This article discusses the classical question whether general principles of law form a separate source of international law. To this end it adopts the method of a posteriori analysis, examining the normative nature of various principles of law one by one. This analysis leads to the conclusion that only some principles have a normative nature, while others lack it.

International law reflects systemic conditions compatible with its essence, which means that a space must exist inside the borders of that order for the presence of the phenomenon of general principles. The assumption that international law is a legal system ipso facto means that general principles must exist within its borders. A general principle of law is a necessary element of every legal order. It is a form and a tool in which the efforts of the individual seeking to comprehend a given phenomenon are materialized through imposing order on it rather than by breaking it down into unconnected and independent elements. Since law is an expression of order, law therefore applies general principles. The systematicity of law, and therefore of international law as well, creates the primary source of the binding force of any norm. Considerations of natural law or positive law justifications for the presence of general principles in international law are of little consequence, as the source of general principles is the systemic nature of the law. Order and hierarchy are part of the rationalized system in which norms of law present themselves. This dependency applies also to norms of international law. The role of the judge is to fill in the appropriate normative content (general principles) in fields constituting at one and the same time both a necessary element and a consequence of the systemic character of the international legal order. Within this context the principle of good faith constitutes one of the bases for considerations concerning the extent of the international legal order. The extent of international law reaches as far as the extent to which evidence of good faith are present among the subjects of international law. The impossibility of describing relations between two states by the use of the determinants of good faith, translated in turn into a normative general principle, determinates the limits of international law.

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.