi-contracts generally (Article 2142), which arise from lawful, voluntary, and unilateral acts intended to prevent unjust enrichment. The Supreme Court has consistently held that accion in rem verso is a subsidiary remedy — available only when no other action based on contract, quasi-contract, crime, or quasi-delict exists.

The controlling statutory provisions are Articles 22 and 23 of the Civil Code. The leading Supreme Court decision on the definition and requisites of unjust enrichment under Article 22 is Carlos A. Loria v. Ludolfo P. Muñoz, Jr., G.R. No. 187240, 15 October 2014, which articulated the two conditions for unjust enrichment and held that the prevention of unjust enrichment overrides the doctrine of in pari delicto. The subsidiary nature of accion in rem verso is reiterated in Republic v. Court of Appeals, Magallanes v. Sun Life Assurance Co. of Canada, and National Power Corporation v. Benguet Electric Cooperative, Inc., G.R. No. 218378, 14 June 2021. For quasi-contracts, Republic v. Davao Contractors Development Cooperative (DACODECO), G.R. No. 210029, 20 November 2017, confirmed that the enumeration in Articles 2144–2175 is not exclusive and that a quasi-contractual relation may be forced upon the parties to avoid unjust enrichment. The most recent decision, Frian B. Lambo v. Evelyn Vega-Rose, G.R. No. 269085, 19 February 2026, applied solutio indebiti to compel reimbursement and underscored that no person should be allowed to enrich themselves at another’s expense.

The essential elements of accion in rem verso are: (1) the defendant has been enriched; (2) the plaintiff has suffered a corresponding loss; (3) the enrichment has no just or legal ground; and (4) the plaintiff has no other available remedy under contract, quasi-contract, crime, or quasi-delict. The enrichment and impoverishment must be correlative — directly linked.

The most frequent reason a claim fails is the availability of another remedy. If a contract, a quasi-contract (like solutio indebiti), or a tort action exists, the party must pursue that remedy first. Accion in rem verso cannot be used to circumvent the preclusive effect of an existing agreement or to revive a lost cause of action. In Central Bank of the Philippines v. Court of Appeals, the claim was denied because a specific remedy under the Central Bank Act was available. In Uy v. Spouses Medina, the Supreme Court strictly applied the subsidiarity rule, denying recovery because the parties had a contractual relationship. Practitioners must therefore plead and prove the absence of any other remedy as an indispensable element.

Based on comprehensive database and web research, the most recent ruling on unjust enrichment principles is Lambo v. Vega-Rose (19 February 2026). No other rulings from 2024–2026 specifically interpreting Articles 22–23 or the requisites of accion in rem verso were identified; the legal framework remains settled with no legislative amendments.

Section I — Issue Overview

1. What is unjust enrichment under Articles 22–23, what are the requisites of accion in rem verso, and how does it differ from solutio indebiti and quasi-contracts? This is a question of civil law doctrine with practical consequences for pleading and pursuing restitutionary claims. Understanding the precise elements, the subsidiary character, and the boundaries between the general action and specific quasi-contracts determines which cause of action to plead and what evidence to present.

Section II — Legal Analysis

Issue 1: Unjust enrichment under Articles 22–23, requisites of accion in rem verso, and distinctions from solutio indebiti and quasi-contracts

Applicable Laws & Issuances

The governing statutory provisions are found in the Civil Code of the Philippines (Republic Act No. 386):

• Article 22. Every person who through an act of performance by another, or any other means, acquires or comes into possession of something at the expense of the latter without just or legal ground, shall return the same to him.
• Article 23. Even when an act or event causing damage to another’s property was not due to the fault or negligence of the defendant, the latter shall be liable for indemnity if through the act or event he was benefited.

These articles appear in Chapter 2 (Human Relations) of the Preliminary Title. Article 22 is the statutory foundation of the general prohibition against unjust enrichment and the action for restitution known as accion in rem verso. Article 23 creates a distinct, narrower liability — indemnity without fault — when property damage confers a benefit on the defendant.

The broader architecture of quasi-contracts is set out in Book IV, Title XVII:

• Article 2142. Certain lawful, voluntary and unilateral acts give rise to the juridical relation of quasi-contract to the end that no one shall be unjustly enriched or benefited at the expense of another.
• Article 2154 (on solutio indebiti): If something is received when there is no right to demand it, and it was unduly delivered through mistake, the obligation to return it arises.
• Article 2155: The recipient of a payment made by mistake is obliged to return what was received.

