The Principle of Good Faith in International Law

1. Introduction

The Principle of Good Faith in International Law occupies a foundational yet persistently contested position within the international legal order. It is invoked across treaty law, dispute settlement, negotiations, and State responsibility, but rarely articulated with doctrinal precision. Courts, tribunals, and States rely on good faith to justify interpretive choices, assess conduct, and police strategic behaviour, while simultaneously expressing caution about its indeterminate nature. This tension—between indispensability and conceptual vagueness—explains why good faith remains both central and elusive in international legal reasoning.

Good faith is not a moral exhortation external to law. It is a legal principle with recognized normative force, embedded in the structure of international obligations and the logic of consent-based cooperation. Its legal pedigree is evident in multiple sources: Article 2(2) of the Charter of the United Nations, the law of treaties as codified in the Vienna Convention on the Law of Treaties, the jurisprudence of the International Court of Justice, and its classification as a general principle of law under Article 38(1)(c) of the ICJ Statute (UN Charter 1945; Vienna Convention on the Law of Treaties 1969; Statute of the International Court of Justice 1945). Across these contexts, good faith performs a specific juridical function: it sustains the reliability of commitments while constraining opportunistic conduct that formally complies with legal rules but undermines their purpose.

The analytical challenge addressed in this article is not to celebrate good faith as a universal solvent for legal hard cases, but to explain how it operates as a disciplined legal standard. Good faith does not create obligations independently of consent, nor does it authorise courts to rewrite treaties or impose equitable outcomes detached from positive law. Instead, it functions as a control principle. It shapes how obligations are performed, how treaties are interpreted, how negotiations are conducted, and how rights are exercised. Its role is corrective rather than creative. Where legal rules are vulnerable to manipulation through literalism, strategic silence, or procedural abuse, good faith supplies a normative boundary that preserves the integrity of the legal system without displacing its foundational structure.

This article adopts a doctrinal and practice-oriented approach to the Principle of Good Faith in International Law. It treats good faith as an objective standard of conduct rather than a subjective inquiry into intention, and it analyses its operation across distinct legal fields: treaty formation and performance, interpretation, unilateral acts, negotiations, estoppel and acquiescence, abuse of rights, and State responsibility. Particular attention is given to judicial technique, evidentiary thresholds, and the limits that international courts have imposed on their own use of the principle. By grounding the analysis in case law and institutional practice, the article aims to show how good faith functions in concrete legal reasoning rather than as an abstract ethical ideal.

The central claim developed throughout the article is that good faith is best understood as a systemic stabiliser. It protects the expectation that international commitments will be honoured as they were reasonably understood, while preventing States from exploiting formal legal categories to defeat substantive obligations. At the same time, its disciplined use is essential to legal certainty. When detached from identifiable rules and criteria, good faith risks degenerating into an empty rhetorical device. When properly anchored, it remains one of the most effective tools available to international law for reconciling consent, cooperation, and accountability.

2. Legal Status, Sources, and Systemic Role

2.1 Good Faith as a General Principle of Law

The most stable doctrinal foundation of the Principle of Good Faith in International Law lies in its classification as a general principle of law recognised by civilised nations under Article 38(1)(c) of the Statute of the International Court of Justice. This provision reflects a methodological choice made at the moment of the Court’s creation: international adjudication would not rely exclusively on treaties and custom, but could also draw upon fundamental legal principles common to domestic legal systems, transposed to the international plane where appropriate (ICJ Statute 1945).

The route from domestic law to international law is not mechanical. General principles are not transplanted wholesale, nor are they derived from any single legal tradition. Instead, they emerge through comparative convergence: where a principle is widely recognised across diverse legal systems as necessary to the functioning of law itself, international law may adopt it as a supplementary source. Good faith meets this criterion. It operates in civil law, common law, and mixed systems as a foundational requirement governing the performance of obligations, the exercise of rights, and the integrity of legal processes. Its internationalisation reflects functional necessity rather than moral aspiration.

The status of good faith as a general principle matters because it performs a specific legal task that treaties and custom cannot always perform. General principles serve primarily as gap-fillers and as tools of legal reasoning. Where no treaty rule exists, and where custom is underdetermined or fragmented, courts may rely on general principles to avoid non liquet and to preserve the coherence of the legal system. In addition, general principles support reasoning by analogy, allowing tribunals to articulate standards of conduct that are implicit in the structure of legal obligation even when not expressly codified.

It is essential to distinguish a general principle from a customary rule. Customary international law requires evidence of consistent State practice accompanied by opinio juris. The proof is empirical and inductive. By contrast, a general principle does not depend on demonstrating State practice in the international sphere. Its legitimacy flows from its recognition in domestic legal orders and its suitability for international application. As a result, the legal work performed by good faith as a general principle is different from that performed by good faith as a customary norm. It does not primarily regulate conduct directly; it structures interpretation, evaluation, and adjudication. This distinction explains why good faith is frequently invoked in judicial reasoning even when its content cannot be reduced to a specific rule of behaviour.

2.2 Good Faith as a Charter Principle of Inter-State Conduct

Beyond its status as a general principle, good faith is expressly embedded in the constitutional framework of the international legal order through Article 2(2) of the Charter of the United Nations. That provision requires Members to fulfil their Charter obligations in good faith. The inclusion of good faith at this foundational level signals that compliance with international obligations is not exhausted by formal adherence to their wording; it also entails loyalty to their purpose and integrity (UN Charter 1945).

Article 2(2) establishes a baseline behavioural requirement applicable to all Charter obligations. It reinforces the expectation that States will not seek to evade their commitments through manipulation, strategic delay, or purely formal compliance that defeats substantive objectives. In this role, good faith functions as a systemic norm that underpins cooperation within the United Nations framework, particularly in areas such as the peaceful settlement of disputes, collective security, and cooperation with UN organs.

At the same time, the Charter formulation of good faith has clear limits. It does not operate as a free-standing source of obligations independent of the Charter’s substantive provisions. Nor does it authorise States or courts to override specific Charter rules on the basis of perceived fairness or equity. Article 2(2) presupposes the existence of an obligation and regulates how that obligation is performed. It cannot be invoked to expand jurisdiction, justify unilateral measures contrary to explicit Charter constraints, or displace carefully negotiated institutional balances. Its role is supportive and interpretive, not creative.

2.3 Good Faith as a Treaty-Law Requirement

The most detailed codification of the Principle of Good Faith in International Law appears in the Vienna Convention on the Law of Treaties. The Convention incorporates good faith at three structurally distinct points, each corresponding to a different phase of the treaty lifecycle.

First, Article 26 affirms that treaties in force are binding upon the parties and must be performed in good faith. This formulation links pacta sunt servanda directly to good faith, making clear that treaty compliance is not limited to literal execution but extends to honest and reasonable performance consistent with the agreement’s object and purpose.

Second, Article 31 places good faith at the centre of treaty interpretation. Treaties must be interpreted in good faith in accordance with the ordinary meaning of their terms, read in context and in light of their object and purpose. Here, good faith operates as an interpretive discipline. It constrains both hyper-literal readings that strip provisions of practical effect and overly teleological readings that impose obligations not grounded in the text.

