Dualism

Dualism denies that international law and national law operate in the same sphere, although it does accept that they deal with the same subject matter. For dualists, such as Triepel, international law regulates the relations between states whereas national law regulates the rights and obligations of individuals within states. International law deals with that subject matter on the international plane whereas national law deals with the subject matter internally. Consequently, if an individual is denied a right in a national court which is guaranteed under international law, the national court will apply the national law. Likewise, action by a state that might be unlawful under international law may nevertheless attract validity and protection in national law if there is a clear rule of national law to that effect […]. The state itself may be in breach of its obligations on the international plane, but that is a matter for an international court. There are, in other words, dual legal systems operating simultaneously in respect of the same rights and obligations and the national court should not concern itself 'with the meaning of an international instrument operating purely on the plane of international law' - per Simon Brown LJ in Campaign for Nuclear Disarmament v Prime Minister of the United Kingdom [2002] EWHC 2777 (QB). The effect of such a doctrine is that a government may be behaving perfectly lawfully within its own territory, even though its conduct may entail international responsibility. […] For the present, however, the impact of the dualist theory is that international law cannot invalidate domestic law, or vice versa, and rights and obligations arising under one system cannot automatically be transferred to the other. This theory does accept that the systems can come into conflict - because they deal with the same subject matter - but recognises that each system applies its own law unless the rules of that system say otherwise. International courts apply international law and national courts apply national law.

Different subject matter

Both monism and dualism accept that international law and national law deal with the same subject matter; that they are in fact concerned with the same substantive matters. Monism simply accepts that the international rule takes priority, whereas dualism insists that each system deals with the matter in its own way. A third view, promoted by Fitzmaurice and Anzilotti, denies that international law and national law ever operate in the same sphere or that they are concerned with the same subject matter. According to this view, the relationship between international law and national law is like the relationship between English law and French law, they never contradict each other as systems of law. It may be that the 'obligations' of each system come into conflict - as where national law allows imprisonment without trial and international law does not - but then which obligation is to prevail is to be settled by the 'conflict of laws' rules of the particular court. So, rules of national law may or may not say that international law is to prevail, but the solution is still dictated by national law.

Essentially, this is a less theoretical approach to the problem of the relationship of international and national law. Each system of law is seen as completely independent of the other because it is argued that this is how the systems relate in practice. If obligations do conflict, national courts give effect to national law obligations, unless a national rule says otherwise, and international law gives effect to international obligations, unless an international rule says otherwise. It will be appreciated that in this regard the third approach is similar to the dualist theory, and in terms of practical consequences there is little difference between the two. The distinction lies primarily in the theoretical point that this is a theory of 'coordination' (the two systems do not conflict as systems), whereas both monism and dualism are theories of 'confrontation'.

These theories have occupied the minds of legal philosophers ever since international law emerged as a coherent body of rules that could affect national legal systems. […]