Case Law Analysis

Carlos A. Loria v. Ludolfo P. Muñoz, Jr., G.R. No. 187240 — 15 October 2014 (J. Peralta, Second Division)

Focus of Dispute: Whether Loria must return P2,000,000.00 to Muñoz under the principle of unjust enrichment codified in Article 22, after the promised government subcontract never materialized.

Facts: Muñoz advanced P2 million to Loria, who represented he could secure a subcontract of a river-dredging project. The project was awarded to a third company but no subcontract was given to Muñoz. Loria retained the money despite demand.

Arguments: Muñoz argued Loria held the money without just cause. Loria claimed the agreement was void and thus neither party could recover under the in pari delicto doctrine.

• Petitioner (Loria): The underlying agreement was illegal, so in pari delicto bars recovery.
• Respondent (Muñoz): Regardless of any defect, Loria has no right to retain the money; it would be unjust enrichment.

Disposition: The petition was denied; the Court of Appeals’ decision was affirmed with modification as to interest. Loria was ordered to return the P2,000,000.00.

Ratio Decidendi: The Court defined unjust enrichment and its two conditions:

“There is unjust enrichment ‘when a person unjustly retains a benefit to the loss of another, or when a person retains money or property of another against the fundamental principles of justice, equity and good conscience.’” “The principle of unjust enrichment has two conditions. First, a person must have been benefited without a real or valid basis or justification. Second, the benefit was derived at another person’s expense or damage.”

The Court held that even if the subcontract were void, the doctrine of in pari delicto would not bar recovery because “the prevention of unjust enrichment is a recognized public policy of the State,” an established exception. The Court quoted Gonzalo v. Tarnate, Jr. and emphasized that Article 22 explicitly requires return of something acquired without just or legal ground.

Evidence Evaluated: The check voucher signed by Loria acknowledging receipt of P1,200,000.00 and P800,000.00 was admitted. The trial and appellate courts found this sufficient to prove Loria’s receipt and his failure to justify any right to retain the money.

Precedential Status: This is the leading Supreme Court decision directly interpreting and applying Article 22. It remains good law and is frequently cited for the definition and conditions of unjust enrichment.

Republic v. Davao Contractors Development Cooperative (DACODECO), G.R. No. 210029 — 20 November 2017 (J. Leonen, Third Division)

Focus of Dispute: Whether DACODECO could sue DPWH under quasi-contract principles despite the absence of a direct contract between them, for work done on water system projects.

Facts: Barangay captains awarded water system projects to DACODECO. After DACODECO had completed 45% of the work, the DPWH District Engineer ordered it stopped, asserting the barangay captains lacked authority. DPWH later re-bid the projects without provision for DACODECO’s completed work. DPWH is the implementing agency and processes payments.

Arguments: The OSG argued that a quasi-contract could not arise because DACODECO’s acts were not “voluntary and unilateral” — they were performed under contracts with barangay captains.

• Petitioner (Republic): No contractual privity exists; DACODECO’s remedy, if any, lies against the barangay captains.
• Respondent (DACODECO): DPWH would be unjustly enriched if it awarded full payment to the new contractor while disregarding the value of DACODECO’s completed work.

Disposition: The petition was denied; the Court of Appeals decision affirming denial of DPWH’s motion to dismiss was affirmed in toto.

Ratio Decidendi: The Court anchored its decision on Article 2142, which declares that certain lawful, voluntary and unilateral acts give rise to a quasi-contractual relation to prevent unjust enrichment. Citing Philippine National Bank v. CA (291 Phil. 356):

“[T]he Civil Code does not confine itself exclusively to the quasi-contracts enumerated from Articles 2144 to 2175 but is open to the possibility that, absent a pre-existing relationship, there being neither crime nor quasi-delict, a quasi-contractual relation may be forced upon the parties to avoid a case of unjust enrichment.” The Court rejected the argument that DACODECO’s acts were not “voluntary and unilateral” because the concept includes acts executed even without a pre-existing contract when they result in benefits.

