Sources of international law are the materials and processes out of which the rules and principles regulating the international community are developed. They have been influenced by a range of political and legal theories. During the 19th century, it was recognised by legal positivists that a sovereign could limit its authority to act by consenting to an agreement according to the principle pacta sunt servanda. This consensual view of international law was reflected in the 1920 Statute of the Permanent Court of International Justice, and preserved in Article 38(1) of the 1946 Statute of the International Court of Justice.
Article 38(1) is generally recognised as a definitive statement of the sources of international law. It requires the Court to apply, among other things, (a) international conventions "expressly recognized by the contesting states", and (b) "international custom, as evidence of a general practice accepted as law". To avoid the possibility of non liquet, sub-paragraph (c) added the requirement that the general principles applied by the Court were those that had been "the general principles of the law recognized by civilized nations". As it is states that by consent determine the content of international law, sub-paragraph (d) acknowledges that the Court is entitled to refer to "judicial decisions" and the most highly qualified juristic writings "as subsidiary means for the determination of rules of law".
On the question of preference between sources of international law, rules established by treaty will take preference if such an instrument exists. It is also argued however that international treaties and international custom are sources of international law of equal validity; this is that new custom may supersede older treaties and new treaties may override older custom. Certainly, judicial decisions and juristic writings are regarded as auxiliary sources of international law, whereas it is unclear whether the general principles of law recognized by 'civilized nations' should be recognized as a principal or auxiliary source of international law.
It may be argued that the practice of international organizations, most notably that of the United Nations, as it appears in the resolutions of the Security Council and the General Assembly, are an additional source of international law, even though it is not mentioned as such in Article 38(1) of the 1946 Statute of the International Court of Justice. Article 38(1) is closely based on the corresponding provision of the 1920 Statute of the Permanent Court of International Justice, thus predating the role that international organizations have come to play in the international plane. That is, the provision of Article 38(1) may be regarded as dated, and this can most vividly be seen in the mention made to 'civilized nations', a mentioning that appears all the more quaint after the decolonization process that took place in the early 1960s and the participation of nearly all nations of the world in the United Nations.
It is also possible, though less common, for a treaty to be modified by practices arising between the parties to that treaty. The other situation in which a rule would take precedence over a treaty provision would be where the rule has the special status of being part of the jus cogens.
 International custom
Article 38.1(b) of the ICJ Statute refers to "international custom" as a source of international law, specifically emphasizing the two requirements of state practice plus acceptance of the practice as obligatory or opinio juris sive necessitatis (usually abbreviated as opinio juris).
Derived from the consistent practice of (originally) Western states accompanied by opinio juris (the conviction of States that the consistent practice is required by a legal obligation), customary international law is differentiated from acts of comity by the presence of opinio juris (although in some instances, acts of comity have developed into customary international law, i.e. diplomatic immunity). Treaties have gradually displaced much customary international law. This development is similar to the replacement of customary or common law by codified law in municipal legal settings, but customary international law continues to play a significant role in international law.
 State practice
When examining state practice to determine relevant rules of international law, it is necessary to take into account every activity of the organs and officials of states that relate to that purpose. There has been continuing debate over where a distinction should be drawn as to the weight that should be attributed to what states do, rather than what they say represents the law. In its most extreme form, this would involve rejecting what states say as practice and relegating it to the status of evidence of opinio juris. A more moderate version would evaluate what a state says by reference to the occasion on which the statement was made. It is only relatively powerful countries with extensive international contacts and interests that have regular opportunities of contributing by deed to the practice of international law. The principal means of contribution to state practice for the majority of states will be at meetings of international organisations, particularly the UN General Assembly, by voting and otherwise expressing their view on matters under consideration. Moreover, there are circumstances in which what states say may be the only evidence of their view as to what conduct is required in a particular situation.
The notion of practice establishing a customary rule implies that the practice is followed regularly, or that such state practice must be "common, consistent and concordant". Given the size of the international community, the practice does not have to encompass all states or be completely uniform. There has to be a sufficient degree of participation, especially on the part of states whose interests are likely be most affected, and an absence of substantial dissent. There have been a number of occasions on which the ICJ has rejected claims that a customary rule existed because of a lack of consistency in the practice brought to its attention.