Third, Article 18 imposes a good-faith obligation at the pre-entry stage. States that have signed a treaty or otherwise expressed consent subject to ratification must refrain from acts that would defeat the object and purpose of the treaty. This obligation protects reliance and preserves the integrity of the negotiating process without imposing a duty to ratify.

The Vienna Convention’s treatment of good faith reflects a broader logic of codification combined with continuity of custom. The Convention did not invent good faith; it systematised and clarified existing international practice. As a result, good faith operates both within and beyond the Convention framework. It applies to treaties concluded before the Convention’s entry into force, to treaties involving non-parties in relevant respects, and to treaty-like instruments not formally governed by the Convention. Its authority does not depend exclusively on the Convention, but the Convention provides its most coherent doctrinal expression.

2.4 Good Faith in Judicial Method

International courts and tribunals employ good faith as a control concept within legal reasoning rather than as an autonomous source of decision. Its methodological role is to stabilise interpretation and application by disciplining two opposing risks.

On one side, good faith constrains excessive formalism. Literal readings of legal texts can sometimes enable evasion of obligations through technical compliance that undermines agreed purposes. In such cases, good faith allows courts to reject interpretations that are textually plausible but normatively destructive of the bargain the parties struck.

On the other side, good faith constrains unbounded teleology. Appeals to object and purpose, effectiveness, or equity can tempt adjudicators to move beyond interpretation into revision. Good faith operates here as a brake, reminding courts that consent remains the foundation of international obligation and that interpretive creativity must remain anchored to the text and context of the instrument.

Used in this disciplined way, the Principle of Good Faith in International Law enhances legal certainty rather than undermining it. It does not replace rules with discretion; it ensures that rules are applied in a manner consistent with their function within a cooperative legal order.

3. Concept and Architecture of the Principle

3.1 State of Mind vs Standard of Behaviour

A persistent source of confusion surrounding the Principle of Good Faith in International Law lies in the failure to distinguish clearly between good faith as a state of mind and good faith as a standard of behaviour. In its subjective sense, good faith refers to the absence of deceit, bad intention, or deliberate dishonesty. This conception focuses on what a State believed or intended at the time of acting. While such an understanding has relevance in limited contexts—such as questions of knowledge or intent in attribution—it has never provided a workable foundation for general international legal obligations.

International law has progressively moved away from subjective good faith toward an objective standard of conduct. Objective good faith assesses behaviour against externally verifiable criteria: fairness, consistency, honesty in representations, and reasonableness in the exercise of rights. The decisive question is not what a State claims to have believed, but how its conduct would reasonably be understood by other actors operating within the same legal framework. This shift reflects structural realities. States are collective actors, intentions are difficult to prove, and international adjudication cannot depend on speculative inquiries into internal decision-making processes (Kolb 2017).

Judicial practice confirms this trend. International courts rarely inquire into the psychological motivations of States. Instead, they examine outward conduct, patterns of behaviour, and the legal effects produced by representations and omissions. Good faith is thus treated as an objective legal standard that governs how rights are exercised and obligations performed. This approach preserves legal certainty while preventing strategic invocations of sincerity to shield conduct that undermines cooperative commitments (Bin Cheng 1953).

3.2 Core Content Elements

Although good faith resists exhaustive definition, international practice reveals a consistent minimum content that gives the principle operational meaning. This minimum content does not replicate the full doctrinal richness of good faith in domestic private law, nor does it impose broad duties of cooperation absent a legal basis. Instead, it establishes a limited set of behavioural expectations that are necessary for the stability of international legal relations.

The first element is consistency. States are expected to act coherently over time in relation to their legal positions. Abrupt reversals, contradictory claims, or selective invocation of rules may indicate bad faith when they undermine reasonable reliance or distort agreed frameworks. Consistency does not prohibit legal change, but it requires that change be articulated openly and prospectively.

The second element is transparency in representations. When States make statements, assurances, or formal positions, particularly in diplomatic or legal settings, good faith requires that such representations not be misleading. Silence, ambiguity, or strategic understatement may engage the principle when they induce reliance by other actors. This element is central to doctrines such as estoppel and unilateral acts (McNair 1961).

The third element is reasonableness in the exercise of rights. International law recognises that legal rights are not unlimited licences. Good faith constrains their exercise by excluding conduct that is formally lawful but manifestly disproportionate, opportunistic, or detached from the purpose for which the right exists. This reasonableness requirement operates without importing general notions of equity or fairness as autonomous sources of obligation.

The fourth element is respect for legitimate reliance. Where one State has reasonably relied on the conduct or representations of another, good faith may protect that reliance against sudden repudiation. This protection does not create obligations out of mere expectation, but it prevents States from benefiting from conduct that has induced reliance and then disavowing its legal consequences (Fitzmaurice 1957).

Together, these elements form a restrained and usable architecture of good faith. They avoid transforming the principle into an all-purpose corrective while ensuring that it performs its stabilising function within the international legal system.

3.3 Functions of Good Faith

(i) Integrity of Commitments

The primary function of the Principle of Good Faith in International Law is to safeguard the integrity of legal commitments. International obligations depend on trust that undertakings will be honoured not only formally but substantively. Good faith reinforces pacta sunt servanda by ensuring that compliance does not become an exercise in technical avoidance. It protects the expectation that agreed obligations will be performed in a manner consistent with their intended legal effect, thereby sustaining cooperation in a decentralised legal order (Oppenheim 1992).

(ii) Interpretive Discipline

Good faith plays a central role in treaty interpretation by disciplining interpretive choices. It anchors interpretation in the text, context, and object and purpose of an agreement, while excluding readings that are opportunistic or self-serving. This function is particularly important where treaty language admits more than one plausible meaning. Good faith guides interpreters toward readings that preserve the balance of rights and obligations reflected in the agreement, without authorising judicial rewriting of negotiated terms (Gardiner 2015).

(iii) Procedural Integrity

A further function of good faith concerns procedural integrity. In negotiations, dispute settlement, and compliance processes, good faith requires meaningful engagement rather than formal participation devoid of substance. Procedural bad faith may take the form of deliberate delay, refusal to consider proposals, inconsistent procedural positions, or abuse of jurisdictional mechanisms. By policing such conduct, good faith preserves the effectiveness of legal processes without imposing outcomes on unwilling parties (Villiger 2009).

(iv) Corrective Boundary-Setting

Finally, good faith operates as a corrective boundary-setting principle. It underpins doctrines such as abuse of rights, estoppel, and acquiescence, all of which prevent States from exploiting formal legal positions in ways that undermine stability and reliance. This corrective function is applied cautiously. International tribunals impose a high evidentiary threshold before invoking it, precisely to avoid substituting discretion for law. When applied, it does not negate rights but restricts their exercise at the point where legality becomes manipulation.

Through these interconnected functions, the Principle of Good Faith in International Law operates as a structural stabiliser rather than a source of substantive innovation. It ensures that international law remains workable in practice while remaining anchored to consent and legal certainty.

