Ascertainment of the law on any given point in domestic legal orders is not usually too difficult a process. In the English legal system, for example, one looks to see whether the matter is covered by an Act of Parliament (or possibly a statutory instrument) and, if it is, the law reports are consulted as to how it has been interpreted by the courts. If the particular point is not specifically referred to in a statute, court cases will be examined to elicit the required information. In other words, there is a definite method of discovering what the law is. In addition to verifying the contents of the rules, this method also demonstrates how the law is created, namely, by parliamentary legislation or judicial case-law. This gives a degree of certainty to the legal process because one is able to tell when a proposition has become law and the necessary mechanism to resolve any disputes about the law is evident. It reflects the hierarchical character of a national legal order with its gradations of authority imparting to the law a large measure of stability and predictability.
The contrast is very striking when one considers the situation in international law. The lack of a legislature, executive and structure of courts within international law has been noted and the effects of this will become clearer as one proceeds. There is no single body able to create laws internationally binding upon everyone, nor a proper system of courts with comprehensive and compulsory jurisdiction to interpret and extend the law. One is therefore faced with the problem of discovering where the law is to be found and how one can tell whether a particular proposition amounts to a legal rule. This perplexity is reinforced because of the anarchic nature of world affairs and the clash of competing sovereignties. Nevertheless, international law does exist and is ascertainable. There are ‘sources’ available from which the rules may be extracted and analysed.
By ‘sources’ one means those provisions operating within the legal system on a technical level, and such ultimate sources as reason or morality are excluded, as are more functional sources such as libraries and journals. What is intended is a survey of the process whereby rules of international law emerge.