In This Article Expand or collapse the "in this article" section Monism and Dualism in International Law

  • Introduction
  • General Overviews
  • The Development of the Theories of Monism and Dualism

International Law Monism and Dualism in International Law
Madelaine Chiam
  • LAST REVIEWED: 27 June 2018
  • LAST MODIFIED: 27 June 2018
  • DOI: 10.1093/obo/9780199796953-0168


Monism and dualism were originally conceived as two opposing theorizations of the relationship between international law and domestic law. The subject of considerable debate in the first half of the 20th century, monism and dualism are regarded by many modern scholars as having limited explanatory power as theories because of their failure to capture how international law works within states in practice. Notwithstanding their decline as theories, monism and dualism retain power as analytical tools. They act as consistent starting points for examinations of the relationship between international and domestic law. For example, scholarship on the role of international law in domestic or European Union (EU) law, and on the ways that domestic courts incorporate international human rights law, continues to use monism and dualism as touchstones for analysis. A number of recent decisions in domestic courts have seen some scholars revive monism and dualism as potential ways to understand domestic judicial reasoning on international law. Monism and dualism also provide a shorthand way of signaling attitudes of individuals and institutions within domestic legal systems toward international law. In its most straightforward form, monism holds that international law and domestic law form part of a single universal legal system. Monism’s most famous proponent, Hans Kelsen, considered that there was a hierarchical relationship within the monist legal system, under which international law was superior to domestic law and thus prevailed in any conflict between the two laws. A dualist system treats the international and domestic systems of law as separate and independent. The validity of international law in a dualist domestic system is determined by a rule of domestic law authorizing the application of that international norm. Because of the variety of ways in which domestic systems incorporate international law, some scholars have preferred the term “pluralism” to “dualism.” There are multiple forms of both monism and dualism. Indeed, one of the main critiques of both theories is that no state’s system is strictly monist or dualist. Instead, international law may be treated in a variety of ways by the different institutions of a state. For example, courts may use international law in ways that a parliament does not. Or a state may allow for the direct incorporation of customary international law, but require international treaties to be transformed into domestic legislation before they can have direct effect within a state. The scholarship on monism and dualism can broadly be divided into two kinds: theoretical expositions on the concepts themselves and analyses that take monism and dualism as the departure point for critique, often combined with an exposition on the practice of international law within states. Almost all of the scholarship included in this bibliography falls within one of those two types.

General Overviews

It is conventional practice for international law textbooks and casebooks to include a chapter on the relationship between international and domestic law. Such chapters generally describe monism and dualism, position them as the traditional theoretical ways of understanding the relationship between international and domestic law, and then critique the concepts as unhelpful. Many chapters then propose other ways of conceiving the relationship between international and domestic law, often grounded in an account of the practice of states. Higgins 1994 and Malanczuk 1997 are especially insightful examples of this pattern, although some of the case law in their chapters is outdated in the early 21st century. O’Connell 1970 accepts the relevance of monism and dualism, while discussing two other ways in which the relationship can be conceived. Crawford 2012 and Denza 2006 provide more up-to-date case law and are arranged in an accessible manner. Ferrari-Bravo 1983 provides historical context for the development of monism and dualism. The edited collections Charlesworth, et al. 2005 and Nijmann and Nollkaemper 2007 aim for “new perspectives” on the relationship between international and domestic law, and their general discussions include modern reconceptions of monism and dualism.

  • Charlesworth, Hilary, Madelaine Chiam, Devika Hovell, and George Williams, eds. The Fluid State: International Law and National Legal Systems. Sydney, Australia: Federation Press, 2005.

    The editors view the orthodox accounts of monism and dualism as assuming fixed and rigid categories of interaction, and argue instead that the categories of “national,” “international,” and the “state” are fluid. The different chapters examine national contexts, including Australia, New Zealand, Canada, and China, with this fluidity as the guiding principle.

  • Crawford, James. Brownlie’s Principles of Public International Law. 8th ed. Oxford: Oxford University Press, 2012.

    DOI: 10.1093/he/9780199699698.001.0001

    A comprehensive overview, this chapter rejects the theoretical models, advocating instead a pluralist view of relations between international and national law. It provides an excellent introduction to international law’s approaches to national law, as well as international law in common law and civil law traditions.

  • Denza, Eileen. “The Relationship between International and National Law.” In International Law. 4th ed. Edited by Malcolm Evans, 412–440. Oxford: Oxford University Press, 2006.

    A good example of the modern approach to monism and dualism. Denza positions the theories as lacking useful explanatory power and focuses instead on specific questions about the relationship between international and national law. These include: “Is International Rule Directly Applicable and Directly Effective?” and “Can a Treaty Prevail over a National Constitutional Norm?” Accessible and practically oriented.

  • Ferrari-Bravo, Luigi. “International and Municipal Law: The Complementarity of Legal Systems.” In The Structure and Process of International Law. Edited by R. S. J. Macdonald and Douglas M. Johnston, 715–744. Dordrecht, The Netherlands: Martinus Nijhoff, 1983.

    An analysis of the applicability of the theories of monism and dualism, which the author calls pluralism, to the international problems of his period. Provides specific and useful historical context on the development of the two theories.

  • Higgins, Rosalyn. Problems and Process: International Law and How We Use It. Oxford: Clarendon Press, 1994.

    Argues that clashes between international and domestic law in domestic courts are “substantially conditioned” by whether the relevant state is more monist or dualist in approach. Higgins further counsels of the importance of “legal culture” to the reception of international law by domestic courts. An excellent introduction to the ways in which the concepts of monism and dualism continue to influence international legal thinking.

  • Malanczuk, Peter. Akehurst’s Modern Introduction to International Law. London: Routledge, 1997.

    Provides an excellent summary and extensive further reading on the rise and fall of the theories of monism and dualism, as well as an overview of the varied approaches of domestic legal systems of different states to international law. Useful and succinct.

  • Nijmann, Janne, and Andre Nollkaemper, eds. New Perspectives on the Divide between National and International Law. Oxford: Oxford University Press, 2007.

    The various authors examine the relationship between international and national law specifically in the context of globalization, the emergence of common values, and the dispersion of authority over different public and private actors. Monism and dualism are given different levels of emphasis in the various chapters (key contributions are described separately in this bibliography). A valuable contribution to the modern debate on the international/national law relationship.

  • O’Connell, D. P. International Law. Vol. 1. 2d ed. London: Stevens & Sons, 1970.

    Chapter 2 details four ways in which the relationship between international and national law can be conceptualized: monism, dualism, reverse monism, and harmonization. A classic treatment of the concepts.

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