What is the relationship between customs and treaties? Considering that these are the most important sources of international law
Customs and treaties are both important sources of international law, but they differ in their nature and formation.
Customs refer to the consistent patterns of behavior and practices followed by states over time. They arise from the general and consistent practice of states, which they follow out of a sense of legal obligation (known as opinio juris). Customary international law is formed when the required elements of state practice and opinio juris are met. It is important to note that customary international law can still evolve and change over time as state practices and opinions adapt.
On the other hand, treaties are formal written agreements between states that establish obligations and rights. Treaties can be bilateral (between two states) or multilateral (involving multiple states or international organizations). Treaties are usually negotiated and concluded by states through a series of diplomatic negotiations and consent, expressed through signing, ratification, or accession.
The relationship between customs and treaties is often complementary. Customary international law can serve as the foundation for treaties, providing principles and norms that shape the content of the agreements. Treaties, once ratified, become binding international obligations on the states that are party to them. They can also contribute to the development of customary law by influencing state practice and opinio juris.
In cases where there is a conflict between a customary rule and a treaty provision, the principle of lex specialis (special law) comes into play. Lex specialis states that when two normative rules apply to the same situation, the more specific rule prevails over the more general rule. Therefore, the specific provisions of a treaty will generally take precedence over conflicting customary rules.
In summary, customs and treaties are both important sources of international law. Customs emerge from the consistent practice and opinio juris of states, while treaties are formal written agreements negotiated and ratified by states. They can influence and complement each other, but treaties, being more specific and formal, generally take precedence over conflicting customary rules through the principle of lex specialis.