The 9th May is celebrated by the European Union like a national day, as it would have officially been if the European Constitution Treaty were successful. The date commemorates the speech held on the same day in 1950 by Robert Schuman, now often designated as one of the founding fathers of the EU. Regarded as the landmark of the European journey’s beginning, the Schuman Declaration names a foundational concept of the European project: solidarity. Only then concretised with the ratification of the Treaty of Paris in 1952 which founded what would become the European Union, the idea of creating a pan-European solidarity is not new. Victor Hugo, one century earlier in 1849, saw in the creation of a European fraternité the inevitable destiny of European nations, thereby uniting the peoples of the old continent under the auspices of a supranational authority where wars are substituted with legal battles while preserving the nations’ “glorious individuality”. The similarities with the modern EU here are striking. Early on, solidarity was considered as the end of the European project, which led the Advocate General Bot to call it as “both the raison d’être and the objective of the European project”.
What customs strictly divided
Emile Durkheim, one of the principal architects of modern social science, distinguishes between two forms of solidarity: organic and mechanical. The former characterises heterogeneous societies only bound by the interdependence of its members, where each member’s contribution is essential to the society’s development. This type of solidarity typically arises in a situation of a division of labour where each is specialised in producing a peculiar advantage, thus following the economic logic behind the theories of comparative advantage developed by Adam Smith and David Ricardo. But organic solidarity relies on self-interest and on what members can bring to one another. For this reason, organic is a weaker form of solidarity than mechanical. The latter depends on the sameness of the society’s members, characterised by a homogeneous culture, life-style and shared values. These give birth to a collective consciousness, further advanced with the development of social bonds, where members assist one another not on selfish considerations but on sameness. It follows that this type of solidarity is proportionately stronger as the society is homogeneous. Therefore, what creates a link between different members of a society (trade or common features) determines the nature and level of solidarity binding them. The European integration process observes a shift from a weaker organic solidarity to a stronger mechanical solidarity.
Schuman viewed the pooling of resources as a means to create a de facto solidarity. This led to the monumental task of establishing a single market. First limited to coal and steel and to later include the free movement of all goods marketed in the EU, the single market expanded to the free movement of workers and now to all the nationals of the Member States regardless of their professional status. The later expansion was made possible by the Maastricht Treaty in 1992 with the introduction of the notion of EU citizenship which is destined to become the “fundamental status of nationals of the Member States”, thus ignoring internal borders. The rights attached to EU citizenship, such as the right to freely move and reside in another Member State are designed to strengthen a sense of belonging to Europe and to promote social cohesion among EU citizens, one of the EU’s fundamental objectives. The deepening of solidarity between the peoples of Europe is indeed one of the goals pursued by the Union, as recalled in the preamble of the Treaty on European Union (TEU).
To this end, EU citizens from one Member State enjoy equal treatment with that of the nationals of another Member State. Consequently, EU citizens can claim social assistance like nationals of the host Member State and Member States owe a certain degree of financial solidarity to them. This cross-border solidarity directed towards individuals is crucial to encourage intra-EU mobility, interactions and exchanges between EU citizens. This results in a homogenisation of European society as a step towards a mechanical solidarity binding Member States and their peoples.
Evidently, a European mechanical solidarity will not be spontaneous and can only arise in the long term. Intra-EU mobility currently remains limited. Only 3.3% of EU citizens of working age (20-64) resided in another Member State in 2020. Besides, mobility is notably limited by the condition that EU citizens must be financially self-sustainable and possess a sickness insurance for at least the first five years of residency in order to enjoy equal treatment and subsequently be entitled to social assistance and access to social security schemes. Nevertheless, this does not preclude the EU from institutionalising the path towards mechanical solidarity through the establishment of common values and objectives.
