International law - Sources and Legal Hierarchy

Sources of International Law Introduction International law governs relationships between states and increasingly includes international organizations and individuals. But what makes something "law" at the international level? Unlike domestic legal systems with centralized legislatures and courts, international law emerges from several different sources. Understanding these sources is essential because exam questions will ask you to identify which legal obligations bind states and why. The main sources of international law are: treaties, customary international law, general principles of law, and judicial decisions and scholarly teachings (in subsidiary roles). Each source has different requirements for creation, different scope of applicability, and different interpretive rules. Treaty Law What is a Treaty? A treaty is a formal written agreement between states (and sometimes international organizations) that creates binding legal obligations. Treaties are the most explicitly consensual form of international law—states must affirmatively agree to be bound. The principle that makes treaties binding is pacta sunt servanda—Latin for "agreements must be kept." This means parties have a legal obligation to perform the treaty in good faith. Think of it as the foundational rule that makes international law work: if countries couldn't rely on other countries' promises, there would be no meaningful international legal system. How Do States Consent to Be Bound? States can express consent to be bound through several mechanisms: Signature - A state's representative signs the treaty, which typically indicates intent to be bound but is not yet a full commitment (though some treaties become binding upon signature). Ratification - The state's government formally approves a treaty after signature. Ratification is the most common final step for binding commitment and often requires legislative approval domestically. Acceptance or Approval - Alternative formal mechanisms that have the same effect as ratification. Accession - A state joins an already-negotiated treaty without having signed it, becoming bound directly to all terms. The reason these distinctions matter: not every signature means a treaty is binding. A country might sign to show support but then never ratify it, never becoming legally bound. This explains why you might read that a country "signed but didn't ratify" a treaty. How Are Treaties Interpreted? When disputes arise about what a treaty means, interpreters must decide between three approaches: Textual approach: Look at the ordinary meaning of the words used. What would a reasonable reader understand the words to mean? Subjective approach: Look at the intent of the drafters. What did the negotiating states intend when they agreed to these words? Teleological approach: Look at the object and purpose of the treaty. What is the treaty trying to accomplish? In practice, treaty interpretation uses a combination of these approaches rather than favoring one absolutely. Courts often start with the text but can refer to negotiating history or the treaty's broad purposes to clarify ambiguous language. This is important because it means you can't just read a treaty's words in isolation—context matters. Reservations and Declarations States sometimes want to modify how a treaty applies to them. They can do this through: Reservations - A state declares that it will not be bound by a specific provision (or will interpret it in a particular way). Reservations actually change the legal effect of that provision for that state. Interpretive declarations - A state clarifies how it understands a provision without excluding it. Conditional declarations - A state makes its binding commitment conditional on certain circumstances. The practical significance: a reservation means a country isn't bound by that part of the treaty the way other states are. This allows flexibility but can create a "patchwork" where the treaty doesn't apply uniformly. Treaty Termination and Withdrawal Treaties can end when: The treaty's term expires according to its own terms A bilateral treaty is terminated by agreement between the two parties A state withdraws from a multilateral treaty, usually by giving notice as specified in the treaty All parties agree to terminate it Article 54 of the Vienna Convention on the Law of Treaties governs this process. The key principle: you can't unilaterally exit a treaty just because you change your mind, except where the treaty itself allows withdrawal. When Are Treaties Invalid? A treaty can be declared invalid if: Ultra vires action - One state's representatives exceeded their authority when signing Fraud or coercion - A state was deceived or coerced into agreement Conflict with peremptory norms - The treaty violates jus cogens (discussed below), which override any treaty commitment This prevents obviously unfair or illegal treaties from creating binding obligations. Customary International Law The Two-Element Test Unlike treaties, customary international law emerges from state practice over time. It requires two elements: State practice - Consistent, uniform behavior by states over a significant period. This can include diplomatic practice, military conduct, legislation, or judicial decisions. Opinio juris (opinion of law) - The belief by states that this practice is required by law, not just done as a matter of convenience or habit. States must believe they're acting legally obligated, not merely being courteous. Both elements must be present. For example, if most countries observe a rule out of habit rather than legal obligation, it's not customary law—it's just custom. The psychological element (opinio juris) transforms practice into law. Example: The principle that territorial waters extend 12 nautical miles from the shore became customary law because states consistently claimed this distance and believed international law required it, not just preferred it. The Persistent Objector Doctrine One fascinating exception to customary law is the persistent objector doctrine. If a state continuously and explicitly objects to a developing norm throughout the period it's forming, that state may avoid being bound by the resulting customary rule—even after it