Europe faces a growing constitutional paradox. Many of the challenges that increasingly determine its future, including security, technological competitiveness, energy resilience, climate adaptation, financial stability, and strategic autonomy, are European in scale. Yet democratic legitimacy remains rooted primarily in national political communities.

The origins of this challenge became visible during the Euro Crisis. Member states retained fiscal sovereignty, yet excessive borrowing by one country could create substantial risks for others. National fiscal decisions generated cross-border liabilities without corresponding cross-border democratic representation. Countries potentially exposed to the consequences of fiscal imprudence often lacked any meaningful voice in the decisions that created such risks.

The traditional debate on European integration offers two responses. One is federation: the transfer of substantial authority to a European political centre and the development of a common European political identity. The other is intergovernmentalism: cooperation among sovereign states while preserving national autonomy. Neither option appears fully adequate. A federation capable of exercising broad fiscal and political authority lacks sufficient democratic support. Pure intergovernmentalism often struggles to provide the European public goods upon which Europe’s prosperity, security, and geopolitical relevance increasingly depend (Bakker et al. 2024, Buti and Messori 2024, Draghi 2024).

Recent proposals for common investments in defence, energy infrastructure, innovation, and strategic autonomy highlight the same problem (Buti et al. 2023, Beetsma et al. 2024, Janse et al. 2025). If sovereign democracies are asked to share risks, financing responsibilities, and strategic commitments, through which democratic institutions can such obligations be authorised and monitored?

This column argues that answering this question requires a new constitutional principle: reciprocal sovereignty.

Reciprocal sovereignty

The modern concept of sovereignty emerged as a principle of independence. Political communities were sovereign because they exercised ultimate authority within their own jurisdiction and remained free from external domination. This conception remains central to democratic self-government.

Yet European integration has transformed the conditions under which sovereignty is exercised. Decisions taken in one democracy increasingly affect citizens and governments in others. Financial instability, energy vulnerabilities, technological dependencies, and security threats rarely respect national borders. The central constitutional question is therefore no longer simply how independence can be preserved, but how interdependence can be governed democratically.

Reciprocal sovereignty begins with this observation. We define it as follows:

Reciprocal sovereignty is the principle that democratic peoples remain sovereign not because they act independently of one another, but because they possess the democratic authority to enter and sustain relations of mutual responsibility.

Reciprocal sovereignty can be understood as a further development of European supranational constitutionalism. In its Maastricht Judgement, the German Federal Constitutional Court described the EU as a Staatenverbund, emphasising that democratic legitimacy derives from the member states and their citizens. Reciprocal sovereignty builds on this insight but introduces an additional dimension. The legitimacy of shared European action depends not only on dual authorisation but also on reciprocal responsibility among democracies.

One way to understand the constitutional development of Europe is through three stages. Classical theories of sovereignty emphasised independence. Post-sovereign and pluralist approaches emphasised the sharing and diffusion of authority (MacCormick 1999, Weiler 1999). Reciprocal sovereignty proposes a third step: the institutionalisation of shared responsibility among sovereign democracies.

This distinguishes reciprocal sovereignty from both federalism and constitutional pluralism. Federalism seeks to align authority and legitimacy through a common sovereign. Constitutional pluralism focuses on the coexistence of multiple sources of authority. Reciprocal sovereignty addresses a different question: how sovereign democracies can become mutually responsible while remaining sovereign.

Its central claim is straightforward. Whenever sovereign decisions generate significant cross-border risks, obligations, or liabilities, democratic legitimacy requires institutions through which the democracies exposed to such consequences can participate in authorising the commitments that create them. Reciprocal authorisation is therefore justified only where sovereign decisions create substantial and foreseeable liabilities for other democracies. Such participation should be understood as a constitutional right available to affected democracies rather than as a mandatory obligation to intervene in the affairs of others. Reciprocity concerns the availability of democratic authorisation rights when substantial cross-border liabilities arise, not a duty of symmetric intervention.

