Customary Law

By Theodor Meron 

Together with treaties, customary law is one of the principal sources or components of international humanitarian law (IHL). It results from a general and consistent practice of States that is followed by them from a sense of legal obligation. The most obvious significance of a norm—a principle or rule—of a customary character is that it binds States that are not parties to the treaty in which the norm is restated. It is, of course, not the treaty provision, but the customary norm with identical content that binds such States. Customary law is important also for filling in matters inadequately covered by humanitarian law treaties. The fact that a norm is customary has also a significance for the applicable rules of interpretation and may have the beneficial effect of limiting the power of States to make reservations or to denounce those treaties of IHL which have a high customary law content. A State cannot opt out of its duty to conform to a general international law. The recognition that an IHL treaty states customary law strengthens the moral claim of the international community for its observance by emphasizing its moral character and deep roots in community values.

The decisions on customary humanitarian law of the Hague Tribunal for the former Yugoslavia are the linear successors to the decisions of the Nuremberg Tribunals. In both Nuremberg and The Hague, the tribunals looked primarily to the belief of States that certain principles are legally binding rather than to the practice of States in reaching their decisions. These decisions were supportive of an expansive view of customary law. Courts and tribunals tend to rely not on battlefield practice but on verbal statements in which States or institutions (for example, UN organs) express support for principles of IHL. Although they adhere to the traditional twin requirements (practice and the psychological belief that such practice is legally binding) for the formation of customary humanitarian law, in effect they weigh statements both as evidence of practice and as articulation of the psychological belief, which in the formation of humanitarian and human rights law is critical. The emphasis on the psychological element helps compensate for scarcity of supporting practice.

How to treat violations continues to be an important question. Both scholarly and judicial sources have shown reluctance to reject as customary norms—because of contrary practice—rules whose content merits customary law status, perhaps because of the recognition that humanitarian principles express basic community values and are essential for the preservation of public order. Even repeated violations are often not regarded as negations of customary law provided they are responded to by protests or condemnations by other States or international organizations, and that the State accused either denies the facts of its questionable conduct or appeals to exceptions or justifications contained in the rule itself.

There is considerable judicial and scholarly support, which is also endorsed by the International Committee of the Red Cross (ICRC), that the rules contained in the four Geneva Conventions of 1949 for the Protection of Victims of War and in the Hague Convention (IV) of 1907 on the Laws and Customs of War on Land (except for administrative, technical, and logistical provisions) reflect customary law. It is also widely recognized that many, perhaps even most, of the provisions, principles, and rules contained in Additional Protocol I to the Geneva Conventions and some, perhaps even many, of the provisions contained in Additional Protocol II reflect customary law. Several rules pertaining to types of weapons, and especially the prohibition on the use of chemical weapons, are regarded as customary.

A declaration of the significance of customary law is incorporated into several IHL treaties, most notably in the so-called Martens clause, named for its drafter, Feodor de Martens, the adviser to the Russian Foreign Ministry at the beginning of the century. First inserted in the preamble of the 1899 Hague Convention II, this provides a minimum threshold of humanitarian treatment by combatants even in the absence of specific treaty language. “Until a more complete code of the laws of war is issued, the High Contracting Parties think it right to declare that in cases not included in the Regulations adopted by them, populations and belligerents remain under the protection and the empire of the principles of international law, as they result from the usages established between civilized nations, from the laws of humanity, and the requirements of the public conscience.”

The Rome Statute of the International Criminal Court codifies many rules and principles of IHL as customary criminal law.

In any discussion of customary law, sight must not be lost of the fact that the Geneva Conventions have attained practically universal ratification and that the Additional Protocols have gained many ratifications. For States parties to the IHL treaties, all treaty provisions, no matter whether they reflect customary law or not, are of course binding. In the national law of many countries, however, customary law is a part of the law of the land. As such, it may be invoked by victims of violations of IHL or human rights law.

Related posts:

  1. Customary Law: The ICRC Study
  2. Crimes against Peace