Within the context of a specific dispute, however, it is not necessary to establish the generality of practice. A rule may apply if a state has accepted the rule as applicable to it individually, or because the two states belong to a group of states between which the rule applies.
A dissenting state is entitled to deny the opposability of a rule in question if it can demonstrate its persistent objection to that rule, either as a member of a regional group or by virtue of its membership of the international community. It is not easy for a single state to maintain its dissent. Also, rules of the jus cogens have a universal character and apply to all states, irrespective of their wishes.
Demand for rules that are responsive to increasingly rapid changes has led to the suggestion that there can be, in appropriate circumstances, such a concept as "instant custom". Even within traditional doctrine, the ICJ has recognised that passage of a short period of time is not necessarily a bar to the formation of a new rule. Because of this, the question is sometimes raised as to whether the word "custom" is suitable to a process that could occur with great rapidity.
 Opinio juris
A wealth of state practice does not usually carry with it a presumption that opinio juris exists. âNot only must the acts concerned amount to a settled practice, but they must also be such, or be carried out in such a way, as to be evidence of a belief that this practice is rendered obligatory by the existence of a rule of law requiring it.â
In cases where practice (of which evidence is given) comprises abstentions from acting, consistency of conduct might not establish the existence of a rule of customary international law. The fact that no nuclear weapons have been used since 1945, for example, does not render their use illegal on the basis of a customary obligation because the necessary opinio juris was lacking.
Although the ICJ has frequently referred to opinio juris as being an equal footing with state practice, the role of the psychological element in the creation of customary law is uncertain.
 Jus cogens
A peremptory norm or jus cogens (Latin for "compelling law" or "strong law") is a principle of international law considered so fundamental that it overrides all other sources of international law, including even the Charter of the United Nations. The principle of jus cogens is enshrined in Article 53 of the Vienna Convention on the Law of Treaties:
- For the purposes of the present Convention, a peremptory norm of general international law 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 which can be modified only by a subsequent norm of general international law having the same character.
Rules of jus cogens generally require or forbid the state to do particular acts or respect certain rights. However, some define criminal offences which the state must enforce against individuals. Generally included on lists of such norms are prohibitions of such crimes and internationally wrongful acts as waging aggressive war, war crimes, crimes against humanity, piracy, genocide, apartheid, slavery and torture.
The evidence supporting the emergence of a rule of jus cogens will be essentially similar to that required to establish the creation of a new rule of customary international law. Indeed, jus cogens could be thought of as a special principle of custom with a superadded opinio juris. The European Court of Human Rights has stressed the international public policy aspect of the jus cogens.
 Treaties as law
Treaties can play the role of contracts between two or more parties, such as an extradition treaty or a defence pact. Treaties can also be legislation to regulate a particular aspect of international relations, or form the constitutions of international organisations. Whether or not all treaties can be regarded as sources of law, they are sources of obligation for the parties to them. Article 38(1)(a), which uses the term "international conventions", concentrates upon treaties as a source of contractual obligation but also acknowledges the possibility of a state expressly accepting the obligations of a treaty to which it is not formally a party.
For a treaty-based rule to be a source of law, rather than simply a source of obligation, it must either be capable of affecting non-parties or have consequences for parties more extensive than those specifically imposed by the treaty itself.
 Treaties as custom
Some treaties are the result of codifying existing customary law, such as laws governing the global commons, and jus ad bellum. While the purpose is to establish a code of general application, its effectiveness depends upon the number of states that ratify or accede to the particular convention. Relatively few such instruments have a sufficient number of parties to be regarded as international law in their own right. The most obvious examples are the 1949 Geneva Conventions for the Protection of War Victims.
Most multi-lateral treaties fall short of achieving such a near universal degree of formal acceptance, and are dependent upon their provisions being regarded as representing customary international law and, by this indirect route, as binding upon non-parties. This outcome is possible in a number of ways:
- When the treaty rule reproduces an existing rule of customary law, the rule will be clarified in terms of the treaty provision. A notable example is the Vienna Convention on the Law of Treaties 1969, which was considered by the ICJ to be law even before it had been brought into force.