Evidence Evaluated: DACODECO alleged 45% project completion; DPWH admitted it processes payments. The Court found that allowing DPWH to award the full amount to the new contractor without ascertaining liability to DACODECO would amount to unjust enrichment and inequity, sufficient to survive a motion to dismiss.

Precedential Status: Good law. It confirms that the quasi-contracts enumerated in the Civil Code (including solutio indebiti) are not exhaustive and that Article 2142 serves as the general premise for imposing obligations to prevent unjust enrichment.

Frian B. Lambo v. Evelyn Vega-Rose, G.R. No. 269085 — 19 February 2026 (J. Gaerlan, First Division)

Focus of Dispute: Whether petitioner must reimburse respondent for settling petitioner’s delinquent housing loan to prevent foreclosure, under the principle of solutio indebiti.

Facts: Respondent paid ₱3,625,607.75 to the Home Development Mutual Fund (HDMF) to fully settle petitioner’s delinquent loan, saving her property from foreclosure. Petitioner later claimed no valid contract of sale or equitable mortgage existed and refused to reimburse.

Arguments:

• Petitioner: No valid contract existed, so she is not obligated.
• Respondent: The payment extinguished petitioner’s debt and benefitted her; retention without reimbursement constitutes unjust enrichment.

Disposition: Petition denied; CA decision affirmed. Petitioner must reimburse respondent.

Ratio Decidendi: The Court held that even assuming the underlying agreement was defective, the petitioner would still be liable under solutio indebiti. Citing Article 1236 on third-party payment, the Court stated:

“To allow petitioner to retain the benefits of respondent’s payment while refusing to reimburse her would contravene the basic principle against unjust enrichment. No person should be allowed to enrich themselves at the expense of another.”

Evidence Evaluated: Official Receipt No. 9623995 and an Acknowledgment Receipt signed by petitioner’s brother proved the payment; the benefit to petitioner was undisputed.

Precedential Status: The most recent pronouncement (2026) linking solutio indebiti to the broad principle against unjust enrichment. It confirms that Article 22’s underlying policy is pervasive.

Dometila M. Andres v. Manufacturers Hanover & Trust Corp., G.R. No. 82670 — 15 September 1989 (J. Griño-Aquino, First Division) and Sebastian Siga-an v. Alicia Villanueva, G.R. No. 173227 — 20 January 2009 (Third Division)

Both cases are resolved exclusively under Article 2154 (solutio indebiti) and illustrate the distinct remedies. Andres ordered restitution of a duplicate telegraphic transfer mistakenly sent by the bank; Siga-an ordered return of excessive interest payments made without a written stipulation. Neither discusses Article 22. They serve as concrete examples of the specific quasi-contract of solutio indebiti — where a payment is made by mistake without a duty to pay — and demonstrate that when the facts fit Article 2154, that is the proper cause of action, not the general accion in rem verso.

Doctrinal Synthesis

The current legal position, drawn from the statutes and jurisprudence, can be summarized as follows:

1. Unjust enrichment under Article 22 is a broad equitable principle: when a person retains a benefit to another's loss without valid basis, the law compels restitution. The Supreme Court’s two-fold test (Loria) — benefit without justification, and benefit at another’s expense — is the operational standard.

2. Accion in rem verso is the civil action to enforce Article 22. It is characterized by four strict requisites, confirmed by multiple authorities: (a) enrichment of the defendant; (b) impoverishment of the plaintiff; (c) absence of just or legal cause; and (d) subsidiarity — no other remedy under contract, quasi-contract, crime, or quasi-delict is available. The enrichment and impoverishment must be correlative (directly linked). The requirement of subsidiarity is the defining feature that distinguishes accion in rem verso from all other restitutionary actions. Central Bank of the Philippines v. Court of Appeals originally articulated this, and National Power Corporation v. Benguet Electric Cooperative, Inc., G.R. No. 218378, 14 June 2021, reiterated it in a recent application.

3. Solutio indebiti (Article 2154) is a species of quasi-contract. It applies when: (a) a payment or delivery is made; (b) the payor had no duty to make it; and (c) the payment was made by mistake. The recipient’s obligation to return arises without need of any other contract. Unlike accion in rem verso, solutio indebiti does not require proof of subsidiarity because it is itself a specific remedy provided by law. The critical differentiator is mistake: in solutio indebiti there is a mistaken payment; in pure unjust enrichment (Article 22) there need be no mistake — the acquisition at another’s expense lacks any legal ground altogether.