4. Good Faith in the Law of Treaties

4.1 Formation-Stage Duties and Reliance Protection

4.1.1 Article 18 VCLT and the “Do Not Defeat Object and Purpose” Obligation

Article 18 of the Vienna Convention on the Law of Treaties gives concrete legal expression to good faith at the pre-entry stage of treaty relations. Once a State has signed a treaty subject to ratification, or has otherwise expressed consent to be bound pending entry into force, it is obliged to refrain from acts that would defeat the object and purpose of the treaty. The legal rationale of this obligation is frequently misunderstood. Signature does not create a duty to ratify, nor does it provisionally bind the State to all treaty obligations. Instead, it generates a reliance-based restraint grounded in good faith (Vienna Convention on the Law of Treaties 1969).

The restraint arises because the signature signals a serious intention to consider becoming bound. Other negotiating States are entitled to rely, within limits, on that signal when adjusting their conduct. Good faith protects this reliance by preventing the signatory from deliberately undermining the treaty while keeping the formal option of ratification open. The obligation is therefore negative and temporary: it restrains destructive conduct but preserves sovereign freedom of final consent (Aust 2013).

The threshold for conduct that “defeats the object and purpose” is intentionally high. It is not triggered by ordinary policy divergence, preparatory measures, or even inconsistent domestic legislation adopted before ratification. Defeating the object and purpose requires conduct that strikes at the core of the treaty’s essential aims, making its future performance meaningless or radically impaired. Examples include dismantling a regulatory regime that the treaty seeks to establish, transferring protected assets in a way that frustrates treaty guarantees, or undertaking irreversible acts incompatible with the treaty’s central obligations (McNair 1961).

This high threshold reflects a balance inherent in good faith. Too low a standard would transform Article 18 into a de facto obligation to comply without consent. Too high a standard would empty the provision of legal effect. International practice resolves this tension by confining Article 18 to clear cases of bad-faith pre-emption, thereby preserving both reliance protection and State autonomy.

4.1.2 Pactum de Contrahendo and the Limits of a “Duty to Conclude”

International law occasionally recognises obligations to negotiate, often described as pactum de contrahendo. These obligations arise from treaties, unilateral undertakings, or judicial decisions, and they are governed by the Principle of Good Faith in International Law. A critical doctrinal limit, however, is that a duty to negotiate does not automatically entail a duty to agree.

Good faith requires that negotiations be conducted genuinely. This entails willingness to engage, openness to persuasion, and reasoned consideration of proposals. It excludes conduct aimed solely at delay, obstruction, or the creation of a façade of compliance. Strategic stalling, refusal to articulate positions, or insistence on conditions that negate the negotiation’s purpose may indicate a lack of good faith (Kolb 2017).

At the same time, good faith does not compel a State to sacrifice core interests or accept outcomes it finds unacceptable. The duty concerns process, not result. This distinction is essential to preserving consent as the foundation of treaty obligations. Good faith separates genuine engagement from bad-faith simulation, but it does not transform negotiations into adjudication by another name. The line is crossed only where a State uses negotiations instrumentally to avoid existing obligations or to block agreed dispute-settlement pathways.

4.2 Performance-Stage Duties

4.2.1 Article 26 VCLT and Pacta Sunt Servanda as a Good-Faith Rule

Article 26 of the Vienna Convention affirms that treaties in force are binding upon the parties and must be performed in good faith. This provision integrates good faith directly into the core of treaty obligation. Performance is not exhausted by mechanical compliance with textual requirements; it also excludes manipulative compliance through form.

Good faith constrains behaviour that adheres to the letter of a treaty while undermining its substance. Examples include exploiting drafting ambiguities to avoid burdens clearly contemplated by the parties, sequencing actions to technically comply while neutralising practical effect, or invoking procedural rights to block performance indefinitely. Such conduct may remain formally lawful, yet violate the good-faith requirement embedded in pacta sunt servanda (Villiger 2009).

This understanding preserves the normative force of treaties in a decentralised system. Without good faith, treaty obligations would be vulnerable to systematic erosion through legal engineering. With good faith, performance is assessed against the reasonable expectations generated by the agreement, without introducing open-ended fairness review.

4.2.2 Material Breach, Reciprocity, and Opportunistic Termination

The law of termination and suspension illustrates how good faith constrains the invocation of treaty remedies. The Vienna Convention permits termination or suspension in response to material breach, reflecting reciprocity as a structural feature of treaty relations. Good faith operates as a filter in this context.

First, it prevents pretextual reliance on minor or technical breaches to justify termination. Not every deviation constitutes a material breach. Good faith requires an assessment of gravity, impact on the treaty’s object and purpose, and the proportionality of the response. Second, it preserves the right to respond decisively to serious non-performance. Good faith does not impose tolerance of fundamental violations, nor does it require continued performance in the face of persistent repudiation (Gardiner 2015).

In this way, good faith stabilises reciprocity. It prevents opportunistic exit while maintaining the credibility of enforcement mechanisms.

4.2.3 Change of Circumstances and Impossibility

Good faith also shapes the application of Articles 61 and 62 of the Vienna Convention, which govern impossibility of performance and fundamental change of circumstances. Both doctrines are exceptional, reflecting the priority of stability in treaty relations.

Good faith reinforces the restrictive interpretation of these provisions. Claims of impossibility or fundamental change must not be self-induced, selectively invoked, or framed opportunistically. The pleading State bears a heavy burden to demonstrate that the change was unforeseen, fundamental, and radically transformed the extent of obligations. Even where the threshold is met, good faith supports cooperative adjustment rather than immediate disengagement, where adjustment remains feasible (Fitzmaurice 1957).

Thus, good faith functions as a safeguard against opportunistic invocation of exceptional doctrines while preserving their availability in genuinely extraordinary situations.

4.3 Interpretation-Stage Duties

4.3.1 Article 31 VCLT: Good Faith as an Interpretive Constraint

Article 31 of the Vienna Convention places good faith at the heart of treaty interpretation. Interpretation proceeds through an ordered sequence: ordinary meaning of the terms, read in context, and in light of the treaty’s object and purpose. Good faith is not an additional step, but the discipline governing the entire process.

It prevents interpreters from “reading in” obligations that lack textual grounding, as well as from “emptying out” agreed provisions through excessively narrow readings. Good faith ensures that interpretation respects both the semantic content of the text and the balance of interests reflected in the agreement, maintaining fidelity to consent (Gardiner 2015).

4.3.2 Subsequent Practice and Conduct

Subsequent practice can play an important role in interpretation, but good faith distinguishes between genuine common understanding and unilateral self-serving behaviour. Practice qualifies as interpretive only where it reflects concordant conduct of the parties establishing an agreement regarding interpretation. Isolated or contested practice does not meet this standard.

The good-faith rationale for privileging convergent practice lies in reliance and mutuality. Where parties act consistently over time, they generate shared expectations that interpretation should respect. Unilateral reinterpretation, by contrast, risks transforming practice into a tool of legal revision rather than clarification (Kolb 2017).

4.3.3 Effectiveness and Judicial Restraint

The principle of effectiveness, often expressed as ut res magis valeat quam pereat, is frequently associated with good-faith interpretation. Properly understood, it is a technique, not an independent rule. Good faith supports effectiveness only within the boundaries of text and consent.

Effectiveness cannot justify interpretations that impose obligations never accepted or that alter negotiated compromises. Good faith thus operates as a limit on judicial creativity. It supports interpretations that give practical meaning to treaty provisions, while blocking revisionism disguised as purposive reasoning. In this restrained form, effectiveness enhances, rather than undermines, the authority of treaty law.

