Integrating diversity in the European Union (InDivEU) : fundamental rights as constraints to and triggers for differentiated integration : policy brief.
Date: 2022-07-18
Institutions: European University Institute
Subjects: EU Charter of Fundamental Rights, European Union, European integration, democracy, enhanced cooperation, fundamental rights

Integrating Diversity in
the European Union (InDivEU)

Fundamental Rights as Constraints 
to and Triggers for Differentiated 
Integration1

Summary

When looking for possible constraints on Differentiated Integration, 
the fundamental values of the European Union (EU) seem an obvious 
starting point. Both the Charter of Fundamental Rights and the values 
articulated in Art. 2 TEU are cross-cutting across EU states. However, 
while fundamental values have acted as centralising devices in other 
federal  settings,  in  an  EU  context  marked  by  extensive  value  dis-
agreement, they may also act as pathways for differentiation. Insofar 
as national constitutional orders disagree on the scope of EU rights, 
attempts to ground EU law in fundamental values trigger inevitable 
interpretive conﬂicts across states. This paper will use the examples 
of  asylum  and  the  European  Arrest  Warrant  to  demonstrate  this 
argument: while EU law may use fundamental values as a reason to 
harmonise EU law across states, such values may also be invoked 
to question the principle of mutual trust underlying the EU legal order, 
thereby causing rather than limiting differentiation.

When looking for possible constraints on Differentiated Integration, 
the fundamental values of the European Union (EU) seem an obvious 

1  This short policy brief is based on the findings of a larger article. E. Bertolini and M. Daw-
son,  ‘Fundamental  Rights  as  Constraints  to  and  Triggers  for  Differentiated  Integration’ 
(2021, forthcoming) Swiss Political Science Review.

Authors

Julien Bois, Postdoctoral researcher at the University of Liege 
Mark Dawson, Hertie School of Governance, Professor for European 
Law and Governance

The project has received funding from the European Union’s Horizon 2020 
research and innovation programme under grant agreement No 822304

Issue 2022/25
April 2022

http://indiveu.eui.eu

POLICY BRIEFstarting point. Both the Charter of Fundamental 
Rights  and  the  values  articulated  in Art.  2 TEU 
are  cross-cutting  across  EU  states.  However, 
while  fundamental  values  have  acted  as  cen-
tralising  devices  in  other  federal  settings,  in  an 
EU context marked by extensive value disagree-
ment, they may also act as pathways for differen-
tiation.  Insofar  as  national  constitutional  orders 
disagree on the scope of EU rights, attempts to 
ground EU law in fundamental values trigger in-
evitable interpretive conﬂicts across states. This 
policy  brief  uses  the  examples  of  asylum  and 
the  European  Arrest  Warrant  to  demonstrate 
this  argument:  while  EU  law  may  use  funda-
mental values as a reason to harmonise EU law 
across states, such values may also be invoked 
to  question  the  principle  of  mutual  trust  under-
lying the EU legal order, thereby causing rather 
than  limiting  differentiation.  It  will  formulate  a 
list of recommendations that could address the 
potential  issues  raised  by  differentiation  in  the 
application of fundamental rights.

Differentiated integration versus 
differentiation

Fundamental rights (FR) and the rule of law con-
stitute the fundamental values of the EU. Unlike 
other  policy  areas  such  as  monetary  or  border 
policy,  fundamental  values  are  not  subject  to 
differentiated integration, i.e. to the formal appli-
cation  of  different  rules  across  member  states. 
As  these  values  are  enshrined  in  the  Charter 
of Fundamental rights (CFR) and are protected 
by  the  EU’s  highest  court,  namely  the  Court  of 
Justice of the European Union (CJEU), EU fun-
damental values are centralised. 

Uniform integration does not, however, eliminate 
the possibilities for differentiation across member 
states.  Differentiation  refers  to  the  existence  of 
diverging  practices  across  member  states  in 
how they apply EU values in their domestic legal 
orders.  While  central  principles  remain  across 
Member States, the thresholds for fundamental 
rights protection differ across jurisdictions.

Differentiation  of  rights  protection  thus  entails 
the following:

equivalent  practice  as  acceptable  (either 
because  they  interpret  this  legal  standard 
differently  or  because  they  disagree  about 
the underlying facts). Differentiation can thus 
arise from disagreement on how FR should 
be interpreted.

•  Differentiation of standards also has effects 
on  other  EU  policies,  such  as  common 
asylum  policy  or  cooperation  in  criminal 
matters.  Differentiation  can  thus  arise  from 
derogation,  where  national  orders  defy  EU 
policies  e.g.  in  the  asylum  or  criminal  field, 
because  following  them  would  infringe  the 
core  of  a  FR  protected  under  the  national 
constitution.