Above twelve stars must a value and an objective dwell
The Charter’s preamble qualifies solidarity as an “indivisible, universal values” on which the EU is founded, which, read in conjunction with Article 2 TEU, confirms scholars’ views that solidarity constitutes an EU value. As such, solidarity constitutes a core element of the EU acquis, thus, acceding States must adhere to it and accept to demonstrate it towards the EU and the other Member States and their peoples as a result of their EU obligations. Hence, the EU often insists that it also is a union of values. Article 7 TEU, the so-called nuclear option, renders values binding and enforceable, whereby the finding of a clear risk of a serious breach of EU values may result in the suspension of EU-derived rights such as the Member State’s voting right in the Council. However, Article 7 TEU is rarely used because of its heavy political meaning and its complex procedure.
Moreover, solidarity is also presented as an objective of the Union. Article 3(3) TEU sets the objective of promoting solidarity between generations and Article 21 TEU provides that the Union’s external action is guided “by the principles which have inspired its own creation, development and enlargement” including inter alia the principle of solidarity. The very notion of solidarity underlies the European project and is consequently one of the principles highlighting the EU’s external relations. The same holds true for the EU’s internal action, by virtue of Article 7 TFEU where the Union must ensure consistency between its policies and activities and take into account all of its objectives. Altogether, all policies and activities of the EU and its Member States when they act within the scope of EU law must pursue the objective of demonstrating and strengthening solidarity.
A general principle’s magic binds again
More than a value and an objective, solidarity “is at the basis of the whole of the Union system”. It characterises all the rights and obligations binding the EU and its Member States. The choice of a common destiny by way of EU membership imposes that, in accordance with the principle of solidarity, Member States may not act on their own conception of national interest. The Court of Justice of the European Union (CJEU) observed that EU law provides advantages to the Member States and their nationals, and in order to respect an equal enjoyment of the rights derived therefrom throughout the Union, the EU institutions and Member States have to obey its rules. A violation of EU obligations thus breaks the equilibrium between advantages and obligations flowing from the Treaties and brings into question the equality of Member States before EU law. Additionally, this creates discriminations at the expense of their nationals, and above all of the nationals of the contravening State which places itself outside the EU rules. Therefore, the Member States respecting their obligations would then have to suffer the consequences and cope with the behaviour of that particular State. That would result in an unfair burden on the non-breaching Member States, which is contrary to the duty of solidarity inherent to EU membership and to the EU legal order. It follows that a deviation from EU rules also represents a threat to the principle of unity on which the Union is based.
The EU’s unity is best portrayed in the single market but is also present in other policy areas, such as in external relations, where Member States must not interfere with the EU’s actions and take all appropriate measures to defend the EU’s interests. The requirements of unity and solidarity attached to the very purpose of the EU underlie the rationale of sincere cooperation, whereby the EU and its Member States shall assist each other and take any appropriate measure to carry out the tasks flowing from the Treaties or resulting from the acts of EU institutions and Member States shall “refrain from any measure which could jeopardise the attainment of the Union’s objectives”. Likewise, solidarity lies at the core of the principle of mutual assistance.
The fact that solidarity underpins the whole Union system and gives rise to major principles of EU law elevates the notion to a general principle of EU law. The general principle of solidarity entails a reciprocal obligation between the EU and its Member States and between the Member States themselves to take into consideration the interests of the other stakeholders, including individuals. That general principle is expressed in many fields of law and differently. European solidarity has been identified to underlie the single market, external relations, fundamental rights, energy law, environmental law, asylum law, the common fisheries policy, the financial mechanisms for countries outside the eurozone, the economic, social and territorial cohesion policies based on Articles 174 to 178 TFEU, and the European budget. This is especially so with the issuance of a common debt and the recovery package Next Generation EU to help Member States recover from the financial hardships caused by the Covid-19 outbreak. Whilst it is not a closed list, solidarity is omnipresent within the Union. All of these expressions of solidarity convey a leitmotif, they define a relationship of reciprocal responsibility or obligation to assist one another to face vulnerabilities.
Because general principles are used by the CJEU as an interpretation grid and can be used to review EU law, solidarity will become decisive in the Court’s future rulings. The recognition of solidarity as a general principle of EU law fosters a legal interpretation based on solidarity and mutual assistance, thus emphasising a change of paradigm in the conceptualisation of Union law and policies.
