Treaties and Customary International Law: A Comprehensive Guide
Treaties
Sources:
Treaties may be defined as follows: “[A treaty] is generally an international agreement between States, governed by international law and intended to produce legal effects.” (Memory)
Insights from the Concept:
- Treaties are usually held between States, but there are also treaties between States and other subjects of international law (e.g., the Holy See or the United Nations) or between such other subjects (e.g., two international organizations).
- For an agreement to constitute a treaty, it should be governed by international law. A treaty is not an agreement subject to a particular national law (e.g., a sale of a nuclear reactor which stipulates that the agreement shall be governed by the internal law of the seller).
- The treaty must be intended to produce legal effects, to establish rules of law, to create, modify, and extinguish rights and obligations, and to recognize a situation that no party may later controvert.
- The various names for treaties in practice are used interchangeably: conventions, agreements, charters, protocols, etc.
Classification of Treaties:
A treaty can be:
- Bilateral: Treaties concluded between only two States.
- Multilateral or Group: Treaties concluded between a number of States, such as the Geneva Conventions on the Law of the Sea.
Treaties can also be distinguished as:
- Treaty-Contract: Imposes on each of the contracting parties a single act or supply, as in a treaty ceding territory in exchange for compensation.
- Treaty-Law: Governs the behavior of the contracting States on a permanent and continuous basis, e.g., the UN Charter, the UN Convention on the Law of the Sea, and so on.
Furthermore:
- General Treaties: Fully regulate a particular subject, such as the UN Convention on the Law of the Sea.
- Special Treaties: Regulate certain specified subject matter, such as the capture of swordfish in the South Pacific.
There are treaties classified according to their governing matters, such as treaties in the economic sphere (e.g., MERCOSUR free trade treaties, the European Union), treaties classified according to their specialty (e.g., the North Atlantic Treaty), and treaties that concern the delimitation of frontiers.
Customary International Law
According to the prevailing doctrine, customary international law involves the concurrence of two elements:
- State Practice: A practice of States formed by the constant repetition of acts in the same direction, acting as precedents.
- Opinio Juris: The conviction by States that when performing these acts, they are carrying out a legal obligation. This is also known as the opinio juris sive necessitatis.
If a customary rule is universal (i.e., applicable to all States), it is also necessary that it has been accepted by the entire international community, particularly the States interested in the matter. It is not required that the State against which a customary rule is invoked gave its acceptance, recognition, or assent. General acceptance is sufficient. However, a customary rule is unenforceable against a State that, during the formation of a rule and before it crystallized, refused to accept it.
It is not necessary that the practice constituting a custom continues for a long time, nor that the practice is immemorial. Even a practice for a short period may result in establishing a customary rule. For example, the rule that every State has exclusive sovereignty over the airspace above its territory and the rule establishing the character of res nullius of outer space were formed in a short time.
The precedents that form the material element of custom are acts or abstentions by States reflecting international law, such as diplomatic correspondence, instructions to diplomats and consular officials, statements or attitudes at international conferences, etc.
The essential element of custom is opinio juris. This distinguishes customary rules from mere usages, which are followed only out of courtesy, expediency, or tradition, and not because States feel legally bound to observe them. An example of such usage is the ceremony of salutes between warships.
Opinio juris can be difficult to prove and must be determined on a case-by-case basis in light of all the circumstances surrounding the acts intended to reflect it.
Customary rules are often slow and imprecise in their formation and content. For this reason, in some areas, they tend to be superseded by explicit rules. However, new treaties or conventions do not fully displace customary rules. Instead, they fill the silences of treaties, serve to interpret their provisions, and act as rules of conduct for States that are not parties to them.