It would be difficult to overstate the profoundly important role played by the concept of customary international law in the international legal system. In contrast to treaty law, customary international law is universally binding on all states. It thus constitutes the substratum of common legal rights and obligations of the entire community of states, upon which their more particularized legal relationships (usually in the form of treaties) are built. What is more, customary international law is an enormously powerful normative concept in that it can have the effect, under certain circumstances, of binding states which have not actually consented to its content at all. It thus challenges positivist interpretations of the theory of consent. At the same time, it receives universal endorsement as a valid and binding source of international law. Textbook, chapter five.

The following questions could help you in articulating your argument in the intended essay.

If customary international law is not written, it means that many states may have not been involved in its creation. So why is this law universally binding?

Given the positivistic nature of traditional international law, how are states that have not consented to customary international law bound by it? Indeed, what makes customary law universally binding?

Article 38 of the ICJ Statute ranks customary international law as the second source of international law. Why then, does customary contravene the consent of states?

If customary law is a normative concept, does it mean that all norms practiced by states in the modern time contributed to this kind of law?

Provide the key references