Sources of international law include international conventions, international custom, and general principles of law recognised by civil States; judicial decisions and teachings of the most highly qualified jurists are subsidiary means of determining the rules of law.
International law may originate with international organisations such as the United Nations, which may themselves conclude treaties on behalf of groups of states.
International conventions and treaties are the pre-eminent sources of international law. There are numerous treaties between States and international organisations dealing with a wide range of issues and standards.
Treaties are commonly described as sources of law. States are subject to the rule of law, and when they bind themselves to conduct themselves in a particular way, the matter is fairly described as law.
Treaties may be bilateral in that they are entered between two parties or multilateral, where there are multiple parties.
A treaty is, in effect, an agreement between States in relation to aspects of international relations. Where a treaty imposes obligations, they must be fulfilled in accordance with their spirit and terms in good faith unless there is a defence available.
Most treaties are respected most of the time. They have been entered voluntarily and accepted voluntarily. A State is bound as regards other parties to the treaty. It is not bound as regards a third party.
Customary law is law that has evolved from the practice or custom of states. It is only in the last 40 years that treaties and conventions have replaced customary laws, as the primary source of international law. Many rules governing the relations of States are still based on customs.
Custom is analogous to common law. It may be available to fill voids in a written treaty. Customs may not gain universal acceptance. Customary law develops from the practice of States and other bodies and has an ongoing organic element and flexibility. It is not as defined as other sources of law. Multilateral treaties may embody a codification of existing customary law.
Customary law derives from State practice. Over time, State practice may be recognised and crystallised into customary law. Without State practice, there can be no customary law. State practice may be by way of acts or omissions, statements made in respect of positions, situations and disputes, from national legislation, and the practice of international organisations.
Practice must be sufficiently consistent and recurrent to form part of customary law. It must be constant or uniform or so-called settled practice. If different States declare different positions on the matter, this is inconsistent with customary law.
In the case of obligations, a greater degree of consistency is required for the formation of customary rules than in the case of passive obligations to refrain from doing something. Alleged changes in customary rules would require to be supported by almost universally consistent State practice. The more fundamental a customary rule, the more consistent State practice to the contrary there would require to be before it can dislodge it.
The existence of a State practice which may be contrary to an existing or emerging custom law is not of itself destructive of the principle. It could be evidence of a breach of a customary rule. Otherwise, any breach or deviation from the norm could be rationalised as an attempt to create new customary law.
Customary law may only relate to a practice which is fairly general and common to a significant number of States. No definite number or majority is required. The degree of generality will depend on the nature of the subject matter. The more onerous the obligation, the more general the practice that is required for it to be accepted as customary.
An objection may be relevant, but it cannot excuse unlawful conduct. Persistent objection over time may have an impact on customary law. Other States may acquiesce in the deviation so that the objector is absolved from liability to them.
There are no clear guidelines on the time required for consistent general State practice to become customary law. The length of time will depend on the subject matter. It is possible that a single act without repetition might be the basis of custom, although this would be unusual. It would require strong evidence that the states regard the new practice as binding.
State practice must be accompanied by a belief that it is obligatory, not merely habitual or convenient. This is termed opinio juris and has been stated by the International Court of Justice to be an essential element in the formation of customary law. It is said that this quality may not necessarily be inferred from frequent or even habitual practice and that it is a distinct, independent requirement.
The International Court of Justice has found the requisite opinio juris in the consistent practice of domestic courts and the statements of government. The degree of proof required for this element will depend on the subject matter. In some cases, repeated activity and a little more will suffice. The concept refers to the notion that habit must be more than mere practice and will have an implicit acceptance of legality.
The concept may appear tautologous as the issue in question is whether the custom, in fact, has the force of law. However, the belief and acting as if it has the force of law has significance beyond mere custom and act. It must be possible to infer a legal basis rather than mere habit and practice.
Customs may develop spontaneously with changing values. Customary law may develop over time. There must be sufficient State practice contrary to the existing rule supported by opinio juris. The initial development may be by way of a breach.
It is difficult to define when contrary conduct becomes customary in itself. A state which acquiesces in the conduct of another state that appears to be in breach of an existing norm may be taken to have forfeited the right to complain. The new practice may commence embodying a rule or principle between the states.
It is said that custom is based on the explicit or implicit consent of states. However, this is only true in part, as consenting States may never have the opportunity of objecting to the practice.
Customs, conventions and treaties may be complementary. They may deal with the same subject matter. There may be cases where a state is bound by both custom and treaty law where parallel obligations are provided by the treaty.
Treaties v Customary
Custom and fundamental customs jus cogens are fundamental rules which exist independent of treaty law. Where customs and treaties conflict, then the treaty is subject to the operation of jus cogens, and the treaty prevails. Non-parties may continue to be governed by customary law.