All EU citizens become brothers
The European project is, therefore, a project of peace and solidarity. First defined by the single market, solidarity is destined to grow among Member States and EU citizens. Whereas there are limits to the development of solidarity, the overarching goal of creating an ever closer union enshrined in Article 1 TEU aims at erasing those limits. Hence, the level of solidarity is closely linked to the level of European integration. A strong level of European solidarity will thus only come about with the development of EU law and the harmonisation of national laws, as means to abolish internal borders and create a collective consciousness of belonging to the same society bound by a common destiny.
Such a feeling of belonging arises through concrete achievements, including the institutionalisation of shared values, the recognition of common interests to be collectively pursued and the development of a law binding them all. All interactions will then be characterised by the very definition of solidarity. Treaties and secondary laws inherently, by the ideal motivating their creation, thrive in this direction. It is therefore “next to impossible to exclude any form of solidarity between Member States as long as the European Union exists”. Solidarity truly is “the lifeblood of the European project”.
Happy Europe Day!
 Treaty establishing a Constitution for Europe  OJ C310/1, art I-8.
 Robert Schuman, ‘Declaration of 9th May 1950’ , accessible at ‘Declaration of 9 May’ (Fondation Robert Schuman) <Declaration of 9 may – Robert Schuman Foundation (robert-schuman.eu)> accessed 5 May 2022.
 Victor Hugo, Ouverture speech of the International Peace Congress , accessible at ‘Discours d’ouverture du Congrès de la Paix, le 21 août 1849’ (Herodote.net) <https://www.herodote.net/Textes/victor-hugo-discours-du-congres-de-la-paix.pdf> accessed 5 May 2022.
 Joined Cases C-643/15 and C-647/15 Slovakia and Hungary v Council of the European Union  ECLI:EU:C:2017:618, Opinion of AG Bot, para 17.
 Emile Durkheim, La Division du travail social (first published 1893, OUP 2012) 143.
 ibid; Steinar Sternø, Solidarity in Europe: The History of an Idea (Cambridge University Press 2005) 33.
 Durkheim (n 5) 143.
 Case C-184/99 Rudy Grzelczyk v Centre public d’aide sociale d’Ottignies-Louvain-la-Neuve  ECLI:EU:C:2001:458, para 31 ; Case C-413/99 Baumbast and R  ECLI:EU:C:2002:493, para 82; Case C-224/98 Marie-Nathalie D’Hoop v Office national de l’emploi  ECLI:EU:C:2002:432, para 28.
 Directive 2004/38/EC of the European Parliament and of the Council of 29 April 2004 on the right of citizens of the Union and their family members to move and reside freely within the territory of the Member States amending Regulation (EEC) No 1612/68 and repealing Directives 64/221/EEC, 68/360/EEC, 72/194/EEC, 73/148/EEC, 75/34/EEC, 75/35/EEC, 90/364/EEC, 90/365/EEC and 93/96/EEC  OJ L158/77 (Citizens’ Rights Directive), recital 17.
 Consolidated Version of the Treaty on the Functioning of the European Union (TFEU)  OJ C 202/47, art 18.
 Case C-184/99 Grzelczyk (n 8) para 44; Case C-209/03 The Queen, on the application of Dany Bidar v London Borough of Ealing and Secretary of State for Education and Skills  ECLI:EU:C:2005:169, para 56.
 ‘EU citizens living in another Member State – statistical overview’ (Eurostat, 12 October 2021) <https://ec.europa.eu/eurostat/statistics-explained/index.php?title=EU_citizens_living_in_another_Member_State_-_statistical_overview#Who_are_the_most_mobile_EU_citizens.3F> accessed 5 May 2022.
 Case C-333/13 Elisabeta Dano and Florin Dano v Jobcenter Leipzig  ECLI:EU:C:2014:2358, paras 60-61; Case C-158/07 Jacqueline Förster v Hoofddirectie van de Informatie Beheer Groep  ECLI:EU:C:2008:630, para 60.
