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Sources of International Law
The starting point is Article 38(1) of the Statute of the International Court of Justice, 1945:
'The Court, whose function is to decide in accordance with international law such disputes as are submitted to it shall apply:
a) international conventions, whether general or particular, establishing rules expressly recognised by the contesting States;
b) international custom, as evidence of a general practice accepted as law;
c) the general principles of law recognised by civilised nations;
d) subject to the provisions of Article 59, judicial decisions and the teachings of the most highly qualified publicists of the various nations, as subsidiary means for the determination of the rules of law."
But this does not provide a complete list of the sources of international law — it is a direction to the
Court authorising it to consider various materials when deciding disputes. GA resolutions, acts of international organisations, diplomatic correspondence etc. often influence the Court's decisions,
but are not listed as sources. The reason for this may be that they are not formally accepted sources of international law per se, but are evidence of state practice which may be submused under customary international law.
A distinction is sometimes made between formal, material and evidentiary sources of international law. Formal sources are those that explain the procedures by which rules become legally binding, for example, in the UK, the passage of Bill through Parliament is a formal source of law; in international law the formation of custom/Treaty is a formal source of law. Material sources,
on the other hand, are concerned with the content of the obligation, and perform the function of enabling subjects of international law to be reasonably certain about rights and obligations prescribed by the law. Examples are state practice, judicial decisions, GA resolutions, etc. —
because they all indicate what a state's obligations actually are, rather than the method by which those obligations become legally binding. Finally, an evidentiary source includes the precise content of legal obligations that bind the states, and are substance related. Things that form evidence of state practice, for example, can be diplomatic correspondence, actual state activity, etc. I don't think this is a very useful categorisation. Dixon also says that this distinction 'distorts the function of the sources of international law because all 'sources' are, in some way, both law creating and law identifying…' (see page 27).
Let's look at the individual categories of the sources of international law. These are:
- General principles of law;
and those not included in the statute:
- Judicial decisions
- Resolutions of international organisations? (see Higgins)
- Soft law 1) Custom = state practice + opinio juris
Law evolved from the practice/customs of states. The activities of states in the international arena may give rise to binding law. Eg: if all maritime nations declare territorial sea 12 miles seaward from the coastline, a customary law to this effect may develop. Some factors that can be identified as elements of customary international law, such as the consistency, generality and duration of state practice, as well as opinio juris.
State practice must be reasonably consistent. In the Lotus Case, the Permanent Court said that it must be 'constant and uniform'. However, the more fundamental the customary rule, the more consistent any contrary state practice must be before a change in that rule could be recognised (for example, alleged change to jus cogens should be supported by almost universal state practice). So the degree of consistency required will change depending on the subject matter.
State practice must be general, or in other words, common to a significant number of states.
However, special weight may be given to the practice of those states whose interests are specifically affected by the subject matter of the rule, such as the maritime states in the North Sea Continental
Shelf Cases. On the other hand, if a state initially and sustainably objects to a customary rule, this may prevent that state from being bound from it (the persistent objector): the Court in the AngloNorwegian Fisheries Cases said that Norway's persistent objection to any attempt to apply the tenmile rule to the Norwegian coast had rendered customary law to that effect inapplicable to Norway.
This was because there was an initial objection by a Norwegian minister in his statement, and sustained objection, following principles of delimitation that it considered part of its system in a consistent and uninterrupted manner. Furthermore, the 'general tolerance' of other States with regard to Norway's practice showed that such objection on Norway's part was not contrary to international law. (NB: in this case, the Court did not think that the 10-mile rule had acquired customary law status, but considered the above questions anyway).
This is important as it may later have effect on the practice of other states (acquiescing in deviation from the customary law); if deviations become so widespread, the previous rule will be destroyed and replaced.
In the Asylum case (Colombia v Peru), the Court recognised that local or regional custom could be binding among a group of states, though did not find that such existed on the facts. In that case,
the Colombian government had invoked 'American international law in general', alleging local custom peculiar to Latin American states. The party alleging the existence of local custom must prove constant and uniform practice within the locality, which Colombia could not in this case: 'the facts disclose so much uncertainty and contradiction, fluctuation and discrepancy in the exercise of asylum and official views expressed'.
General, uniform and consistent state practice must be supplemented by opinio juris — states'
recognition that the rule is binding upon them as law, a belief that the practice is obligatory. It is obviously difficult to ascertain whether there is opinio juris or not, as states rarely explicitly state
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