After the first week of the LL.M. Program here at Stockholm University I've had an interesting discussion together with the lecturer and one of my dear colleagues about monism and dualism within Public International Law (and of course European Law).
After some research for this topic here is my conclusion.
Professor Heribert Franz Köck who tought at Johannes Kepler University in Linz Austria starts his introduction of this issue qoutes Alfred Verdross who speaks about an entity of law which devided into national and international law. Now it is up to the subject, the state, itself to decide whether to devide this entity or not.
Starting with dualism, this view manifests that there is a complete distinction between national and international law. It argues with the different approaches of law making and the different fields both are trying to regulate. A conflict between those two is therefore impossible. (Just as Stadlmeier in his explanation).
The monistic view however has a different approach and sees and entity of law even though there are different means of creating a law as such and it does not deny that there might be different adressees for a specific provision. Whereas in public international law mostly its subject are effected (exeption e.g. human rights law) national law has mostly a direct approach towarts natural persons. The huge difference compared to dualism is, that it points out that often natioanl matters can be influenced by international law as well. Thus a conflict is possible.
This theory gives premacy to norms set up through international law. Whereas a radical view of monism annuls the natioanl provision in favour of the international one, the smoother view sets up a lesser harsh approach.
As an example Germany's Art. 25 of the constitution gives premacy to public international law stating that they are part of the law and have priority over national law. Austria follows the same approach in its constitution under Art. 9 ( in connection with Art. 49), but without giving priority to one of those legal fields. The Constitutional Court however decided in the "Vermögensvertrag Polen"-Case in favour of Public International Law.
However the transformation of international law is a different story whether there is need for such an action or not. Thus it is possible that on the material side international law is used but formally as a national provision.
Additionally to come to the core of the discussion is the missing willingness of national courts to take on international provision often because of missing knowledge or simply because they refuse to use the given "foreign" provisions. This is does also not have an influence of the question whether a state runs a dualistic or monistic system.
Finally to conclude this discussion it is to say that basically the monist system takes over the dualistic view as international law has become more important (not at least because of the Vienna Convention on the Law of the Treaties, but also because of other factors) and took over a lot of other fields such as the Criminal Law sector. Just compare the provision stated in the ICCPR or the ECHR with the national penal codes of parties to these treaties. Furthermore especially treaty law as a source of international law can and does have an impact on the citizens and other legal persons of state. Thus comparing the discussed approaches questions the efficiency and existence of dualism in general.
Heribert Franz Köck - Völkerrecht
Sigmar Stadlmeier - Völkerrecht I