Differentiated 
integration
Different formal 
application 
of the rules 
(Treaties, 
secondary 
legislation)

Differentiation

Different 
practices across 
jurisdictions 
despite the 
existence of 
common rules

Definition

Application 
to EU FR

NO

YES

Different 
thresholds leading 
to disagreement 
or to derogation

Differentiation in practice: limits to 
mutual trust in the EU

Different thresholds of FR protection do not pose 
a problem when member states act in isolation. 
EU law recognizes the administrative autonomy 
of the member states, and the ability of national 
orders  to  apply  national  constitutional  rights 
where outside of EU law’s scope.2 However, dif-
ferentiation challenges the uniform application of 
EU law when national legal orders must interact. 
A  common  set  of  FR  supposes  the  existence 
of  mutual  trust  between  legal  orders,  i.e.  that 
national authorities recognize practices of other 
member  states  as  equivalent  in  terms  of  rights 
protection.

•  Within  the  FR  field  itself,  administrations 
and courts apply different thresholds. This 
means that while a Court in one member state 
may consider a national practice an example 
of  “inhuman  and  degrading  treatment”,  a 
Court  in  another  state  may  consider  an 

However,  divergent  practices  across  member 
states trigger differentiation and thus bring limits 
to mutual trust:

•  The  existence  of  a  potential  rebuttal  of  the 
principle of mutual trust: the CJEU still favors 

2 

 Art. 51(1) EU Charter of Fundamental Rights

2  

  Robert Schuman Centre | April 2022

mutual  trust  and  the  uniform  application  of 
EU law, even where FR issues are affected. 
But it has opened the possibility for diverging 
national practices, albeit only in the case of 
inhumane  and  degrading  treatment3.  This 
possibility  remains  narrowly  circumscribed 
in  practice  since  the  CJEU  accepted  dif-
ferentiation  only  after  the  European  Court 
of  Human  rights  condemned  EU  member 
states for favoring the application of EU law 
over  the  protection  of  FR  (thus  breaching 
their obligations under the ECHR)4.

•  FR  protection  is  a  process  in  ﬂux:  the  in-
tervention  of  the  legislator  and  the  CJEU 
create  a  centripetal  effect  that  centralizes 
and harmonizes the protection of rights. But 
the  subsequent  interventions  of  national 
administrations  and 
judiciaries,  coupled 
with  ECHR  case  law,  create  a  centrifugal 
effect that increases the diversity of practice 
across the EU. The latter is especially clear 
in  the  field  of  common  asylum  policy,  since 
several national courts have disregarded the 
strict  conditions  of  the  CJEU,  refusing  the 
transfer of asylum seekers to other Member 
States where inhuman conditions were likely 
to result. Some national courts prefer to rely 
on interpretations of the ECHR when issuing 
decisions with a FR component.

Causes for differentiation in FR 
across the EU

If there is a high degree of differentiation in FR, 
what  causes  this  differentiation?  Three  major 
causes can be identified:

•  Rule 

indeterminacy: 

fundamental  values 
remain  abstract  principles  that  must  be 
adjusted to specific situations. While mutual 
trust presupposes an equivalence of FR pro-
tection across member states, the appraisal 
of standards is likely to diverge between ad-
ministrations  and  courts  on  the  one  hand, 
and  between  different  member  states  on 
the other. Even communications and frame-
works  developed  by  the  legislator  and  the 
Commission may not fully remove legal dis-
agreements.

•  Factual  indeterminacy:  even  if  there  is  a 
certain agreement about the interpretation of 

common rules, actors must cope with specific 
cases  with  their  subjective  assessments 
and cannot process data and evaluations of 
other  member  states  to  the  greatest  extent 
theoretically  available.  For  example,  the 
Higher Regional Court of Bremen assumed 
that the Latvian prison system suffered from 
systemic deficiencies even if Latvian author-
ities claimed the opposite5.

•  Cultural  indeterminacy:  Legal  actors  might 
disagree  on  the  prioritization  of  different 
norms, and this is likely to reﬂect the weight 
given  to  particular  values  within  their  re-
spective  legal  systems.  Even  if  the  core  or 
‘essence’  of  fundamental  rights  is  common 
to all member states, the moral character as-
sociated to rights protection will likely trigger 
disagreements  across  states.  Even  if  cen-
tripetal  forces  led  by  the  CJEU  lead  to  en-
compassing guidelines of interpretation, the 
specificity  of  cases  (such  as  the  perceived 
deservingness  of  litigants)  and  the  different 
backgrounds  of  actors  involved  will  play  a 
centrifugal role.

Causes for differentiation in FR protection

Rule 
indeterminacy
Different 
understanding 
of moral values 
associated to 
FR protection

Factual 
indeterminacy
Different/
bounded 
knowledge of 
other national 
legal systems

Cultural 
indeterminacy
Divergence 
about the 
hierarchization of 
moral standards

Conclusion and recommendations: 
Unity in diversity

Thus,  while  FR  and  fundamental  values  are 
formally not subject to differentiated integration, 
their interpretation may lead to differentiation of 
practices  across  member  states.  This  finding 
may not necessarily raise a need for immediate 
correction. While mutual trust is an overarching 
value of the EU, the administrative autonomy of 
member states is also a constitutional principle 
of the Union. The latter therefore recognizes the 
legitimate existence of different practices across 
member  states,  as  long  as  the  equivalence  of 
rights protection remains unaffected.