4. Quasi-contracts (Article 2142) form an open category. They are juridical relations arising from lawful, voluntary, and unilateral acts to prevent unjust enrichment. The Civil Code expressly names negotiorum gestio (unsolicited management of another’s affairs) and solutio indebiti, but as held in DACODECO, the enumeration is not exclusive. A quasi-contractual relation may be imposed wherever a benefit is conferred without a pre-existing contract, and no crime or quasi-delict is involved, to prevent unjust enrichment. Thus, accion in rem verso under Article 22 functions as the residual, subsidiary action for unjust enrichment cases that do not fall under any named quasi-contract or other cause of action.

5. Article 23 stands on a different footing: it imposes liability for indemnity even when the act causing property damage was not negligent or intentional, so long as the defendant was benefited. It is not identical to unjust enrichment — it deals with damage to property — but complements Article 22 by preventing a windfall from harmful but faultless acts.

Practically, counsel must first determine whether the facts support a specific cause of action (contract, quasi-delict, solutio indebiti, negotiorum gestio, or other named relationship). Only when no such remedy exists may accion in rem verso be invoked. A complaint should plead all four requisites explicitly, particularly the absence of any other remedy. Failure to do so is a ground for dismissal.

Recent Developments

The most recent Supreme Court pronouncement touching on unjust enrichment is Frian B. Lambo v. Evelyn Vega-Rose, G.R. No. 269085, 19 February 2026, which applied solutio indebiti but grounded its reasoning in the fundamental principle that no person should unjustly enrich themselves at another’s expense. No legislative amendments to Articles 22–23 or Title XVII of the Civil Code were identified.

Web research sources, notably Respicio’s bar review materials and Alburolaw’s commentary, consistently corroborate the database case holdings. The Respicio page on accion in rem verso (Web 1) and the Alburolaw article “What is Accion In Rem Verso?” (Web 32) www.alburolaw.com restate the four requisites and cite Land Bank of the Philippines v. Alfredo Ong, National Power Corporation v. Benguet Electric Cooperative, and the earlier Central Bank v. CA. The Respicio discussion of solutio indebiti distinctions (Web 8) explains the scope and mistake requirement. These sources reflect a stable, consistent doctrine.

Analysis

Applying the rules to the general legal inquiry, the following conclusions emerge:

• The definition of unjust enrichment is found in the conjunction of Article 22 and the judicial gloss in Loria v. Muñoz: it is the retention of a benefit (money or property) by a person without a valid basis, causing loss to another. The Court’s broad language — “against the fundamental principles of justice, equity and good conscience” — signals that the doctrine is an equitable safety valve.

• The requisites of accion in rem verso are four-fold: enrichment, loss, absence of just cause, and subsidiarity. Every element must be proved. The subsidiarity requirement is the most litigated; a plaintiff who fails to demonstrate that no other action lies will lose. This is because the Civil Code provides a hierarchy of obligations: contract, quasi-contract, crime, quasi-delict, and finally, the residual accion in rem verso. If a specific quasi-contract such as solutio indebiti fits, that is the mandatory remedy — the more general action is unavailable.

• Distinction from solutio indebiti: The core difference is the presence or absence of mistake. In solutio indebiti (Article 2154), the payor delivers something by mistake, believing it to be due. In pure unjust enrichment under Article 22, there is no such mistaken delivery; rather, the defendant acquires something at the plaintiff’s expense without any legal ground — for example, by retaining money received for a project that never materialized (Loria). Procedurally, solutio indebiti is not subsidiary; it stands on its own as a quasi-contract. If the payment was indeed made by mistake, the plaintiff must sue under Article 2154, not Article 22.

• Distinction from quasi-contracts generally: Quasi-contracts (Article 2142) are a recognized source of obligation. Accion in rem verso is the remedy for unjust enrichment where no specific quasi-contract applies. In other words, all quasi-contracts — negotiorum gestio, solutio indebiti, and the innominate quasi-contracts recognized in DACODECO — serve the same ultimate goal of preventing unjust enrichment. But Article 22 is the catch-all when the scenario does not fit any particular quasi-contractual figure. A party who can point to a lawful, voluntary, and unilateral act that conferred a benefit may invoke a quasi-contract without needing to reach Article 22, because the benefit itself creates the obligation by operation of law.

