Taking the Two-Elements Theory of International Customary Law Seriously - Problems with Double Counting
Among the few other preconditions of customary law F. Savigny mentions the "undertaking of the act in the feeling of a legal necessity (opinio necessitatis)" . As K. Wolfke explained, the two-element theory of customary law (according to which there are two constituent elements, i.e. practice and opinio iuris) was introduced to the modern theory of law by the historical school of law. The purpose of this concept was a departure from well-established understanding of the customary law as a tacit consensus populi. According to the generally agreed approach, international customary law is composed of an objective element, i.e. practice and the subjective element - so-called "opinio iuris". This last one is usually understood as a feeling of doing one's duty or simply doing what is right. Practice without opinio iuris is simply a "usage". Alternatively, it can be a kind of international courtesy or protocol, which are loosely relevant for international law. The ICJ in the judgment in the case of North See Continental Shelf considered the premise of opinio iuris "the most important of all". It is the differentia specifica of the customary law. Opinio iuris resembles tacit consent at least in one: both are opposite to usage. (original abstract)
- Aust A., Modern Treaty Law and Practice (2007).
- Goldsmith J.L., Posner E.A., Understanding the Resemblance Between Modern and Traditional Customary International Law, (2000) 40, "Virginia Journal of International Law", 645.
- Hart H.L.A., Concept of law (1961).
- Jennings R., Watts A., Oppenheim 's International Law - Volume 1 - Peace - Introduction and Part I (1996).
- Kelsen H., The Pure Theory of Law (1967).
- Koskienniemi M., From Apology to Utopia - Structure of International Legal Argument (2007).
- Kwiecień R., Teoria i filozofia prawa międzynarodowego - Problemy wybrane (2011).
- Lauterpacht H., The Nature of International Law and General Jurisprudence, (1932) 37, "Economica" 315.
- Lefkowitz D., The Source of International Law: Some Philosophical Reflections, in S. Besson, J. Tasioulas (eds) The Philosophy of International Law (2010) 200.
- Lepard B.D., Customary International Law - A New Theory with Practical Applications (2010).
- Mendelson M., The International Court of Justice and the sources of international law, in Fifty years of the International Court of Justice (1996).
- Nolte G., Report 3. Subsequent Agreement and Subsequent Practice of States Outside of Judicial or Quasi-judicial Proceedings, in G. Nolte (ed), Treaties and Subsequent Practice (2013) 350.
- Orakhelashvili A., The Interpretation of Acts and Rules in Public International Law (2008).
- Postema G.J. Custom in international law: a normative practice account' in A. Perreau-Saussine, J.B. Murphy (eds) The Nature of Customary Law - Legal Historical and Philosophical Perspectives (2007) 296.
- Sadler G.T., The Relation Custom to Law (1919).
- Savigny F.C., System of the Modern Roman Law (1867).
- Shapiro S.J., What is the Internal Point of View?,(2006) 75 "Fordham Law Review" 1162.
- Slama J.L., Opinio Juris in Customary International Law, (1990) 15 "Oklahoma City University Law Review" 648.
- Walden R.M., Customary International Law: a Jurisprudential Analysis, (1978) 13, "Israel Law Review" 97.
- Waldron J., Law and Disagreement (2004).
- Wolfke K., Custom in Present International Law (2nd ed 1993).