There are many valid international legal theories that can be analyzed in parallel to gain more knowledge regarding European integration, the relationship between the EU and national law and the issues faced by the EU, Member States and European citizens face due to the multitude of legal regimes.

International legal theories are useful in understanding law, society, decision-making processes and how communities and legal systems interact with each other. The theories of legal pluralism can be useful in assessing some aspects of the European integration that could help to further the interest of the EU, its Member States and European citizens.

Legal pluralism refuses the central monopoly of one legal system and emphasizes that during history and in contemporary times, there are many parallel legal orders, or layers of law, or binding norms from different sources. These theories do not view law and societies the classical way and redefine their relationship accordingly. They believe that different legal orders can coexist and interact at the same time.

The European Union is an interesting object to analyze from the point of view of legal pluralism and also the question of what is law, how many different layers of law interact and which one has higher authority can be an interesting question. The primacy of EU law, constitutional identity, European Union law taking over international law, state law and church law, etc. could all be interesting fields of research connected to these topics.

A particularly interesting concept regarding the interaction of different legal systems within the EU is the concept of Pier d’Argent regarding European Union law replacing international law and national law. The theory of international regional law states that EU law gradually takes over international law, as the Member States of the European Union have to apply international law in accordance with European Union law, but at the same time, a similar process is taking place where EU law replaces national law as well.

This is visible for example in the case of international organizations, where the EU represents its Member States (such as the WTO), or in case of European administrative law, which is applied by the administrations of the Member States.

However, legal pluralism does not support centralism and would rather favour different legal systems apply in a parallel manner. European Union law can coexist with national law and vice-versa and respect each other in case of collision. A pluralistic view of this phenomenon would be that an evolution towards a unified legal order is a false approach. Instead, it would emphasize that multiple legal orders may coexist, they have their own sources, authority, importance. What matters is striking the right balance between the different layers of law.

Law is established by human behaviour and the aspect of legal culture is particularly important for legal pluralists. There are different sociological groups, communities within the EU and the reason for the existence of different layers of law is precisely the legal culture of different communities, often intertwined with each other. Therefore, they all have their place and role to play within European integration.

The question is not who has the authority, the last word, but how these different legal systems and sets of norms can be balanced for the benefit of all of these communities, and in the end for the benefit of the EU, the Member States and European citizens. This could also enhance the legitimacy of the European Union through these different communities.

A criticism of legal pluralism could be that it also normalizes the underlying problems and does not allow for reconciliation, thereby obscuring the legal uncertainty stemming from these and slowing down the process of developing a common solution for years or even decades. Another problem is that if there are multiple authorities claiming their own law to be valid and having primacy, the uniform application of law comes into jeopardy.

Coexistence does not always mean balance and harmony. In the end, power will decide which legal system and set of norms will prevail. The European Union does not solve tensions between the intertwined legal orders, but manages and reproduces it continuously.

One thing is for sure: legal pluralism offers interesting perspectives on the analysis of the European integration, which can help further the European project itself as well.

Árpád Lapu is an assistant research fellow at the Károli Gáspár University of the Reformed Church in Hungary. He was a policy adviser on constitutional issues at the European Parliament between 2019-2024. He worked as an adviser at the Ministry of Justice of Hungary (2017-2019) and the Ministry of European Union Affairs (2024-2026), conducting EU law, international law and comparative constitutional analyses. He has earned his JD at the Pázmány Péter Catholic University in Hungary, has a BA in international relations from the University of Szeged, and an MA in European and international administration from Andrássy Gyula German Speaking University in Budapest. He has completed an LLM in international law at the Catholic University of Louvain (UCLouvain).