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Customay International Law

Updated on April 18, 2015

Law and Custom

Custom in its legal sense means something more than habit or usage, it is a usage felt by those who follow it as obligatory. Customary international law (“CIL”) is one of two primary forms of international law, the other being the treaty. Customary international law is typically defined as a “customary practice of states followed from a sense of legal obligation.” Conventional wisdom views customary international law as a unitary phenomenon that pervades international law and international relations. Governments take care to comply with customary international law, and often incorporate its norms into domestic statutes. National courts apply customary international law as a rule of decision, or a defense, or a canon of statutory construction. The domestic enforceability of customary international law is manifest in the case of Filartiga v. Pena-Irala;two issues were made clear by this case. Firstly, customary international law is a matter of universal jurisdiction, so that any national courts may hear extra-territorial claims brought under international law. Secondly, domestic court may discover international legal principles by consulting executive, legislative and judicial precedents, international agreements, the recorded expertise of jurists and commentators, and other similar sources. In the case of Portugal v. India, the Rite of passage over Indian Territory was asserted on the basis of local custom and custom was established. .There also exist a class of customary international law, jus cogens, that has peremptory force and cannot be abrogated by domestic law or treaty. Jus cogens is generally deemed self-executing. When domestic courts apply treaty law and other rights established by express accord, they usually look to the language and legislative history of the norms involved to locate the intent to enforce them locally. If such intent exists, these agreements are regarded as self-executing.

The Circumstances

Customary rules crystallized from usages or practices which have evolved in approximately three sets of circumstances:

(a) Diplomatic relations between states: Thus acts or declarations by statesmen, opinions of legal advisers to state governments, bilateral treaties, and now press releases or official statements by government spokesmen may all constitute evidence of usages followed by states.
(b) Practice of International organs: The practice of international organs, again whether by conduct or declarations, may lead to the status, or their powers and responsibilities.
(c) State laws, decisions of state courts, and state military or administrative practices: A concurrence of state laws or of judicial decisions of state courts or of state practices may indicate so wide an adoption of similar rules as to suggest the general recognition of a broad principle of law. There are multifarious occasions on which persons that act or speak in the name of a state, do acts, or make declarations, which either express or imply some view on a matter of international law. Any such act or declaration may, so far as it goes, be some evidence that a custom, and therefore that a rule of international law, does or does not exists. Particularly important as sources of evidence are diplomatic correspondence, official instructions to diplomats, and consuls, and military commanders, acts of state legislation and decisions of state courts, which, we should presume, will not deliberately contravene any rule regarded as a rule of international law by the state. In applying these forms of evidence in order to establish the existence of an international custom, what we are looking for is a general recognition among states of a certain practice as obligatory. It would hardly ever be practicable and all but the strictest of positivists admit that is not necessary, to show that every state has recognized a certain practice. This test of general recognition is necessarily a vague one.

Elements of Customary Law

Custom is an international habit of actions that has received full length attestation. Usage represents twilight stage of customs. Thus, custom begins where usage ends. In nutshell, custom is such a usage as has force of law. Customary law has been evolved from the live out of the States. The actions of the states in the international arena give rise to obligatory law. The statue of International court of Justice describes customary law as a “general practice accepted by law”. As the International court stated in the Continental Shelf Case: “It is of course axiomatic that the material of customary international law is to be looked for primarily in the actual practice and opinion juris of the states.” Article 38 of the Statue of International Court of Justice states that the court should apply ‘international custom, as evidence of a general practice accepted as law’. The statue, therefore, contains two requirements for the existence of international custom, namely, first there should be a sufficiently uniform practice, and secondly the belief that such practice is obligatory.

State Practice

Any activity of the state can amount to state practice for the purpose of identifying the content of a legal rule; it is merely that different types of activity carry different weight. Both physical and verbal acts of States constitute practice that contributes to the creation of customary international law. Physical acts include, for example, battlefield behavior, the use of certain weapons and the treatment provided to different categories of persons. Verbal acts include military manuals, national legislation, national case-law, instructions to armed and security forces, military communiqués during war, diplomatic protests, opinions of official legal advisers, comments by governments on draft treaties, executive decisions and regulations, pleadings before international tribunals, statements in international organizations and at international conferences and government positions taken with respect to resolutions of international organizations.

Consistency of practice

One of the most important factors in the formation of customary law is that the state practice must be reasonably consistent. Customary international law results from the uniform and consistent conduct of states, undertaken with the conscious conviction on the part of states that they are acting in confirmation with law, or that they were required so to act by law.

Generality of practice

The practice must be significant to number of states. As the Anglo-Norwegian Fisheries Case and North Sea Continental Shelf Case illustrate, not all states need participate before a general practice can become law. In the Asylum Case, the court recognized that Art. 38 of the statue of the ICJ encompassed local custom as well as general custom in much the same way as it encompasses bilateral and multilateral treaties. Local customary law may exist where a practice has developed between two or more states, both or all of whom recognize the practice as binding.

Opinio Juris

It is not enough for the formation of customary law that there is general, uniform and consistent state practice. In order that this practice constitutes law, states must recognize it as binding upon them as law. Opinio juris relates to the need for the practice to be carried out as of right. The particular form in which the practice and this legal conviction needs to be expressed may well differ depending on whether the rule involved contains a prohibition, an obligation or merely a right to behave in a certain manner. Opinio juris plays an important role, however, in certain situations where the practice is ambiguous, in order to decide whether or not that practice counts towards the formation of custom. Opinio Juris is an essential element in the formation of customary law.


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