Through these formation, performance, and interpretation-stage duties, the Principle of Good Faith in International Law emerges as a structural element of treaty relations, ensuring reliability, coherence, and restraint without displacing the centrality of consent.

5. Good Faith and Unilateral Acts of States

5.1 Binding Unilateral Declarations and Reliance

The Principle of Good Faith in International Law plays a decisive role in determining when unilateral acts of States acquire binding legal effect. Unlike treaties, unilateral declarations do not arise from reciprocal consent. Their normative force rests instead on the protection of reliance and the stability of international relations. The jurisprudence of the International Court of Justice, most notably in the Nuclear Tests cases, provides the clearest articulation of this logic (International Court of Justice 1974).

In Nuclear Tests, the Court held that public declarations made by French authorities concerning the cessation of atmospheric nuclear testing were legally binding. The Court did not ground this conclusion in consent by other States, but in good faith. France had made clear, public, and authoritative statements indicating a commitment to terminate a specific course of conduct. Other States were entitled to rely on those assurances. Good faith required that such reliance not be disappointed through subsequent reversal.

The doctrinal significance of this reasoning lies in its emphasis on objective conduct rather than subjective intent. The Court focused on the outward form, publicity, and specificity of the declarations, as well as their context. Where a State deliberately communicates an undertaking to the international community, and that undertaking is capable of producing reliance, good faith supports treating the declaration as legally binding. This approach protects trust in international cooperation by ensuring that States cannot benefit from the political advantages of public commitments while avoiding their legal consequences (McNair 1961).

Good faith thus operates as the bridge between unilateral expression and legal obligation. It does not suggest that every statement has binding force. Rather, it identifies a narrow category of declarations where the combination of clarity, authority, and reliance justifies legal effect. In this way, good faith reinforces predictability without undermining the consensual structure of international law.

5.2 Limits: Ambiguity, Authority, and Revocation

The recognition of binding unilateral declarations is accompanied by strict doctrinal limits. These limits are essential to prevent good faith from becoming a mechanism for generating obligations through ambiguity or informal political rhetoric.

The first guardrail is clarity of intent. For a unilateral declaration to be binding, it must express an intention to be legally bound, assessed objectively. Vague political statements, aspirational language, or expressions of future policy preference do not suffice. Ambiguity operates against binding force. Where the content or legal character of a declaration is unclear, good faith does not transform it into an obligation (Aust 2013).

The second guardrail concerns attributable authority. Only statements made by organs or officials competent to represent the State internationally can generate binding effects. This requirement preserves institutional responsibility and prevents inadvertent obligation through unauthorised conduct. Good faith protects reliance only where reliance itself is reasonable, and reasonableness depends on the apparent authority of the speaker (Oppenheim 1992).

The third guardrail relates to revocation and modification. Unilateral declarations are not necessarily irrevocable. Good faith does not prohibit withdrawal in all circumstances. However, revocation is constrained where other States have already relied on the declaration. The decisive factor is not the unilateral will of the declaring State, but the legal consequences of reliance already generated. Where reliance is concrete and reasonable, abrupt withdrawal may itself constitute a breach of good faith (Kolb 2017).

Finally, the burden of proof rests on the party invoking the binding nature of a unilateral act. That party must establish the existence of a clear commitment, attributable authority, and circumstances capable of giving rise to reliance. Good faith does not reverse evidentiary standards. It operates within them, ensuring that the binding force is recognised only where legal certainty is genuinely served.

These limits illustrate the disciplined function of good faith in the law of unilateral acts. The principle does not expand the sources of international law indiscriminately. It protects trust where States have chosen to generate it, while preserving space for political expression and diplomatic flexibility. In this calibrated role, the Principle of Good Faith in International Law strengthens cooperation without eroding the foundational requirement of legal certainty.

6. Good Faith in Negotiations and Dispute Settlement

6.1 The Duty to Negotiate in Good Faith

The Principle of Good Faith in International Law gives concrete legal meaning to obligations to negotiate. Such obligations arise from treaties, unilateral undertakings, and judicial decisions, and they are increasingly common in fields such as boundary delimitation, environmental cooperation, and dispute settlement. While international law does not impose a general duty to negotiate, once such a duty exists, good faith governs its performance.

Good faith negotiations are not assessed by reference to outcomes, but by reference to conduct. International practice has crystallised a set of assessable indicia that distinguish genuine engagement from procedural simulation. First, meaningful engagement requires participation that goes beyond formal attendance. Parties must articulate positions, respond to proposals, and demonstrate openness to discussion. Silence or repetitive restatement of fixed positions may signal a lack of good faith when it renders negotiations ineffective.

Second, reasoned consideration of proposals is essential. Good faith does not require acceptance of counterproposals, but it does require that they be examined and addressed on their merits. Blanket rejection without explanation, or the refusal to engage with the substance of proposals, undermines the negotiating process and may indicate strategic obstruction (Villiger 2009).

Third, absence of unjustified delay is a recurring criterion. Delays may be legitimate where complex technical issues are involved, but unexplained postponements, repeated requests for extensions without progress, or procedural cycling designed to exhaust the other party may breach the duty of good faith. Time, in this context, becomes a substantive element of conduct.

Finally, good faith excludes procedural sabotage. This includes introducing extraneous conditions that negate the object of negotiations, shifting procedural frameworks mid-process, or linking negotiations to unrelated demands. These behaviours do not violate a duty to agree, but they undermine the integrity of a duty to negotiate (Kolb 2017).

Through these indicia, good faith transforms an abstract obligation into a legally assessable standard without eroding State autonomy over substantive outcomes.

6.2 Court-Ordered Negotiations and Compliance Architecture

International courts have increasingly relied on negotiated solutions as part of their remedial architecture. In such contexts, good faith acquires a distinctive function. Rather than resolving all aspects of a dispute, courts may declare rights and obligations while directing the parties to negotiate outstanding issues in good faith.

The Gabčíkovo–Nagymaros Project case illustrates this approach. After finding that both Hungary and Slovakia had acted unlawfully in different respects, the International Court of Justice emphasised the continuing validity of the treaty relationship and instructed the parties to negotiate in good faith to adapt the treaty’s implementation to changed circumstances (International Court of Justice 1997).

Good faith added substance to this remedial structure in several ways. It framed negotiations as a continuation of legal obligation rather than a purely political exercise. It required the parties to take the Court’s findings seriously as legal parameters within which negotiations had to occur. It also excluded unilateral implementation strategies that would have entrenched one party’s advantage while negotiations were pending.

Importantly, the Court did not prescribe specific outcomes. Good faith did not empower the Court to impose a revised treaty or dictate technical solutions. Instead, it functioned as a compliance mechanism that preserved flexibility while ensuring that negotiations were not used to neutralise judicial authority. This illustrates how the Principle of Good Faith in International Law supports the effectiveness of adjudication without collapsing the distinction between judicial settlement and diplomatic resolution (Gardiner 2015).

6.3 Abuse of Process and Procedural Good Faith

Procedural good faith operates as a constraint on how States conduct themselves before international courts and tribunals. Abuse of process is not defined exhaustively, but international jurisprudence has identified recurring patterns of conduct incompatible with good faith.

