The Restatement also identifies the sources of international law: custom, international agreement, “general principles common to the major legal systems of the world.”6 While treaties and custom are primary sources, general principles are supplementary rules.
Customary law comprises the “general and consistent” practice of states followed from a sense of legal obligation. Such practice may include diplomatic acts, official policy statements, and other governmental acts. Until recently, international law was mostly customary law, with agreements being limited to particular arrangements between states, but rarely used for general law-making. Although customary law evolves from the practice of states, for such practice to become a rule of law states must abide by the conduct out of a sense of legal obligation —opinion juris sive necessitatis. A practice that states follow but have no sense of obligation to do so does not constitute a customary norm.
The practice of states can be found in both what states say and what they do (commission) or fail to do (omission) under circumstances in which failure to act may indicate acceptance of the acts of another state that have an impact on another state’s legal rights. In addition, for state practice to become customary law, the state practice must be general and consistent over time, with no major alterations or deviations. Significantly, although the general, consistent practice of states results in a binding customary norm, such principles may not be binding on states that are “persistent objectors” (i.e., states that during the development of the norm object to it).7
Two observations are appropriate regarding custom and persistent-objector status. One, a state cannot be insulated, as a persistent objector, from being bound by a peremptory norm (jus cogens) as such norms hold a superior status and permit no derogation.8 Significant for this project is that not all customary human rights norms are jus cogens—the prohibitions against genocide; slavery and the slave trade; causing disappearances of persons; torture and cruel, inhuman, and degrading treatment; prolonged arbitrary detention; and systematic racial discrimination constitute peremptory norms.9 Two, a new state coming into the international legal world will be bound by existing custom, without the opportunity to become a persistent objector. That status is only available to states in existence at the time that the norm is being created. This reality has subjected customary international norms to criticism by newly emerging states that are bound by existing rules although they had no part in their development and are given no opportunity to opt out of their application. In Article I, § 8, the U.S. Constitution refers to the “law of nations,” and U.S. Supreme Court case law has made clear that customary law is part of U.S. law.10
Treaties, the first listed source in Article 38 of the Statute of the ICJ, are very significant in the international realm and are, in modern times, the most frequently used tool for international law-making. Whereas custom is grounded in the practice of states, treaties are rooted in the consent of states. It is important to observe that the requisite technicalities for a document to be labeled a treaty are different in the international realm and under U.S. constitutional law, although one instrument may satisfy the requirements of both. Thus, what is properly called a treaty in international law may or may not qualify as a treaty under the U.S. domestic system.
In the international realm, the Vienna Convention on the Law of Treaties is the principal source of the law of treaties. At Article 2(1)(a), it defines a “treaty” as “an international agreement concluded between States in written form and governed by international law, whether embodied in a single instrument or in two or more related instruments and whatever its particular designation.” Article II, § 2, of the U.S. Constitution provides that “the President … shall have Power, by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur.” Thus, under the Constitution, an international agreement, concluded by the United States with another nation, in written form, and governed by international law—factors sufficient to make the instrument a treaty pursuant to the Vienna Convention requirements—is not a “treaty” in the domestic sense unless two-thirds of the Senate gives its advice and consent to the document. We will further address treaties and U.S. law later in the chapter, but first we need further to develop the concept of treaties in the international realm.
In the international sphere, in order to decide what constitutes an “international agreement,” one must first analyze the text. Ultimately, whether an instrument is a treaty depends on the intent of the parties. Thus, when there is doubt as to whether an instrument is a treaty, one analyzes the negotiating history, the formalities observed, and the expectations induced. The more formal the process, and the more formal the law-making authority of the government involved, the stronger the case for finding an “agreement.”
Treaties share critical characteristics as parliamentary and contractual instruments. For example, in terms of “who” can enter into a treaty, treaties are similar to domestic laws because only sovereigns can make treaties. On the other hand, like contracts, treaties apply only to those who are signatories.
Having first defined treaties and then described some basic characteristics, it is important to turn to the rules applicable to treaties that are set out in the Vienna Convention. The Convention is considered a codification of existing customary law.11 Therefore, non-signatories may be bound to its terms. For example, the United States has signed, but the Senate has not given its advice and consent to, the Vienna Convention. Yet the U.S. State Department has acknowledged that the United States is bound to its terms as they reflect binding customary norms.12
Because this is a volume on trade and human rights, it is important to emphasize that the Vienna Convention’s definition of treaty limits those instruments to written agreements concluded between states. This definition excludes agreements between a state and a private entity, although, through interpretation, the definition has been modified in practice to include agreements between a state and an international organization because such organizations are considered subjects of international law. In all cases, it is only the trade compacts concluded between and among states that qualify as treaties.
It is also important to note at this juncture that not all agreements between states are necessarily treaties. To be treaties, the agreements must be governed by international law. Thus, an agreement between State A and State B for the purchase by State A of State B’s beef using a standard form contract of the meat trade will not be deemed a treaty. Similarly, the purchase of a building or a piece of land by a state, when the contract is subject to the law of the municipality or a third state, will not be deemed a treaty.
1.3 International Law-Making: Specific Provisions
Let us now turn to some provisions of the Vienna Convention to ascertain what determines whether an instrument is a “treaty.” Part II of the Convention lays out the requirements for the “Conclusion and Entry into Force of Treaties” with Section 1 addressing the conclusion of treaties and Section 2 addressing reservations.
Regarding conclusion of treaties, Article 6 of the Vienna Convention provides that all states have the capacity to enter into a treaty. To be a state in international law, an entity must satisfy four requirements: it must have (a) defined territory; (b) permanent population; (c) a government capable of controlling the territory; and (d) a government with the ability to enter into international relations.13 One significant article in the first section of the Convention is Article 18, which imposes on signatories an obligation not to act in a way that “would defeat the object and purpose of a treaty.”
Section 2, “Reservations,” articulates an important concept in treaty-making. Reservations are “unilateral statement[s] … made by a state, when signing, ratifying, accepting, approving or acceding to a treaty, whereby it purports to exclude or to modify the legal effect of certain provisions of the treaty in their application to that State” (art. 2(d)). Thus, reservations allow states unilaterally to modify the terms of a treaty or the legal effect of the terms of a treaty. However, the Vienna Convention prohibits reservations that are “incompatible with the object and purpose of the treaty” (art. 19(c)). To ascertain incompatibility, the analysis scrutinizes the reservation in light of the purpose of the treaty. Reservations that