Sovereignty is therefore not abandoned but reinterpreted. Rather than defining sovereignty primarily as freedom from others, reciprocal sovereignty defines it as the democratic capacity to govern interdependence.

The principle can be summarised in a simple proposition:

No European responsibility without reciprocal sovereignty.

Europe can provide common goods only if sovereign democracies possess institutions through which shared responsibilities can be jointly authorised, financed, and monitored.

The democratic triple knot

The ‘democratic triple knot’ represents one institutional embodiment of reciprocal sovereignty. It originated in proposals developed during the Euro Crisis to reconcile fiscal interdependence with democratic legitimacy (Gersbach 2011).

The underlying problem was simple. Fiscal decisions remained national, while their consequences increasingly became European. Countries exposed to the risks generated by another country’s fiscal decisions often lacked any meaningful role in authorising those decisions.

The broader constitutional significance extends far beyond fiscal policy. Whenever decisions in one democracy create substantial risks, liabilities, or obligations for others, democratic legitimacy requires institutions through which the affected democracies can participate in authorising such commitments.

The triple knot consists of three mutually reinforcing elements.

• Joint financing. Countries participating in common European projects share financing responsibilities. Common goods require common commitments. Joint financing transforms cooperation from aspiration into obligation and constitutionalises solidarity.
• Reciprocal authorisation. Countries exposed to common risks participate in decisions that create those risks. No risk-sharing without co-decision. Democratic authorisation therefore extends beyond purely national boundaries while remaining anchored in elected institutions.
• Mutual accountability. Countries benefiting from common commitments accept common monitoring, evaluation, and transparency requirements. Accountability emerges horizontally among democracies rather than hierarchically through a superior authority.

Together, these three elements link responsibility, authorisation, and accountability. The triple knot therefore does more than improve governance. It constitutionalises reciprocity by ensuring that common commitments remain democratically sustainable.

More broadly, recent work on democratic innovation argues that democratic systems must continuously adapt to new collective challenges (Gersbach 2009, 2024, Britz and Gersbach 2026, Landemore 2020). Reciprocal sovereignty provides the constitutional principle; the triple knot provides one mechanism through which that principle can operate. It can thus be understood as a constitutional technology for governing democratic interdependence.

Reciprocal parliamentary approval: An illustration

One possible institutional embodiment of reciprocal sovereignty is reciprocal parliamentary approval. Fiscal policy provides a useful illustration. In this domain, reciprocal parliamentary approval would require the consent of parliaments in selected partner countries whenever a national budget or debt level exceeds agreed thresholds and thereby creates significant potential liabilities for others.

Consider the example of France wishing to run large deficits while Germany strongly objects. Under reciprocal sovereignty, a possible practical implementation of reciprocal parliamentary approval could be as follows: if agreed deficit or debt thresholds are exceeded, the French budget could require approval by a predefined group of partner parliaments selected according to rules agreed ex ante, in particular including Germany. France would then have three options: remain below the threshold, persuade the partner parliaments that exceptional circumstances justify the deviation, or revise the budget if approval is denied. Sovereignty is not abolished, but the exercise of sovereignty becomes conditional when decisions generate significant cross-border risks.

This logic does not depend on symmetric interests. If France does not care about Germany’s fiscal decisions, the mechanism still operates; but France does not need to do anything, as reciprocal parliamentary approval is only a right, not a duty. Member states accept ex ante that decisions creating substantial cross-border liabilities require reciprocal democratic authorisation.

The same reasoning applies to areas involving common-good problems and asymmetric situations more generally. If country A takes a decision that significantly affects country B, while decisions taken by B have little effect on A, reciprocal sovereignty gives B a procedural voice in A’s decision. Authorisation rights follow the direction of responsibility and exposure rather than the symmetry of influence.