- When a customary rule is in the process of development, its incorporation in a multilateral treaty may have the effect of consolidating or crystallising the law in the form of that rule. It is not always easy to identify when this occurs. Where the practice is less developed, the treaty provision may not be enough to crystallise the rule as part of customary international law.
- Even if the rule is new, the drafting of the treaty provision may be the impetus for its adoption in the practice of states, and it is the subsequent acceptance of the rule by states that renders it effective as part of customary law. If a broad definition is adopted of state practice, the making of a treaty would fall within the definition. Alternatively, it is possible to regard the treaty as the final act of state practice required to establish the rule in question, or as the necessary articulation of the rule to give it the opinio juris of customary international law.
- Convention-based "instant custom" has been identified by the ICJ on several occasions as representing customary law without explanation of whether the provision in question was supported by state practice. This has happened with respect to a number of provisions of the Vienna Convention on the Law of Treaties 1969. If "instant custom" is valid as law, it could deny to third parties the normal consequences of non-accession to the treaty.
 General principles of law
The scope of general principles of law, to which Article 38(1) of the Statute of the ICJ refers, is unclear and controversial but may include such legal principles that are common to a large number of systems of municipal law. Given the limits of treaties or custom as sources of international law, Article 38(1) may be looked upon as a directive to the Court to fill any gap in the law and prevent a non liquet by reference to the general principles.
In earlier stages of the development of international law, rules were frequently drawn from municipal law. In the 19th century, legal positivists rejected the idea that international law could come from any source that did not involve state will or consent, but were prepared to allow for the application of general principles of law, provided that they had in some way been accepted by states as part of the legal order. Thus Article 38(1)(c), for example, speaks of general principles "recognised" by states. An area that demonstrates the adoption of municipal approaches is the law applied to the relationship between international officials and their employing organisations, although today the principles are regarded as established international law.
The significance of general principles has undoubtedly been lessened by the increased intensity of treaty and institutional relations between states. Nevertheless, the concepts of estoppel and equity have been employed in the adjudication of international disputes. For example, a state that has, by its conduct, encouraged another state to believe in the existence of a certain legal or factual situation, and to rely upon that belief, may be estopped from asserting a contrary situation in its dealings. The principle of good faith was said by the ICJ to be "[o]ne of the basic principles governing the creation and performance of legal obligations". Similarly, there have been frequent references to equity. It is generally agreed that equity cannot be employed to subvert legal rules (that is, operate contra legem). This "equity as law" perception is reinforced by references to equitable principles in the text of the United Nations Convention on the Law of the Sea 1982, though this may be little more than an admission as to the existence, and legitimation, of the discretion of the adjudicator.
However, the principles of estoppel and equity in the international context do not retain all the connotations they do under common law. The reference to the principles as "general" signify that, if rules were to be adapted from municipal law, they should be at a sufficient level of generality to encompass similar rules existing in many municipal systems. Principles of municipal law should be regarded as sources of inspiration rather than as sources of rules of direct application.
 Judicial decisions and juristic writings
According to Article 38(1)(d) of its Statute, the ICJ is also to apply "judicial decisions and the teachings of the most highly qualified publicists of the various nations, as subsidiary means for the determination of rules of law". It is difficult to tell what influence these materials have on the development of the law. Pleadings in cases before the ICJ are often replete with references to case law and to legal literature.
 Judicial decisions
The decisions of international and municipal courts and the publications of academics can be referred to, not as a source of law as such, but as a means of recognizing the law established in other sources. In practice the International Court of Justice does not refer to domestic decisions although it does invoke its previous case-law.
There is no rule of stare decisis in international law. The decision of the Court has no binding force except between the parties and in respect of that particular case. Nevertheless, often the Court would refer to its past decisions and advisory opinions to support its explanation of a present case.
Often the International Court of Justice will consider General Assembly resolutions as indicative of customary international law.