One such pattern is inconsistent pleadings. States may not adopt mutually contradictory legal positions across different stages of the same proceedings, or across related proceedings, when doing so undermines procedural integrity. While legal argumentation permits alternative submissions, strategic inconsistency designed to secure advantage at different procedural moments may constitute abuse.

A second pattern involves tactical jurisdictional manoeuvres. This includes initiating parallel proceedings to fragment disputes, raising jurisdictional objections belatedly after substantive engagement, or manipulating procedural rules to delay adjudication. Good faith requires that jurisdictional arguments be advanced coherently and at appropriate stages (Shaw 2017).

A third category concerns the concealment of decisive facts. Procedural good faith obliges parties to present their case honestly. Withholding information that is central to the dispute, particularly where disclosure is required by procedural rules or judicial orders, undermines the integrity of adjudication and may attract adverse inferences.

Finally, tribunals have treated attempts to re-litigate settled points under new labels as incompatible with good faith. Once a matter has been conclusively decided, procedural economy and legal certainty require respect for res judicata. Reframing identical claims or arguments as distinct disputes does not reset the legal process.

In all these contexts, the role of good faith is corrective rather than punitive. Tribunals apply it cautiously, mindful of the need to preserve access to justice and legitimate advocacy. When applied, it protects the procedural framework that allows international adjudication to function as a credible mechanism for dispute settlement.

7. Estoppel, Acquiescence, Waiver, and Legitimate Reliance

7.1 Estoppel as a Good-Faith Doctrine

Estoppel occupies a distinctive position in the architecture of the Principle of Good Faith in International Law. It is not a primary source of obligation, nor does it generate rights independently of existing legal relationships. Instead, it operates as a reliance-based corrective that precludes a State from contradicting a position it has previously adopted when another State has reasonably relied on that position to its detriment.

The legal logic of estoppel is grounded in good faith rather than reciprocity. Its function is to protect the integrity of representations and the stability of legal relations. Where a State, through words, conduct, or a combination of both, induces another State to adopt a course of action or to refrain from acting, good faith requires consistency. The representing State may be barred from later asserting a contradictory legal position if doing so would unfairly prejudice the relying State (Bin Cheng 1953).

International tribunals have treated estoppel with caution. Its application requires a high evidentiary threshold. Three core elements are typically examined. First, there must be a clear and unambiguous representation attributable to the State. Second, the other State must have relied on that representation in a manner that was reasonable in the circumstances. Third, the relying State must have suffered prejudice or altered its position as a consequence of that reliance. Absent these elements, estoppel does not arise.

Good faith is the normative glue that holds these elements together. It explains why legal consistency is required even in the absence of a treaty obligation, and why not every inconsistency gives rise to preclusion. Estoppel does not punish legal error or evolution of policy. It intervenes only where an inconsistency would undermine reliance that international law considers worthy of protection. In this restrained form, estoppel reinforces trust without freezing States permanently into past positions (Kolb 2017).

7.2 Acquiescence and Silence

Acquiescence is closely related to estoppel but operates through omission rather than express representation. It concerns situations where a State’s silence or inaction is treated as legally meaningful, indicating acceptance of a situation or claim asserted by another State. Because silence is inherently ambiguous, international law approaches acquiescence with particular caution.

The Principle of Good Faith in International Law provides the framework for determining when silence may carry legal consequences. Silence is not consent by default. It becomes legally relevant only under strict conditions: the circumstances must call for a reaction; the State must have knowledge, or be reasonably expected to have knowledge, of the relevant facts or claims; and the silence must persist over a sufficient period to justify reliance (Shaw 2017).

The law’s caution reflects a structural concern. Treating silence too readily as acquiescence would enable manufactured consent and destabilise legal relations. States may remain silent for political, strategic, or practical reasons unrelated to acceptance. Good faith grounds a narrow test that balances stability against voluntarism. It protects reliance only where silence reasonably conveys acceptance and where reliance on that silence would itself be consistent with honest dealing.

Acquiescence thus functions as a limited doctrine of reliance protection. It does not create obligations through passivity alone. It prevents States from exploiting prolonged silence to later contest situations they effectively allowed to solidify. In this way, good faith ensures that stability is preserved without transforming inaction into an open-ended source of obligation (McNair 1961).

7.3 Boundary and Territorial Contexts

Boundary and territorial disputes provide the clearest illustrations of estoppel and acquiescence grounded in good faith. These contexts heighten the importance of stability, reliance, and predictability. Once territorial arrangements crystallise, disruption carries significant political and practical consequences.

The Temple of Preah Vihear case remains the paradigmatic example. The International Court of Justice placed decisive weight on Thailand’s prolonged acceptance of a map indicating the location of the boundary, despite later contestation. The Court did not treat the map as binding in itself. Instead, it emphasised Thailand’s conduct over time, its failure to object when circumstances clearly called for reaction, and Cambodia’s reliance on that conduct in administering the territory (International Court of Justice 1962).

From this and similar cases, tribunals have identified recurring criteria. Clarity of the initial representation or situation is essential; ambiguous acts cannot ground reliance. Time matters, as acquiescence requires a sustained period of inaction. Knowledge is critical; silence cannot be legally meaningful where a State was unaware, or could not reasonably have been aware, of the relevant claim. Finally, stability interests weigh heavily in territorial contexts, reinforcing the good-faith rationale for protecting settled expectations.

These cases demonstrate the disciplined role of good faith. Estoppel and acquiescence do not function as shortcuts to sovereignty or as substitutes for title. They operate as stabilising doctrines that prevent disruptive reversals once reliance has solidified. By grounding these doctrines in good faith, international law protects both fairness in inter-State dealings and the practical need for durable territorial arrangements.

In sum, estoppel, acquiescence, waiver, and legitimate reliance illustrate how the Principle of Good Faith in International Law operates at the margins of formal obligation. It does not create rights through equity alone, but it ensures that States cannot profit from inconsistency, silence, or strategic reversal when such conduct would undermine trust and stability in the international legal order.

8. Abuse of Rights and the Policing of Opportunism

8.1 Doctrinal Status and Evidentiary Threshold

Abuse of rights represents one of the most restrained applications of the Principle of Good Faith in International Law. It is not an autonomous ground of illegality, nor does it negate the existence of a legal right. Instead, it operates as a control concept that limits the manner in which a right may be exercised. Its doctrinal status is deliberately narrow, reflecting the centrality of consent and legal certainty in the international legal order.

International tribunals have consistently treated abuse of rights as a high bar doctrine. A finding of abuse requires more than the existence of adverse effects on another State. It demands clear evidence that a right, though formally valid, has been exercised in a manner incompatible with its function or purpose. This evidentiary threshold explains why tribunals are reluctant to invoke abuse of rights absent compelling circumstances. Overuse of the doctrine would risk transforming good faith into a vehicle for discretionary equity, undermining predictability and stability (Kolb 2017).

The cautious approach serves an important systemic function. International law relies on clearly defined rights and obligations to structure expectations. If every exercise of a right producing negative consequences could be challenged as abusive, legal certainty would erode. States would be unable to rely on their entitlements, and adjudication would drift toward subjective assessments of fairness. By requiring demonstrable misuse rather than mere inconvenience or imbalance, the law preserves the integrity of rights while retaining a corrective tool for exceptional cases (Bin Cheng 1953).

