Sources of International Law: Treaties and Customs
Definition of Sources of International Law
Sources of law refer to the processes through which legal rules are created, modified, or extinguished. In international law, sources are identified in Article 38 of the Statute of the International Court of Justice (ICJ), which defines them as follows:
- International conventions: General or specific agreements that establish rules explicitly recognized by disputing states.
- International custom: Practices generally accepted as law.
- General principles of law: Recognized by “civilized nations.”
- Judicial decisions and scholarly opinions: Used as secondary means for interpreting law.
This classification suggests a distinction between primary sources (treaties, customs, and general principles) and auxiliary sources (case law and academic doctrine), with only the primary sources considered authentic sources of law. Notably, Article 38 does not specify any hierarchy among sources, implying that they hold the same normative status and that judges should consider all when settling disputes. However, specific customs, whether regional or local, take precedence over general customs.
International Custom
An international custom is a practice that international actors follow and generally accept as legally binding. Custom consists of two elements: the material element, which is the repetition of acts or consistent practice, and the spiritual element or “opinio juris,” the belief that the practice is legally binding. While the necessity of opinio juris is debated, it is widely accepted as part of customary law’s foundation. Custom has traditionally been the main source of international law, though codification has lessened its role.
Customs can be grouped into:
- Negative customs: Formed by abstention or non-action, as in the Lotus case (1927), where Turkey exercised jurisdiction over a French vessel in the absence of a legal prohibition.
- General customs: Apply to the entire international community and are universally binding unless opposed.
- Particular customs: May be regional or local, binding only on specific groups of States.
International Treaties
According to the Vienna Convention on the Law of Treaties (1969), a treaty is an agreement in written form between States and governed by international law. Treaties must:
- Be written, regardless of their form or title (e.g., agreements or protocols).
- Create legal obligations for the parties, excluding purely political commitments.
Treaties can be classified based on:
- Number of participants (bilateral or multilateral).
- Scope (universal or regional).
- Subject matter (such as human rights or trade).
- Function (treaty-laws that set norms versus treaties-contracts that involve an exchange of services).
- Participants (between States, organizations, or other subjects).
- Duration (fixed-term, indefinite, or renewable).
The process of forming a treaty generally involves four stages: negotiation, adoption of text, authentication, and consent through ratification or accession.
Treaty-Making Competence and the Role of Domestic Law
The Vienna Convention (Article 7) designates Heads of State, Heads of Government, and Ministers of Foreign Affairs as the principal figures authorized to conclude treaties. In Spain, the Spanish Constitution of 1978 assigns the power to conclude treaties to the Government, although certain treaties require prior authorization from the Spanish Parliament, particularly those with political or military significance.
A treaty conflicting with the Spanish Constitution requires constitutional reform prior to ratification. For instance, the Treaty of the European Union (1992) required an amendment to Article 13.2 of the Spanish Constitution to allow non-nationals voting rights in local elections.
Entry into Force and the Primacy of International Law
The entry into force of a treaty usually aligns with the moment of consent or an agreed date. Multilateral treaties, however, may require a specific number of ratifications. Rules around the entry into force include:
- Non-retroactivity: Unless otherwise specified, treaties are not retroactive.
- Good faith: States must refrain from actions that would undermine the treaty between consent and entry into force.
- Territorial application: By default, treaties apply throughout a State’s territory but may cover broader or limited areas.
If conflicts arise between treaties, Article 103 of the UN Charter prioritizes UN obligations over other treaties.
Reservations to Treaties
According to the Vienna Convention, a reservation is a unilateral statement by which a State excludes or modifies the legal effects of specific treaty provisions for itself. Key points on reservations:
- Applicability: Only relevant to multilateral treaties.
- Authorization: Can be explicit or implicit, but reservations incompatible with the treaty’s purpose are not valid.
- Legal impact: Reservations can lead to partial application of a treaty among States based on their acceptance or rejection of the reservation.
Interpretation, Amendment, and Modification of Treaties
The purpose of treaty interpretation is to clarify its content, primarily following Article 31 of the Vienna Convention, which mandates interpretation in good faith, considering the treaty’s ordinary meaning, context, and purpose.
Treaties may be amended to adapt to new circumstances, affecting all parties, while modifications are agreements between some parties that do not alter the obligations of other States.
Treaty Suspension, Termination, and Nullity
Suspension, termination, and nullity create temporary or permanent disengagement from treaty obligations. The Vienna Convention outlines valid reasons for these actions:
- Nullity: Includes coercion, use of force, or a violation of jus cogens.
- Suspension: Temporarily ceases treaty effects, possibly by mutual agreement or implied by the treaty’s text.
- Termination: Occurs by mutual consent, material breach, impossibility of performance, or fundamental change in circumstances.
In cases where a State’s withdrawal from a treaty is allowed, conditions may be specified in the treaty or inferred from its nature.
Unilateral Acts in International Law
Unilateral acts are binding commitments by a State, independent of the consent of other States. The Nuclear Tests Case (1974) by the ICJ established that unilateral acts must be public, involve intent to be bound, and be issued by a competent authority. Unilateral acts include recognition (of new States), promises, waivers, notifications, protests, and acquiescence (inaction in response to another State’s action).
General Principles, Doctrine, and Jurisprudence
The general principles of law are foundational norms recognized across legal systems worldwide. The International Court of Justice and Court of the European Union often rely on these principles when customary or treaty law is insufficient.
Scientific doctrine and international jurisprudence (judicial decisions) are auxiliary sources of law, aiding in the interpretation of primary sources. Judicial decisions, however, are binding only on the parties involved, according to Article 59 of the ICJ Statute.
Equity as a Source of International Law
The ICJ may rule ex aequo et bono (based on fairness) if the parties agree, applying principles of equity rather than strict legal rules.
Resolutions of International Organizations
International organizations, primarily created by treaties, can issue resolutions that bind their members, especially in organizations like the UN. Though not a source under Article 38 of the ICJ Statute, resolutions establish obligations and operational rules for their members.