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Sovereignty referendums: Common legal and political issues.

Published: 22 September 2021

In this blog post, Ilker Gokhan Sen - visiting researcher at the University of Bergen Faculty of Law and an alumnus of the 2021 Centre on Constitutional Change Summer School - examines the common legal and political issues around sovereignty referendums.

The concept

Sovereignty referendums are popular consultations pertaining to territorial modifications, the independence of states, the self-determination of a decentralised community or adhesion of a state to a supra-national organisation. From a legal point of view, these referendums are matters of both international and constitutional law. From a constitutional point of view, there should first exist a political unit before adopting its constitution. Thus, all sovereignty referendums are inherently constitutional referendums. As regards the international law, sovereignty referendums entail the question of international personality, of a polity: the capacity to be the possessor of rights and duties under international law. Contemporary practice of sovereignty referendums may be categorised into three groups:

Independence, decolonisation (status), and transfer of sovereignty.

Independence referendums

Referendums held for the approval of secession of a territory for the creation of a new state are called independence referendums. Three sub-types may be distinguished.

The first type of referendums concerns the territories that are subject to the international law on decolonisation. East Timor (1999) and the referendum in New Caledonia (2020) may be included in this category. 

The second type of referendums include those that are held to approve a secession of a territory, to which international law does not explicitly bestow that right. The formal-legal basis is then provided by the agreement of the main actors. The referendum held during the accession of Montenegro to independence (2006), the one that led to the independence of South Sudan (2011), and the independence referendum in Scotland (2014) are the most significant examples.

The third type of independence referendums include those unilaterally held by secessionist groups or territories. Examples include the referendums held in Quebec (1980 and 1995) in its attempt to secede from Canada and the Catalan independence referendum of 2017.

Status referendums

The status referendums are held within a decolonisation context when independence is not an option (series of referendums held in the French overseas department of Mayotte), or is highly unlikely politically (Puerto Rico, 2020). In most of these referendums, a set of constitutional arrangements or an international treaty is submitted to the voters, in order to determine the relationship between the territories subject to decolonisation law and their administering states.

Transfer of sovereignty referendums

Transfer of sovereignty referendums may be either supra-national or sub-national. Referendums held in several European countries during the process of EU integration may be seen as major examples. The 2016 Brexit referendum added the “disintegration” aspect to that category. The subject of a sub-national referendum may be the creation of a constitutionally autonomous territory or revision of its constitutional status in a unitary state.

This category comprises the referendums on devolution in the UK.

Common issues

A rich historical data from international law and comparative constitutional law, offer an opportunity for a synthetic framework for a legitimate referendum. This may be summarised as follows.

De jure or de facto 

Ideally, referendums should take place, with valid legal base and/or with formal acceptance of all parties to the sovereignty conflict. The political/constitutional outcome of de facto independence referendums may differ depending on the context. In the Quebec case, Federal Supreme Court of Canada conferred referendums with a significant legal value: Despite having been held unilaterally by the Quebec Government, the Supreme Court of Canada opined that the referendum could have been a legitimate way to demonstrate the wish of the population to secede, and as the initiator of a negotiation process, which could result in secession.

In contrast, Spanish central government’s reaction to the Catalan referendum was not that benign. Constitutional Court of Spain has suspended the relevant referendum law passed by the Catalan parliament. Consequently, a region-wide police operation (Operation Anubis) took place in the run up to the referendum; and the Supreme Court sentenced the separatist leaders, for sedition, from nine to thirteen years of prison.

Qualified majority

When it comes to the sovereignty referendums, a qualified majority as a condition for approval looks like a legitimate measure. Given the importance of such referendums in a given polity, this condition may provide a more inclusive way of decision taking and help to avoid the stark majoritarian nature of the referendum device.

It is thus, a common feature in the constitutions of many democratic states; and quite a steady tendency in international law.

Voter qualification

The decision about entitlement to vote in sovereignty referendums entails two equally legitimate principles, which may, in most cases, be at odds with each other: universal suffrage and right to self-determination. Historical practice and law of sovereignty referendums use two criteria to reconcile conflicting rights and principles: nativity and residence.

In East Timor referendum for example, persons born outside of the territory but having at least one East Timorese parent, were entitled to vote. Yet this was not always the case. In the Brexit referendum, the UK High Court upheld a 15-year limit of absence for the British citizens’ right to vote, who lived abroad. The difference is mostly due to the pre-referendum history. When the political context is stable and peaceful before and during the referendum, it appears that the residency criterion outweighs the ethnic or birth criterion.

Designation of the voting units

The main question here is whether a given polity or territory should be treated as a single entity or be divided into more than one zones.

An illustrative example may be the 2004 Cyprus unification referendum. Here, two simultaneous referendums were held since international law recognised two distinct ethnic groups (Greek and Turkish). Consequently, the relevant international legal sources required a majority of the voters within each community for the referendum to be valid. This approach, however, did not find a support during the Brexit referendum. In that case, “the devolved regions argued that the UK included at least four demoi: those of Scotland, Wales and Northern Ireland, as well as England.

But this argument did not receive any support from the Westminister.

Formulation of the ballot question

Finally, the ballot question should be formulated to offer voters an informed and coherent choice. Firstly, the wording should be clear and free of ambiguity and should not be deceptive or confusing.Secondly, the universal democratic values also impose that the ballot should observe the rule of unity of content: the voters should not be forced to vote on more than one option disparately included in the same ballot question.



For more information see İlker Gökhan Şen, Sovereignty Referendums in International and Constitutional Law, Springer, 2015.

Also from the same author:  

“Referendums and Democratic Constitutionalism: Is There a Way for a Reconciliation?” in Populism and Democracy, Eds: Sascha HardtAalt Willem HeringaHoai-Thu Nguyen, Eleven Publishing, 2020”;    

“Sovereignty Referendums: People Concerned and People Entitled to Vote in The Routledge Handbook to Referendums and Direct Democracy Eds.: Laurence Morel and Matt Qvortrup, Routledge, 2018.


Ilker Gokhan Sen is a Visiting researcher at the University of Bergen Faculty of Law and an alumnus of the 2021 Centre on Constitutional Change Summer School. His research focuses on Direct Democracy, Comparative Constitutional Law,  and Populist Constitutionalism.

Photo by Elliott Stallion on Unsplash.

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