• The obligation to return under Article 22 is absolute once the conditions are met: the person who acquires something at another’s expense without just or legal ground must return it. Under Article 23, the obligation is to indemnify — even if the act causing damage was not faulty — if the defendant was benefited.

For practitioners, the strategic imperative is to diagnose the facts early: is there a contract? A tort? A mistaken payment? If yes, plead that specific cause of action. Only if none exists, and the defendant was enriched without any legal justification at the plaintiff’s correlative loss, should a complaint for accion in rem verso under Article 22 be filed. Plead all four requisites with particularity and anticipate a motion to dismiss based on the existence of another remedy.

Section III — Action Plan & Evidence Guide

Recommended Strategy: A practitioner must first conduct a thorough factual investigation to determine if any contractual, quasi-contractual (especially solutio indebiti), or tortious relationship exists between the parties. If the facts fall within a recognized quasi-contract, that specific remedy must be pursued. If no other remedy is available and the defendant retains money or property at the plaintiff’s expense without legal ground, pursue accion in rem verso under Article 22 as a subsidiary action. The complaint must expressly allege and prove all four elements, and the evidence must establish the absence of any alternative legal basis for the enrichment.

Action Steps:

1. Screen for alternative remedies — Review all communications, contracts, receipts, and payment records. If a payment was made erroneously (mistake of fact or law), proceed under solutio indebiti (Article 2154), which does not require proving subsidiarity. If services were rendered without a contract but were accepted and benefited the other party, consider a claim under Article 2142 (innominate quasi-contract) citing Republic v. DACODECO.
2. Draft complaint with all four requisites — Specifically allege: (a) defendant’s enrichment; (b) plaintiff’s corresponding impoverishment; (c) absence of just or legal ground for enrichment (no contract, no statutory right, no donation, etc.); (d) lack of any other available action under contract, quasi-contract, crime, or quasi-delict. Cite Article 22 and Loria v. Muñoz.
3. Assemble proof of enrichment and loss — Gather certified true copies of bank statements, receipts, acknowledgment vouchers, and any written admission of receipt. Link the defendant’s receipt of value directly to a loss suffered by the plaintiff (e.g., funds traceable from plaintiff’s account to defendant’s).
4. Anticipate and rebut subsidiarity attacks — Prepare a candid written statement or affidavit explaining why no contractual, quasi-contractual, or delictual remedy applies. If the defendant asserts the existence of a contract (even an illegal one), rely on Loria’s holding that prevention of unjust enrichment overrides in pari delicto when applicable.

Evidence Checklist:

• Receipts / acknowledgment vouchers signed by defendant — proves defendant’s receipt of money or property (enrichment), obtain from plaintiff’s records.
• Bank statements or transfer confirmations — shows outflow of funds from plaintiff to defendant, establishing impoverishment correlative to enrichment.
• Correspondence, demand letters — demonstrates defendant’s retention without justification and refusal to return; may establish absence of legal ground.
• Certification or affidavit of no existing contract or pending action — supports the element of subsidiarity.
• If relying on Article 23 (indemnity without fault): photographs, repair estimates, or appraisal reports of the damaged property, plus proof that the defendant derived a benefit from the act or event.

⚠️ This is AI-generated legal research for reference only. It does not constitute legal advice. Consult a licensed Philippine attorney before making important legal decisions.

References

Legislation & Regulatory Issuances

• Civil Code of the Philippines (Republic Act No. 386)

Case Law

• Carlos A. Loria v. Ludolfo P. Muñoz, Jr., G.R. No. 187240 (15 Oct 2014)
• Republic v. Davao Contractors Development Cooperative (DACODECO), G.R. No. 210029 (20 Nov 2017)
• Frian B. Lambo v. Evelyn Vega-Rose, G.R. No. 269085 (19 Feb 2026)
• Dometila M. Andres v. Manufacturers Hanover & Trust Corp., G.R. No. 82670 (15 Sep 1989)
• Sebastian Siga-an v. Alicia Villanueva, G.R. No. 173227 (20 Jan 2009)
• What is Accion In Rem Verso? — www.alburolaw.com