3 

4 
5 

 C-411/10, NS and others, 2011. See Xanthopoulou, E. (2018). Mutual trust and rights in EU criminal and asylum law: three phases 
of evolution and the uncharted territory beyond blind trust. Common Market Law Review 55(2):489–509
 ECHR, MSS v. Belgium and Greece, 2011 and Varga and Others v. Hungary, 2015
 Higher Regional Court Bremen (2016). Order of 3 August 2016 - 1 Ausl A 14/15

3  

  Fundamental Rights as Constraints to and Triggers for Differentiated Integration

damental  rights  common  to  all  EU  member 
states  remains  unaffected  by  diverging 
practices.  They  should  however  respect 
decisions that do not disregard that core yet 
display  deference  to  national  specificities, 
particularly when in refusing to apply EU law, 
national Courts uphold a higher standard of 
fundamental rights protection. The autonomy 
of Members states to protect core elements 
of the national constitutional order in respect 
to  FR  should  be  strengthened  rather  than 
weakened through the operation of Europe’s 
area of freedom, security and justice.

EU  actors  may  nonetheless  play  an  important 
role  in  limiting  the  effects  of  differentiation  and 
enhancing  mutual  trust  among  national  legal 
orders. The recommendations below thus stress 
the  possible  cooperative  paths  that  could  be 
(further)  developed,  addressing  each  of  the 
causes of differentiation mentioned above.

1.  In addressing rule indeterminacy, the CJEU 
shall keep its centripetal role as a harmoniz-
ing  FR  protector  in  the  EU  but  should  use 
the mechanism of the preliminary reference 
procedure  to  foster  cooperation.  In  prelimi-
nary  rulings,  it  may  indicate  to  the  referring 
judge supplementary sources of information 
about the protection of FR in other member 
states  and  should  seek  to  provide  more 
detailed guidance on how applicable EU law 
should be interpreted. Since national judges 
may not be aware of the specificities of other 
national  legal  orders  in  the  EU,  the  Court 
shall use its considerable resources to guide 
national  courts  –  which  will  issue  the  final 
decision – towards informed and consistent 
decisions. 

2.  In  addressing  factual  indeterminacy,  the 
European  Commission,  working  with  the 
Fundamental  Rights  Agency,  shall  monitor 
closely  and  regularly  the  differentiated  ap-
plication  of  FR  protection  across  member 
states. It shall pinpoint the areas that trigger 
(e.g.  European 
increased  differentiation 
Arrest  Warrant  and  the  transfer  of  asylum 
seekers)  and  issue  communications  and 
research  notes  that  contain  updated  infor-
mation  of  the  current  state  of  play  across 
member  states.  Updates  occurring  every  5 
years would reduce the likelihood of differen-
tiation. Centralised information on the factual 
operation of systems based on mutual trust 
(such  as  asylum  conditions  in  EU  member 
states) could considerably help national and 
European  Courts  in  making  consistent  and 
evidence-based  decisions  on  how  mutual 
trust principles should be applied.

3.  In  addressing  cultural  indeterminacy,  EU 
institutions  can  utilize  the  notion  of  an 
‘essence’  of  fundamental  rights  as  estab-
lished  in  the  Charter  to  orient  a  meaningful 
division  of  labour  between  the  national  and 
EU  levels  regarding  FR  protection.6  EU  in-
stitutions  must  ensure  that  the  core  of  fun-

6 

 M. Dawson, O. Lynskey & E. Muir, ‘What is the Added Value of the Concept of the “Essence” of EU Fundamental Rights?’ (2019) Ger-
man Law Journal, 20(6).

4  

  Robert Schuman Centre | April 2022

Integrating Diversity in the European Union (InDivEU) is a Horizon 2020 funded research 
project aimed at contributing concretely to the current debate on the ‘Future of Europe’ by 
assessing,  developing  and  testing  a  range  of  models  and  scenarios  for  different  levels  of 
integration among EU member states. 

InDivEU is coordinated by the Robert Schuman Centre at the European University Institute, 
where  it  is  hosted  by  the  European  Governance  and  Politics  Programme.  The  project 
comprises a consortium of 14 partner institutions and runs from January 2019 to December 
2021.  The  scientific  coordinators  are  Brigid  Laffan  (Robert  Schuman  Centre)  and  Frank 
Schimmelfennig (ETH Zürich). 

© European University Institute, 2022
Editorial matter and selection © Julien Bois, Mark Dawson, 2022

This work is licensed under the Creative Commons Attribution 4.0 (CC-BY 4.0) Internation-
al license which governs the terms of access and reuse for this work. If cited or quoted, 
reference should be made to the full name of the author(s), editor(s), the title, the series and 
number, the year and the publisher.

Views expressed in this publication reﬂect the opinion of individual authors and not those of 
the European University Institute.

Published by
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doi:10.2870/775089
ISBN:978-92-9466-201-9
ISSN:2467-4540
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The project has received funding from the European Union’s Horizon 2020 research 
and innovation programme under grant agreement No 822304

5  

  RSC | Policy Brief | April 2022