Good faith provides the normative justification for this restraint. It explains why abuse of rights exists at all—because legal rights are not licences for manipulation—while simultaneously justifying its limited application. Abuse of rights is not a shortcut to rebalancing interests; it is a safeguard against opportunism that threatens the coherence of legal commitments.

8.2 Typical Abuse Patterns

Although tribunals avoid rigid categorisation, international practice reveals recurring patterns of conduct that may indicate abuse of rights when supported by sufficient evidence. These patterns do not constitute independent rules, but analytical indicators assessed through the lens of good faith.

One category involves exercising a right for an extraneous purpose. A right may be abused where it is invoked not to realise its legitimate function, but to achieve an unrelated objective, such as economic pressure, political leverage, or circumvention of other obligations. The focus is not on motive in the psychological sense, but on the objective mismatch between the right’s function and the outcome pursued.

A second category concerns disproportionate harm to others. While international law does not impose a general proportionality requirement on all rights, extreme or manifestly excessive harm caused by the exercise of a right may indicate abuse when it is unnecessary to achieve the right’s legitimate aim. Good faith excludes the use of rights as instruments of gratuitous injury.

A third pattern involves strategic sequencing to defeat obligations. This occurs where a State structures the timing or order of lawful acts so as to neutralise existing or emerging obligations. Although each act may be lawful in isolation, their orchestration may reveal an intent to undermine the legal framework as a whole. In such cases, good faith allows tribunals to assess conduct holistically rather than atomistically (McNair 1961).

A fourth category is formal compliance with substantive evasion. This pattern mirrors concerns addressed in treaty performance. A State may comply meticulously with procedural requirements while ensuring that the substantive objectives of an obligation are frustrated. Where such behaviour is systematic and deliberate, it may cross the threshold into abuse.

These categories illustrate how the Principle of Good Faith in International Law polices opportunism without displacing legal rights. Abuse of rights remains exceptional, fact-intensive, and tightly constrained. Its value lies not in frequent application, but in its deterrent function. By signalling that extreme manipulation will not be shielded by formal legality alone, the doctrine reinforces confidence that international law cannot be reduced to a game of technical avoidance.

9. Good Faith and State Responsibility

9.1 Good Faith and the Structure of Secondary Rules

Within the law of State responsibility, the Principle of Good Faith in International Law does not operate as an independent rule of attribution or breach. Its role is structural and background-oriented. It shapes how the secondary rules codified in the Articles on Responsibility of States for Internationally Wrongful Acts (ARSIWA) are interpreted, invoked, and applied. In this sense, good faith supports the functioning of responsibility without altering its basic architecture (International Law Commission 2001).

Good faith influences, first, the invocation of responsibility. While ARSIWA does not impose an explicit good-faith requirement for invocation, international practice assumes that claims of responsibility must be advanced honestly, coherently, and without procedural manipulation. Invocation in bad faith—such as selective reliance on responsibility while tolerating identical conduct by allies, or the strategic inflation of minor breaches to justify escalation—risks undermining the credibility of the responsibility regime itself (Crawford 2013).

Second, good faith shapes the regime of countermeasures. Countermeasures are exceptional responses that suspend compliance with obligations in order to induce cessation and reparation. Their legality depends on purpose and proportionality. Good faith informs both elements. Countermeasures must be directed toward inducing compliance, not punishment or retaliation. They must also remain proportionate to the injury suffered and the seriousness of the breach. Good faith prevents States from disguising coercive or punitive measures as lawful countermeasures while preserving the remedial logic of reciprocity (Olleson 2015).

Third, good faith informs the obligation of cooperation in cessation and reparation. ARSIWA emphasises that responsible States must cease the wrongful act and make full reparation, while injured States must engage constructively in processes aimed at resolving the consequences of the breach. Good faith here excludes obstruction, strategic delay, or refusal to engage with reasonable modalities of reparation. It does not require agreement on outcomes, but it does require sincerity in compliance-oriented engagement (Crawford 2013).

In all these areas, good faith operates as an internal stabiliser. It does not expand responsibility or create new remedies. It ensures that the secondary rules function as mechanisms of accountability rather than instruments of opportunism.

9.2 Countermeasures and “Clean Hands” Arguments

The interaction between good faith and countermeasures has generated recurrent controversy, particularly through so-called “clean hands” arguments. States facing allegations of wrongful conduct have sometimes argued that an injured State’s lack of good faith, prior misconduct, or procedural impropriety should bar reliance on countermeasures or even responsibility claims altogether.

International law draws a careful distinction here. Legitimate good-faith constraints on countermeasures are well established. Countermeasures must be temporary, reversible where possible, and lifted once compliance is achieved. They must respect peremptory norms and fundamental humanitarian obligations. They must also be preceded by notice and an opportunity to negotiate unless urgency justifies immediate action. These constraints reflect good faith as a condition of lawful enforcement rather than as an equitable balancing device (International Law Commission 2001).

By contrast, improper “equitable vetoes” are rejected. Good faith does not authorise a responsible State to evade accountability by pointing to alleged imperfections in the injured State’s conduct. Nor does it permit tribunals to deny responsibility for serious breaches on the basis of abstract fairness or mutual fault. Such uses of good faith would undermine the integrity of the responsibility regime by reintroducing discretionary equity where the law has deliberately chosen rule-based accountability (Shaw 2017).

This distinction is especially important in cases involving serious breaches of international obligations. Allowing clean-hands arguments to block countermeasures or responsibility claims would reward wrongdoing and destabilise enforcement. Good faith, properly understood, constrains how countermeasures are used, not whether responsibility exists. It ensures proportionality and purpose while preserving the core principle that wrongful acts entail legal consequences.

In sum, the Principle of Good Faith in International Law operates within State responsibility as a discipline of conduct, not a defence against accountability. It supports the effectiveness of ARSIWA by ensuring that responsibility mechanisms are used to restore legality rather than to escalate disputes or entrench inequity.

10. Selected Contexts Where Good Faith Does Distinct Work

10.1 International Investment Law

International investment law provides a dense laboratory for observing how the Principle of Good Faith in International Law operates within a specialised regime. Good faith arguments appear most prominently through treaty-based standards such as fair and equitable treatment (FET), protection of legitimate expectations, and procedural fairness. At the same time, doctrinal clarity requires careful differentiation between obligations grounded in investment treaties and good faith as a general principle of international law.

Under FET, tribunals frequently assess whether State conduct was arbitrary, inconsistent, or lacking transparency. Although the language of good faith is often employed, the legal source of the obligation is the treaty itself, not general international law. Legitimate expectations, for example, are protected only where the treaty standard so provides and where the investor relied on specific assurances attributable to the host State. Good faith here informs interpretation and application of the treaty standard; it does not independently generate investor rights (Dolzer and Schreuer 2012).

Procedural fairness offers a similar illustration. Requirements of due process, transparency, and consistency in administrative decision-making are often framed in good-faith terms. Yet their binding force derives from the applicable investment treaty or incorporated international standards. Treating these obligations as flowing directly from general international law would conflate distinct normative bases and risk category error. Good faith operates as an interpretive and evaluative tool, ensuring that treaty standards are applied coherently and without opportunism, while respecting the limits of consent (Schill 2009).