Where a contrary customary law develops subsequent to the treaty, the position is less clear. In principle, the later custom may prevail. However, this undermines the certainty of obligations deliberately and freely undertaken in a treaty.
Accordingly, a subsequent practice may amend the treaty in only the most exceptional circumstances where there is a clear consensus between the party that the treaty should be abandoned. The better view is that the treaty continues to govern the positions.
Where, however, the treaty conflicts with preemptory norms of general international law, jus cogens, the jus cogens may prevail.
The Vienna Convention on Treaties provides that a treaty is void if, at the time of its conclusion, it conflicts with the peremptory norms of general international law. This is a norm accepted and recognised by the international community of States as a whole, as a norm from which no derogation is permitted and can be modified only by a subsequent norm of general international law having the same character.
Fundamental Principles & Norms
These are principles so fundamental that they may not be modified by treaty. There is no universal agreement in relation to which customary rules have this status. A clear example would be the prohibition on the use of armed force in international relations prohibition of war crimes and crimes against humanity.
Other possible principles of this level include the sovereign equality of States, freedom of the high seas, rights to self-determination and the prohibition of genocide and torture.
The above principles may be said to incorporate elements of natural law principles into international law. Natural law rules are said to have pre-existing legal validity, independent of any legal system. The general principles may inform treaties.
On a broader view, general principles are an acknowledgement of sources of law outside the states’ control. On a narrow view, they merely describe general non-specific principles that are already validated by law, custom and treaty.
The principles ensure that international law includes rules and principles common to all legal systems. Examples are the right of persons to go to court to settle disputes, the right to be heard before judgment is pronounced, and the entitlement to receive compensation for proven injury. The principles must necessarily form part of international law.
A national law is not to be imported into international law wholesale but may provide an indication of the types of rules which might assist in ascertaining international law.
Principles of equity, justice and fairness have been long considered part of international law. Equitable solutions have been posited as a source of law. This is not to say that judges may exercise arbitrary discretion.
Decisions of the International Court of Justice are a source of subsidiary law. They do not alter it. The statute of the court indicates that the decision of the court is only binding between the parties. Although there is no formal doctrine of binding precedent, the court has great regard of regard, to its decision in previous cases and the manner in which it expounded the law in them. The court will generally follow its earlier decisions.
In almost all cases, decisions are more than guidelines but are authoritative as regards future decisions. Decisions of the court may have a profound effect. They may crystalise existing customary law or accelerate its crystalisation. They may have a decisive effect on subsequent State practice. They may indicate how the law is developing and how it should develop.
Reference may also be had to decisions of international panels, national courts, specialised institutions and regional courts such as the International Criminal Court, the Inter-American Court of Human Rights, The European Court of Human Rights, the Law of the Sea Tribunal, the African Court of Human and Peoples’ Rights and the Centre for Settlement of Investment Dispute.
The decisions of these bodies and similar bodies are generally binding between the parties but are also of considerable assistance in the development of certain areas of law.
National courts sometimes deal with matters of international law and provide important evidence on the practice of States, particularly in relation to matters such as State immunity, neutrality, extradition, and protection of human rights. They may provide authoritative guidance in relation to the status of alleged and existing customary law.
The writing of highly qualified jurists is a subsidiary source of international law. The writings of eminent jurists have been influential in the development of international law. This source of law is less important in modern times.
The writing of jurists may be of importance when a rule is vague and uncertain. The writing of jurists may have a direct impact on customary law in that they help establish the State practice of predicting trends and encouraging States to follow the predicted and desirable path.
UN Generally Assembly
The General Assembly is principally a political body, notwithstanding that it produces resolutions dealing with questions of international law. This is not its primary function. The general principle is that resolutions of the General Assembly are not binding even if unanimously adopted. A State need not necessarily follow matters set out in resolutions even if they voted for it.
The resolutions do matter in the context of the internal workings of the United Nations, its organs and organisations, each dealing with substantive questions of international law.
Some General Assembly resolutions may declare customary law. Although the resolution does not create the law, it may, in some cases, be looked to in relation to the underlying principles.
Soft law refers to rules of international law that do not provide concrete rights and obligations for legal entities to whom they are addressed. Their content is flexible or vague. They are found in non-traditional areas, such as treaties relating to human rights and environmental protection, where States may not wish to establish clear-cut rules.
Soft law of this nature may create incremental or relative obligations, obliging parties to take steps with a view to achieving the requisite standards progressively. In another sense, soft law may refer to guidelines, ideas and proposals that may develop into rules of international law but have not yet done so. They will only become law by customary treaty or other law-making processes.