Sources of International Law are contained in Article 38 of the Statute of International Court of Justice
(ii) International Customs
(iii) General Principles of Law
(iiii) Judicial Decisions
These are generally said not to be a general source of law as they bind only the parties to the treaties. Additionally, treaties are voluntary in the sense that no State can be bound without having given its consent to be boundd
International Customs and its relationship to treaties can be explored in Colombia v Peru. 4 factors were considered in this case - generality, duration, constant and uniform and opinio juris
(i) Lotus Case: The formation of customary law must be reasonably consistent. However- the Anglo-Norwegian Fisheries Cases states that the degree of consistency will vary according to the subject matter of the case or rule in dispute
(ii) The State practice must be fairly general, it must be common to a significant number of states. Again, the degree of generality will vary according to the subject matter of the case. For example, the practice of those States whose interests are specifically affected by that rule may be given special weight. additionally, when a State from the outside objects to a particular practice, it seems that it may not be bound by an evolving customary rule.
An Objector will stop a State being bound by a customary rule. While it is true that persistent objection from one state will not prevent the formation of customary law, its continued objection prevents customary law being developed.
The International Court of Justice has not provided any clear guidelines on the time required for the consistent general practice to mature into customary law. Some writers argue that the persistent objector rule cannot escape being bound by a new rule of customary international law that has the character of jus cogens. In the Asylum Case, the Court recognised that Article 38 encompassed local custom as well as general custom.
Only a few International Courts and Tribunals have actually endorsed the concept of the persistent objector, and even then, only in obiter dicta or dissenting opinions.
The overwhelming majority of States never accepted the apartheid regimes of South Africa and the Republic of Rhodesia. Both countries had continuously objected the emergence of customary rules, prohibiting such racist regimes, but this did not protect them from increasing pressure from other States to conform to standards of International Law.
Unit 1 of International Law
Their Status as Objectors gave them legal protection against the pressure exerted by the International Community. Despite its criticism, some writers argue that the concept of the persistent obector is essential as it represents different conflicting views of International Law.
It is not enough for the formation of customary law that there is general, consistent State Practice. The State must recognise that practice to be binding it as Law. State Practice must be accompanied by the belief that the practice was obligatory rather than habitual.
In the Lotus case, the PCIJ empahasised that opinio juris was an essential element in the formation of customary law. This was reiterated in the North Sea Continental Shelf Cases and has been accepted since. In this case, the view was that Opinio Juriis could be presumed from consistent State Practice unless a contrary intention was apparent.
It is easy to cricism the requirement of Opinio Juris as it seems to play no part in the requirement of international law. Yet without its requirement, it would be impossible to determine where habit stopped and law began. Its importance has been affirmed in the ICJ decisions such as the Nicaragua case and the Gulf of Maine Case.
These are similar to general principles of common tlaw to national legal systems. Even if thse principles do not qualifyy as 'binding law' and some would argue that they do, it is not clear that such general principles may have a profound effect on the development of International Law.
These are described in Article 38 (1) (d) as a subsidiary means for the determination of law. They do not make Law but rather a declaration of pre-existing law. This is supported by s59 of the ICJ Statute.
It is inherent that in order for customary law to develop, there must be sufficient State practice to the existing rule, supported by Opinio Juris.
Necessarily, however, much of this State Practice will be regarded as action in breach of existing law because the customary norm has not yet changed. It is an unusual feature of the International Legal System that only through illegal conduct can some rules be modified or changed.
In such cases, opinio juris will play a pivotal role, in particulat, the manner in which the contrary conduct is received by international members of the International Community.
Firstly, if the conduct is not accepted by the international community at large, a State which accepts the conduct of another State that is in breach of an existing customary normal will be taken to have FORFEITED the right to complain of the breach.
This can be seen in Norway's use of the straight baseline method of maritime delimitation in the Norwegian Fisheries Case.
Secondly, it would be difficult to establish that a rule of jus cogens has been changed by contrary State Practice. Rules of jus cogens are said to be a fundamental rule of customary law in that not even a treaty can contradict. Any contrary conduct is likely to be regarded a as serious breach of international law.
Custom has been a source of international law for as long as States have been governed by legal rules
Treaty and Customary Law
Where treaty and customary law stipulates the same or similar legal obligations, there are a few disagreements. Parties to the treaty will have to be bound by the treaty and non parties will be bound by Customary Law.
Nicaragua Case - this makes it clear that custom will not cease to bind a State even if it is party to a treaty stipulating the same obligation. The USA and Nicaragua were bound by the prohibition of the use of armed force contained in the UN charter and a similar obligation in customary law.
Custom and Treaty Law
where treaty and custom law are in conflict, there has been some disagreement as to the effect this has on legal relations of the parties to a dispute.
(i) If the treaty is at a later time than the customary law, then the treaty will prevail
(ii) Where a treaty was made before the custom, it would be thought that the custom would prevail in this case. However, in Danube Dam Case - the ICJ was unable to synthesise later developments in customary law with the obligations contained in the UN Charter or between Slovakia and Hungary.
The rules of jus cogens are so fundamental that they cannot be changed by treaty. s.53 of the Vienna Convention states that any treaty provision conflicting with the rules of jus cogens are void, whether or not it was developed before or after the treaty was developed.