becomes binding on other states. This doctrine recognizes that states shouldn't be trapped by legal developments they actively opposed from the beginning. However, it only works if the objection is: Consistent (expressed regularly) Persistent (maintained throughout the norm's development) Explicit (clearly stated) Once a customary norm is fully formed, new objections won't help—the objector is bound. Peremptory Norms (Jus Cogens) Some customary norms are so fundamental that no state can escape them through treaty or objection. These are peremptory norms or jus cogens (Latin: "compelling law"). They represent the international community's core values. Examples include: Prohibition on the use of force between states Prohibition on genocide Prohibition on slavery Prohibition on torture Right to self-determination The key characteristics: No derogation is permitted—you cannot contract out of them They override any conflicting treaty They are accepted by the international community as a whole No state can become a persistent objector to these norms This is why even if a state ratified a treaty allowing torture, that treaty would be void as conflicting with jus cogens. International law recognizes some principles as non-negotiable. Erga Omnes Obligations Related to peremptory norms are erga omnes obligations (Latin: "towards all"). These are duties owed to the international community as a whole, not just to individual states. Examples include: Prohibition of genocide Protection of fundamental human rights Environmental protection obligations The significance: if a state violates an erga omnes obligation, any state can bring a claim to the International Court of Justice, even if that state wasn't directly injured. This reflects the idea that some violations harm the international community itself, not just specific victims. Distinction to remember: Peremptory norms are about what law cannot be derogated. Erga omnes obligations are about who can enforce it. A norm can be both peremptory and erga omnes. General Principles of Law General principles of law are rules recognized by "civilized nations" (a dated but still-used term meaning all states) that are derived from commonalities in national legal systems. These are general legal ideas that appear across different countries' domestic laws, adapted to the international context. Examples include: The principle that no one can profit from their own wrongdoing Principles of good faith and fair dealing Estoppel (you cannot contradict your own previous position) Rules of evidence and procedure in dispute resolution These serve as a secondary source—when an issue isn't covered by treaty or customary law, courts might look to these general principles to fill the gap. They matter because international courts sometimes rely on them, especially when established law is silent. Judicial Decisions and Scholarly Teachings Judicial decisions of international courts and the writings of prominent scholars are not themselves sources of law, but rather subsidiary means for determining what the law is. When international courts (particularly the International Court of Justice) decide cases, those decisions don't create binding law for future cases (there's no precedent system in international law). However, courts' reasoned interpretations of treaties and customary law influence how international law develops and provides guidance on how rules should be understood. Similarly, treatises and articles by respected international legal scholars inform courts and states about the state of international law. While not binding, influential scholarship shapes how international law develops. The reason these are only subsidiary: allowing court decisions or scholarly opinions to be primary sources would create too much instability. Instead, they help interpret the actual sources (treaties and custom). Relationship Between International and National Law Here's a crucial question: when international law and a country's own domestic law conflict, which prevails? And how does international law become enforceable within a country's courts? The answer depends on whether a state follows monism or dualism. Monism: One Unified Legal Order Monist states treat international and national law as parts of a single, integrated legal order. In monist systems: Treaties become part of domestic law automatically upon ratification (no separate legislation needed) International law generally has higher status than conflicting domestic statutes Courts can directly apply international law This means a monist country's courts can enforce treaty provisions directly without the legislature passing implementing legislation. It's efficient and ensures international commitments are honored, but it can limit legislative control over what laws apply domestically. Dualism: Two Separate Legal Orders Dualist states treat international and national law as separate, independent legal systems. In dualist systems: Treaties must be incorporated into domestic law through legislative action before they have effect domestically A country can be bound internationally by a treaty while having no domestic law enforcing it Courts typically cannot apply treaty provisions directly; they need enabling legislation This means even if a country ratifies a treaty, citizens can't sue in domestic courts based on that treaty unless their legislature passes a law implementing it. It gives legislatures control but can make treaty compliance slower and less reliable. Hybrid Approaches: The Modern Reality Most modern states use hybrid systems: Peremptory norms and fundamental human rights obligations often apply automatically (monist approach) Other treaty obligations require legislative incorporation (dualist approach) Some states are broadly monist with specific dualist exceptions This flexibility allows states to benefit from international law's automatic application where it matters most (fundamental rights, prohibitions on grave crimes) while retaining legislative control over routine treaty implementation. The practical consequence: you cannot assume that because a country is bound by an international treaty, its courts will automatically enforce it. You must know whether that country is monist or dualist and what type of norm is involved.