This differentiation matters for systemic coherence. Investment tribunals that anchor good-faith reasoning in treaty text preserve the balance between investor protection and regulatory autonomy. Where good faith is treated as an autonomous source of obligations, legal certainty is weakened and the legitimacy of the regime is placed under strain.

10.2 Law of the Sea and Boundary-Making

In the law of the sea, good faith performs distinct and recurring work, particularly in contexts of overlapping entitlements and unsettled boundaries. The United Nations Convention on the Law of the Sea embeds good-faith logic through duties of cooperation, the requirement of due regard for the rights of other States, and the framework for equitable delimitation (United Nations Convention on the Law of the Sea 1982).

Good faith is most visible during periods of pending delimitation. Where maritime boundaries have not yet been agreed, States remain entitled to exercise certain rights, such as resource exploration within claimed zones. However, good faith constrains these activities by excluding conduct that would jeopardise or hamper the reaching of a final agreement. Strategic acceleration of exploitation, irreversible alteration of the seabed, or unilateral actions designed to create faits accomplis may breach this constraint.

The concept of due regard reflects this function. It requires States to take account of the rights and interests of others when exercising their own entitlements. Good faith supplies the behavioural standard that gives due regard to practical content, preventing purely formal reliance on jurisdictional claims to justify conduct that undermines cooperative settlement (Churchill and Lowe 1999).

In boundary-making itself, good faith influences equitable delimitation reasoning. While delimitation is governed by legal principles and methods, good faith underpins expectations of consistency, transparency, and respect for provisional arrangements. It does not dictate outcomes, but it constrains strategic behaviour that would distort the process or entrench advantage before legal resolution.

10.3 Environmental and Climate-Related Cooperation

Environmental and climate-related regimes rely heavily on cooperation, reporting, and review mechanisms rather than coercive enforcement. In this context, the Principle of Good Faith in International Law operates less as a sanctioning device and more as a compliance culture tool.

Good faith supports transparency in reporting obligations. States are expected to provide accurate, complete, and timely information regarding emissions, environmental impact, or conservation measures. Manipulation of data, selective disclosure, or cosmetic compliance undermines the cooperative logic of these regimes and may constitute bad faith even where formal reporting requirements are met (Birnie, Boyle and Redgwell 2009).

Good faith also informs cooperative duties. Environmental obligations often require consultation, information exchange, and coordination in good faith, particularly where transboundary harm is at issue. These duties do not guarantee substantive agreement, but they exclude unilateralism that disregards the interests of affected States.

The relationship between good faith and due diligence is especially important. Due diligence defines the substantive standard of care required to prevent environmental harm. Good faith complements this standard by shaping how States organise compliance, engage with monitoring processes, and respond to identified risks. It does not replace due diligence, but it ensures that due diligence obligations are pursued honestly rather than strategically minimised.

Across these regimes, good faith does distinct work by sustaining cooperative frameworks that depend on trust rather than coercion. Its function is not to elevate aspirational goals into binding outcomes, but to ensure that agreed processes are not hollowed out by manipulation or performative compliance.

Taken together—without collapsing doctrinal boundaries—these selected contexts demonstrate how the Principle of Good Faith in International Law adapts to different legal environments. Its strength lies in its capacity to discipline conduct while remaining anchored to specific legal regimes and the consent that underpins them.

11. Operational Tests and Proof

11.1 A Practitioner’s Checklist for Pleading or Resisting Good-Faith Claims

Despite its abstract reputation, the Principle of Good Faith in International Law is applied through structured legal reasoning. Successful invocation or resistance requires disciplined proof rather than rhetorical appeal. International practice supports a stepwise analytical framework that can be articulated as a practitioner’s checklist.

The first step is to identify the primary rule engaged. Good faith does not operate in a vacuum. The claimant must anchor the argument in a specific treaty provision, customary rule, or recognised obligation. Courts consistently reject free-standing good-faith claims that are detached from an identifiable legal framework. This step determines the scope and limits within which good faith may operate.

The second step is to specify the alleged opportunistic move. The claimant must describe precisely how the opposing State’s conduct exploits formal legality to undermine the function of the primary rule. Vague allegations of unfairness or bad motives are insufficient. What matters is the objective structure of conduct: inconsistency, strategic sequencing, procedural manipulation, or reliance-frustrating behaviour (Kolb 2017).

The third step is to demonstrate reliance or prejudice, where relevant. In contexts such as estoppel, unilateral acts, or negotiation duties, proof of reasonable reliance or concrete prejudice significantly strengthens a good-faith claim. Reliance must be causally linked to the impugned conduct and reasonable in light of the circumstances.

The fourth step is to prove clarity and knowledge. The conduct relied upon must have been sufficiently clear to justify reliance, and the acting State must have known, or reasonably been expected to know, the legal and factual context. Ambiguity weakens good-faith claims, as international law does not readily infer obligations from uncertain signals (McNair 1961).

The fifth step is to justify the remedy sought. Good faith does not dictate remedies automatically. The claimant must show why the proposed consequence is proportionate and legally appropriate in light of the primary rule. Overreaching remedies risk transforming good faith into a substitute for substantive law and are frequently resisted by tribunals.

This structured approach reflects judicial caution. It ensures that good faith remains a tool of disciplined legal analysis rather than a rhetorical shortcut.

11.2 Remedies and Consequences

When a breach of good faith is established, the legal consequences vary according to context and the primary rule involved. International practice reveals a limited but coherent catalogue of outcomes.

One frequent consequence is interpretive narrowing. Courts may reject an interpretation that enables opportunistic conduct and adopt a reading that preserves the integrity of the obligation. This remedy is common in treaty interpretation and avoids formal declarations of breach where clarification suffices (Gardiner 2015).

Another consequence is preclusion, most notably through estoppel. A State may be barred from asserting a legal position inconsistent with its prior representations or conduct where reliance has occurred. This outcome stabilises legal relations without creating new obligations.

In clearer cases, tribunals may issue a declaration of breach. Such declarations reaffirm the existence of the obligation and clarify the limits of lawful conduct. They often serve a normative and preventive function even where coercive enforcement is unavailable.

Courts may also order or reaffirm duties to negotiate in good faith. This remedy is particularly common where ongoing cooperation is required and where rigid adjudication would be counterproductive. The order does not compel agreement but frames the process within legal parameters.

Where material harm has resulted, good faith may influence reparation consequences. While reparation follows from breach of a primary obligation, bad-faith conduct may affect the assessment of causation, scope of injury, or modalities of reparation, particularly in relation to cooperation and mitigation (Crawford 2013).

Finally, tribunals may impose procedural sanctions. These include adverse inferences, dismissal of abusive claims, or allocation of costs. Such measures protect the integrity of adjudication and deter procedural manipulation.

Across these outcomes, a consistent pattern emerges. Good faith shapes remedies proportionately and contextually. It does not create punitive consequences detached from substantive law. Its remedial function is to restore coherence, protect reliance, and reinforce the credibility of international legal processes.