This also clarifies how reciprocal sovereignty differs from existing EU fiscal rules. Fiscal rules are primarily technocratic instruments based on numerical limits, monitoring, and sanctions, whose enforcement has often proven politically difficult. Reciprocal sovereignty addresses a different constitutional question: who should have the right to authorise decisions that may impose risks on others? The focus shifts from rule enforcement to democratic co-decision. 

We have illustrated reciprocal parliamentary approval for fiscal policy. More generally, the same constitutional logic could be adapted to other domains in which national decisions generate substantial risks, liabilities, or obligations for partner democracies when common goods are provided. Reciprocal parliamentary approval would ensure that risk-sharing or burden-sharing and democratic authorisation remain institutionally connected. The principle can be summarised as follows: no shared liability without shared authorisation. 

Conclusion

Europe’s future depends increasingly on its capacity to provide common goods. Yet common goods require common responsibilities, and common responsibilities require democratic legitimacy.

Reciprocal sovereignty offers one constitutional framework for addressing this challenge. It suggests that sovereign democracies remain sovereign not despite interdependence, but through their capacity to govern it collectively. The democratic triple knot provides one institutional mechanism through which this principle can be realised.

In Vivien Schmidt’s terminology, Europe must combine input, output, and throughput legitimacy (Schmidt 2013). Reciprocal sovereignty can be understood as an attempt to strengthen the throughput dimension of European democracy by creating procedures through which sovereign democracies jointly authorise, finance, and monitor common commitments.

The central question for Europe is therefore not whether sovereignty should be transferred or preserved. It is whether sovereignty can be reimagined. Reciprocal sovereignty offers one answer. If successful, Europe may become the first political order founded not on sovereign independence alone, but on reciprocal responsibility among sovereign democracies. Its guiding propositions can be stated simply:

No shared liability without shared authorisation. 

No European responsibility without reciprocal sovereignty.

Editors’ note: A longer version of this column, titled “Reciprocal Sovereignty: A Third Constitutional Tradition for Europe. Resilience through Shared Responsibility among Sovereign Democracies” (Gersbach 2026), is available upon request.

References

Bakker, A, R Beetsma and M Buti (2024), “Investing in European public goods while maintaining fiscal discipline at home”, Intereconomics 59(2): 98–103.

Beetsma, R, M Buti and F Nicoli (2024), “Investing in defence as a European public good”, VoxEU.org, 16 September. 

Britz, V and H Gersbach (2026), “Open rule legislative bargaining”, Review of Economic Studies, forthcoming.

Buti, M, A Coloccia and M Messori (2023), “European Public Goods”, VoxEU.org, 9 June.

Buti, M and M Messori (2024), “Sharing Sovereignty and European Public Goods: A Conceptual Framework”, IEP@BU Policy Brief.

Draghi, M (2024), The Future of European Competitiveness, European Commission.

Gersbach, H (2009), “Democratic mechanisms”, Journal of the European Economic Association 7(6): 1436–1469.

Gersbach, H (2011), “‘Triple-Knot’ fiscal safety for the Eurozone”, VoxEU.org, 8 September. 

Gersbach, H (2024), “Forms of new democracy”, Social Choice and Welfare 62: 799–837.

Gersbach, H (2026), “Reciprocal Sovereignty: A Third Constitutional Tradition for Europe. Resilience through Shared Responsibility among Sovereign Democracies”.

Janse, K A, R Beetsma, M Buti, K Regling and N Thygesen (2025), “Gaining efficiencies by financing European public goods together”, VoxEU.org, 10 February. 

Landemore, H (2020), Open Democracy: Reinventing Popular Rule for the Twenty-First Century, Princeton University Press.

MacCormick, N (1999), Questioning Sovereignty: Law, State, and Nation in the European Commonwealth, Oxford University Press.

Schmidt, V A (2013), “Democracy and legitimacy in the European Union revisited: Input, output and ‘throughput’”, Political Studies 61(1): 2–22.

Weiler, J H H (1999), The Constitution of Europe, Cambridge University Press.