This article is devoted to current practices concerning the application of general principles of law in the light of their function in the international legal system. As a means of the application and interpretation of both treaty and customary law, general principles of law perform a crucial function in the system of international law, which is understood as set of interrelated rules and principles – norms. The role played by general principles of law in the international legal order has been discussed by academia for years now. Initially they were used to ensure the completeness of the system of international law. However, at the current stage of development of international law, when many of them have been codified, they are usually invoked by international courts for the interpretation of treaties and customary law and/or the determination of their scope. This means that despite their ongoing codification they do not lose their character as general principles and are still applied by international courts in the process of judicial argumentation and the interpretation of other norms to which they are pertinent. References by international courts to general principles of law perform the allimportant function of maintaining the coherence of the international legal order, which is faced with the twin challenges of fragmentation and the proliferation of international courts.

There are different meanings and functions of what is called a “general principle of law.” This article seeks to address their importance as the basis for the systemic integration of the international legal order. When international law is considered as a legal system, its normative unity and completeness seems essential. This article argues that general principles of law are a necessary, although less visible, element of international legal practice and reasoning, which secure the systemic integration and long-lasting underpinnings of international law. In this sense they may be seen as the gentle guardians of international law as a legal system.

The present text describes the attitude toward sources of law in the recent works of the International Law Commission (ILC) on custom, general principles of law, and jus cogens (with special emphasis on reports of the respective special rapporteurs). The three main tasks of the text are to verify whether the ILC rapporteurs: grasped the essence of unwritten sources (reality-concern); preserved the coherence of views when referring to different topics (coherence-concern); and last but not least allow states to have the decisive voice as regards the set of their obligations (sovereignty-concern). The author notes the nominal strict attachment of the ILC to two-element nature of custom as a general practice recognized as law. Though in fact it should be a good message for states, this strict attitude of the ILC seems not to be based on a real stress test. It seems to ignore the reality of lawyers and even international judges referring to several customary norms without the slightest attempt to verify the true existence of both the two elements of custom – namely practice and opinio juris. What is more, the ILC does not see any problem with calling all general principles as sources of law. What is overlooked is the element of state consent to be bound by several presumed general principles. This is qualified by the author as a threat to state sovereignty – with states being pressured to follow some patterns of conduct to which they have not given their consent.