 Juristic writings
Article 38(1)(d) of the International Court of Justice Statute states that the 'teachings of the most highly qualified publicists of the various nations' are also among the 'subsidiary means for the determination of the rules of law'. The scholarly works of prominent jurists are not sources of international law but are essential in developing the rules that are sourced in treaties, custom and the general principles of law. This is accepted practice in the interpretation of international law and was utilised by the United States Supreme Court in The Paquete Habana case (175 US (1900) 677 at 700-1).
 See also
 Notes and references
- ^ Statute of the International Court of Justice.
- ^ D'Amato, A., The Concept of Custom in International Law (Cornell University Press: Ithaca, New York, 1971) at 88.
- ^ Thirlway, H., International Customary Law and its Codification (A. W. Sijthoff: Leiden, 1972) at 58.
- ^ See Case Concerning Military and Paramilitary Activities in and against Nicaragua (Nicaragua v United States of America) (Merits)  ICJ Reports 14.
- ^ Fisheries Jurisdiction Case (United Kingdom v Iceland) (Merits)  ICJ Reports 3 at 50.
- ^ North Sea Continental Shelf Cases (Federal Republic of Germany v Denmark; Federal Republic of Germany v Netherlands)  ICJ Reports 4 at 42.
- ^ Nicaragua case (Merits), note 4 at 98.
- ^ Asylum Case (Colombia v Peru)  ICJ Rep 266 at 277; Advisory Opinion on the Legality of the Threat or Use by a State of Nuclear Weapons in Armed Conflict  ICJ Reports 226.
- ^ Case Concerning Right of Passage over Indian Territory (Portugal v India) (Merits)  ICJ Reports 6 at 39; Asylum case, note 8 at 276.
- ^ North Sea Continental Shelf cases, note 6 at 229, 232 per Judge Lachs.
- ^ Asylum case, note 8 at 277-8.
- ^ Fisheries Case (United Kingdom v Norway) (Judgment)  ICJ Reports 116, at 131.
- ^ See North Sea Continental Shelf cases, note 6 at 229 per Judge Lachs.
- ^ North Sea Continental Shelf cases, note 6 at 43.
- ^ See North Sea Continental Shelf cases, note 6 at 44.
- ^ Legality of Nuclear Weapons Advisory Opinion (GA), note 8.
- ^ Case Concerning the Continental Shelf (Libyan Arab Jamahiriya v Malta) (Judgment)  ICJ Reports 13 at 29; Legality of Nuclear Weapons Advisory Opinion (GA), note 8 at 16.
- ^ Legal Consequences for States of the Continued Presence of South Africa in Namibia (South-West Africa) notwithstanding Security Council Resolution 276 (1970) (Advisory Opinion)  ICJ Reports 16 at 47.
- ^ North Sea Continental Shelf cases, note 6 at 38.
- ^ North Sea Continental Shelf cases, note 6 at 41. See also Trial of the Major War Criminals before the International Military Tribunal, Vol. 1, Judgment, 171 at 253-4.
- ^ Amerasinghe, C., The Law of the International Civil Service, 2nd rev. edn, vol. 1 (Clarendon Press: Oxford, 1994) at 151-8.
- ^ See North Sea Continental Shelf cases, note 6 at 26; Flegenheimer Claim 25 ILR 91; Case Concerning the Temple of Preah Vihear (Cambodia v Thailand) (Merits)  ICJ Reports 6 at 32-3.
- ^ Nuclear Tests Cases (Australia v France; New Zealand v France)  ICJ Reports 253 at 268.
- ^ River Meuse Case (Netherlands v Belgium) PCIJ Reports Series A/B No 70 76 at 76 per Judge Hudson.
- ^ Case Concerning the Frontier Dispute (Burkina Faso v Republic of Mali) (Judgment)  ICJ Reports 554 at 567-8; North Sea Continental Shelf cases, note 6 at 46-50.
- ^ International Status of South-West Africa (Advisory Opinion)  ICJ Reports 128 at 148.
- ^ Article 59 of the ICJ Statute Statute of the International Court of Justice.
 Further reading
- Thirlway, H., International Customary Law and its Codification (A. W. Sijthoff: Leiden, 1972).
 External links