Also read

• The Vienna Convention on the Law of Treaties 

• International Responsibility in Public International Law 

• The Sources Of International Law 

• Peaceful Settlement of International Disputes 

• Customary International Law: How It Forms and Works 

• Economic Sanctions under International Law: Legality and Limits 

• US v. Iran Hostage Case: Diplomacy, State Responsibility 

• Difference between ICJ and ICC: Jurisdiction, Power, and Limits

12. Critiques, Limits, and Responsible Use

12.1 Indeterminacy and the “Overworked” Principle Problem

The principal critique directed at the Principle of Good Faith in International Law concerns indeterminacy. Because good faith is framed in open-ended terms, there is a persistent risk that it becomes an all-purpose label for judicial preference rather than a disciplined legal standard. When invoked without clear anchoring, good faith may conceal discretionary reasoning under the appearance of legality, weakening predictability and confidence in adjudication (Kolb 2017).

This “overworked” principle problem arises when good faith is treated as a substitute for detailed legal analysis rather than as a complement to it. Courts may be tempted to invoke good faith to resolve hard cases where positive law appears inconclusive, especially in politically sensitive disputes. Without clear criteria, such use risks transforming good faith into a moralising device detached from consent and textual authority.

International practice demonstrates several techniques for avoiding this danger. First, good faith must be tethered to an identifiable legal rule. Tribunals should specify the primary obligation, interpretive framework, or procedural duty within which good faith operates. Second, its application must be fact-specific and evidence-based. Abstract references to fairness or reasonableness are insufficient; the analysis must identify concrete conduct that undermines reliance, consistency, or procedural integrity. Third, courts must articulate why good faith is legally relevant in the case at hand, rather than treating it as a rhetorical conclusion (Shaw 2017).

By adhering to these constraints, tribunals preserve good faith as a legal tool rather than an equitable shortcut. The principle retains normative force precisely because it is not free-floating. Its credibility depends on disciplined use.

12.2 Consent, Certainty, and the Boundary with Equity

A second, closely related limit concerns the relationship between good faith, consent, and equity. International law is grounded in State consent, expressed through treaties and accepted rules. Legal certainty depends on the ability of States to rely on the content of their obligations as negotiated. Good faith must operate within this framework.

Good faith can legitimately control abuse, clarify meaning, and discipline performance. It can exclude opportunistic readings of treaties, prevent manipulation of procedural rights, and protect reliance generated by clear conduct. What it cannot do is rewrite bargains or manufacture obligations in the absence of a legal basis. When good faith is used to impose substantive outcomes not grounded in consent, it ceases to be an interpretive or corrective principle and becomes a vehicle for equity in disguise (Bin Cheng 1953).

The boundary with equity is therefore critical. Equity in international law has a recognised but limited role, often explicitly provided for in specific contexts see, for example, maritime delimitation. Good faith does not import general equitable balancing into every dispute. It operates through law, not above it. Its function is to ensure that legal rules are applied honestly and coherently, not to replace them with judicial assessments of fairness.

Responsible use of the Principle of Good Faith in International Law thus requires constant attention to consent and certainty. When anchored to identifiable rules and applied with restraint, good faith enhances the legitimacy and effectiveness of international law. When detached from these anchors, it risks eroding the very stability it is meant to protect.

13. Conclusion

The analysis developed in this article confirms that the Principle of Good Faith in International Law is neither a marginal ethical notion nor a free-standing source of obligation. It is a pervasive legal standard that operates across treaty law, unilateral acts, negotiations, dispute settlement, State responsibility, and specialised regimes. Its doctrinal function is precise: to secure the reliability of international commitments and to restrain opportunism where formal legality would otherwise permit manipulation.

Good faith does not displace consent. It presupposes the existence of primary rules and derives its authority from their structure and purpose. In treaty relations, it disciplines formation, performance, and interpretation without transforming signature into obligation or interpretation into revision. In unilateral acts and reliance-based doctrines, it protects trust only where States have clearly chosen to generate it. In negotiations and procedure, it ensures the integrity of the process without compelling agreement or outcomes. In State responsibility and countermeasures, it constrains enforcement while preserving accountability.

The unifying feature across these contexts is restraint. International courts and tribunals have consistently treated good faith as a control principle rather than as a creative engine. Its application is fact-sensitive, evidence-based, and bounded by legal criteria. When invoked responsibly, it enhances legal certainty by preventing extreme formalism and strategic abuse. Where invoked without anchoring, it risks degenerating into discretionary equity and undermining predictability.

The doctrinal bottom line is therefore clear. The Principle of Good Faith in International Law is indispensable to the functioning of a decentralised legal order built on consent and cooperation. It sustains confidence that commitments will be honoured as understood, while ensuring that law cannot be reduced to technical avoidance. At the same time, its legitimacy depends on disciplined use. Good faith remains subordinate to, and constrained by, specific primary rules. Its strength lies not in replacing law, but in making law workable.

References

1. Aust, A. (2013) Modern Treaty Law and Practice. 3rd edn. Cambridge: Cambridge University Press.

2. Bin Cheng, B. (1953) General Principles of Law as Applied by International Courts and Tribunals. London: Stevens & Sons.

3. Birnie, P., Boyle, A. and Redgwell, C. (2009) International Law and the Environment. 3rd edn. Oxford: Oxford University Press.

4. Churchill, R.R. and Lowe, A.V. (1999) The Law of the Sea. 3rd edn. Manchester: Manchester University Press.

5. Crawford, J. (2013) State Responsibility: The General Part. Cambridge: Cambridge University Press.

6. Dolzer, R. and Schreuer, C. (2012) Principles of International Investment Law. 2nd edn. Oxford: Oxford University Press.

7. Fitzmaurice, G. (1957) ‘The Law and Procedure of the International Court of Justice’, British Yearbook of International Law, 33, pp. 1–65.

8. Gardiner, R. (2015) Treaty Interpretation. 2nd edn. Oxford: Oxford University Press.

9. International Court of Justice (1962) Case Concerning the Temple of Preah Vihear (Cambodia v Thailand), Judgment of 15 June 1962. The Hague: ICJ.

10. International Court of Justice (1974) Nuclear Tests (Australia v France; New Zealand v France), Judgments of 20 December 1974. The Hague: ICJ.

11. International Court of Justice (1997) Gabčíkovo–Nagymaros Project (Hungary v Slovakia), Judgment of 25 September 1997. The Hague: ICJ.

12. International Law Commission (2001) Articles on Responsibility of States for Internationally Wrongful Acts, with Commentaries. Yearbook of the International Law Commission, 2001, vol. II, Part Two. New York: United Nations.

13. Kolb, R. (2017) Good Faith in International Law. Oxford: Oxford University Press.

14. McNair, A. (1961) The Law of Treaties. Oxford: Clarendon Press.

15. Olleson, S. (2015) The Impact of the ILC’s Articles on State Responsibility. Oxford: Oxford University Press.

16. Oppenheim, L. (1992) International Law. 9th edn. Edited by R. Jennings and A. Watts. London: Longman.

17. Schill, S.W. (2009) The Multilateralization of International Investment Law. Cambridge: Cambridge University Press.

18. Shaw, M.N. (2017) International Law. 8th edn. Cambridge: Cambridge University Press.

19. Statute of the International Court of Justice (1945). San Francisco.

20. United Nations Charter (1945). San Francisco.

21. United Nations Convention on the Law of the Sea (1982). Montego Bay.

22. Vienna Convention on the Law of Treaties (1969). Vienna.