 Charter of Fundamental Rights of the European Union (Charter)  OJ C 326/391; Peter Hilpold, ‘Understanding Solidarity within EU Law: An Analysis of the ‘Islands of Solidarity’ with Particular Regard to Monetary Union’ (2015) Yearbook of European Law 257, 258; Violeta Moreno-Lax, ‘Solidarity’s Reach: Meaning, Dimensions and Implications for EU (External) Asylum Policy’ (2017) 24 Maastricht J Eur & Comp L 740, 747; Irina Domurath, ‘The Three Dimensions of Solidarity in the EU Legal Order: Limits of the Judicial and Legal Approach’ (2012) European Integration 1, 1; E. Dagilyté, ‘Solidarity: a general principle of EU law? Two variations on the solidarity theme’ in A Biondi, E Dagilytė and E Küçük (eds), Solidarity in EU Law: Legal Principle in the Making (Edward Elgar 2018) 62.
 Kim Lane Scheppele, Dimitry Vladimirovich Kochenov and Barbara Grabowska-Moroz, ‘EU Values Are Law, after All: Enforcing EU Values through Systemic Infringement Actions by the European Commission and the Member States of the European Union’ (2020) 39 Yearbook of European Law 4, 35.
 Joined Cases 6 and 11/69 Commission of the European Communities v French Republic  ECLI:EU:C:1969:68, para 16; Case T-883/16 Republic of Poland v European Commission  ECLI:EU:T:2019:567, para 69.
 Case 39/72 Commission v Italy (Premiums for slaughtering cows)  ECLI:EU:C:1973:13, para 24.
 ibid, para 25; Case 128/78 Commission v United Kingdom (Tachographs)  ECLI:EU:C:1979:32, para 12.
 Joined Cases 9 and 12-60 Société commerciale Antoine Vloeberghs SA v High Authority of the European Coal and Steel Community  ECLI:EU:C:1961:18, p. 215.
 Case 22/70 Commission v Council (ERTA)  ECLI:EU:C:1971:32, paras 21-22 and 31.
 Treaty on the Functioning of the European Union (TFEU), art 4(3); Joined Cases 9 and 12-60 Société commerciale Antoine Vloeberghs SA (n 20).
 Pierre Pescatore, ‘Les objectifs de la Communauté européenne comme principe d’interprétation dans la jurisprudence de la Cour de justice’ in Miscellanea W. J. Ganshof van der Meersch, vol 2 (E. Bruylant 1972); Epaminondas A. Marias, ‘Solidarity as an objective of the European Union and the European Community’ (1994) Legal Issues of Economic Integration 85, 99; Joined Cases 9 and 12-60 Société commerciale Antoine Vloeberghs SA (n 20).
 Case T-883/16 Poland v Commission (n 16), para 69; Under appeal, the Court of Justice confirmed the finding that solidarity is indeed a general principle of EU law : Case C-848/19 P Germany v Poland  ECLI:EU:C:2021:598, para 71.
 Case T-883/16 Poland v Commission (n 16), paras 70 and 72.
 Charter (n 14), Title IV ‘Solidarity’.
 Case C-848/19 P Germany v Poland (n 24).
 Domurath (n 14) 6-7; Marta Torre-Schaub, ‘La solidarité environnementale en droit communautaire’ in C Boutayeb (ed), La solidarité dans l’Union européenne : Eléments constitutionnels et matériels (Dalloz 2011).
 Joined Cases C-411/10 and C-493/10 N. S. v Secretary of State for the Home Department and M. E. and Others v Refugee Applications Commissioner and Minister for Justice, Equality and Law Reform  ECLI:EU:C:2011:865, para 93.
 Case C-63/83 Regina v Kent Kirk  ECLI:EU:C:1984:255; Marias (n 23) 101.
 Case C-848/19 P Federal Republic of Germany v Republic of Poland, European Commission  ECLI:EU:C:2021:218, Opinion of AG Campos Sánchez-Bordona, para 59.
 Case C-156/21 Hungary v European Parliament and Council of the European Union  ECLI:EU:C:2022:97, para 129.
 Domurath (n 14) 2.
 Hilpold (n 14) 280.
 Joined Cases C-715/17, C-718/17, C-719/17 Commission v Poland, (Temporary mechanism for the relocation of applicants for international protection)  ECLI:EU:C:2019:917, Opinion of AG Sharpston, para 253.