1. The link between international law's humanization and constitutionalization, and the article's scope

The theory of the humanization of international law might be seen as contiguous or even complementary to the theory – or theories – on the constitutionalization of international law.Footnote ¹ As is well known, the humanization theory argues that human rights have had, and continue to have, major impacts on numerous areas of international law, which, owing to that influence, is now perceived as an increasingly humanized legal system.Footnote ² While there is no single conceptual denotation of constitutionalization, it could be summarized as an intellectual ‘project, which argues that the international legal order beyond the state exists and has a backbone, a foundational set of norms’.Footnote ³ Human rights could be seen as part of that foundational set of norms, and a common locus that bridges the two named, separate but interlinked narratives of international law and the international legal order. ‘Other than the object of the humanization of international law, human rights are one of the “ingredients” of [its] constitutionalization.’Footnote ⁴

This article focuses on that common ingredient – i.e., human rights – of the two named theories and observes that the transplantation of human rights from national constitutions to international law has generated major systemic changes in the latter's order that could be described by proponents of the constitutionalization theory as constitutional in nature. The core assumption we make is that the internationalization of national constitutions,Footnote ⁵ and especially of their human rights protection provisions, has led to the “constitutionalization” of international law.Footnote ⁶ This movement is reflected in the paper's title that asks whether the international legal system is moving towards the direction of acquiring a humanized “constitution”. Two preliminary explanations are due at this point.

First, there is a reason why the terms “constitution” and “constitutionalization” are between quotation marks in the previous paragraph as well as in the paper's title. In essence, we are somewhat critically “agnostic” about the constitutionalization narrative, and its power as a metaphor to explain international law and its structures. The reasons for our scepticism are briefly discussed in Section 2 of the article, but for now we would like to preface our position to the reader by saying that international law, like all legal orders, has always contained certain systemic characteristics that underpin its order,Footnote ⁷ and which are exclusive to it and stem from the nature of the society that developed it for its own needs and use. International law is a state-centric, decentralized, quasi-anarchic legal system. Such is the être of its constitutive society. Its core principles, sovereignty and equality, reflect the basic feature of its main “actors”, i.e., states exercising the ultimate power and authority on a certain territory and over certain people, and the fact that sovereign states live in a society that recognizes no superior authority than their very own sovereignty, leading thereby to the horizontality of the relationship between equals. Sovereignty is inextricably associated with power, and the decentralized nature of international law reflects the decentralization of power. The absence of centralization produces inter-subjective relations (ergo, the deficiency – in principle – of objectiveness),Footnote ⁸ based on reciprocity and self-help. These are the key features of the Westphalian model,Footnote ⁹ which, of course, modern international law (also because of human rights, as this paper will argue) has gradually mitigated and tempered. However, these very characteristics, as well as others such as the absence of the Hartial rule of recognition,Footnote ¹⁰ which for reasons of brevity cannot be mentioned here, remain central to international law, forming the basis that founds its system. Thus, in a sense they are “constitutional”.

If by constitutionalization we mean the existence of certain structural features of the legal order, then international law has always had a “constitution”. This constitution is informal (which is yet another reason explaining why the term is only used metaphorically) in its nature and delineates the structure (but also the confines) of its legal order. Yet, the term constitutionalization refers to something emerging;Footnote ¹¹ rather than pointing to the aforementioned well known, and very old “constitutional” attributes of international law, it aspires to trace the signs of a dynamic transformative process marked by the emergence of a renewed constitutional “edifice”. However, to effectively debate the forces and nature of any transformation observed in the international legal system, we ought not to lose sight or underrate the foundational “constitutional” features of the international system. For the metaphor to be valid, in lieu of “constitutionalization”, the word should be that of a “constitutional reform” –and such a reform cannot be but equally informal, as the “constitution” of international law is, and has always been. Human rights are part of that “reform” and associated with changes affecting the general systemic features of international law.

Second, thus far, scholarship (admittedly, particularly European and North American scholarship) has largely referred to constitutionalization in the context of explaining why and how international law is developing what authors see as elements of a constitution. Next to that basic strand, one could add scholarly work studying how international law (and especially human rights) affects national constitutions.Footnote ¹² We would like to add to that literature by framing some of its core contributions within debates on the constitutionalization of international law, but also by adding a third strand of debate concerning the impact national constitutions and their human rights provisions have or have had on the systemic premises and basic features of international law. Therefore, our intervention is unavoidably also doctrinal in nature (especially Section 4 of the study), even if we are informed by theoretical insights.

Thus, in this article, we take a step back in the debate(s) on the constitutionalization of international law by identifying the origins of that transformative (and circular,Footnote ¹³ in essence) process. Our core contention is that the internationalization of human rights law – to the extent that it is reflected in positive international law and is not simply a moral aspirationFootnote ¹⁴– has led to the development of certain significant features that were initially either anaemic, or even entirely absent from “classic” international law. These new features that the order of international law has acquired through the internationalization of human rights – and this is what makes them in a sense constitutional – amount now to structural elements of the international system that apply well beyond human rights as a specialized field of international law. Had they been exclusive to human rights, they would only be characteristics of self-contained-ness, and not essential, organizational, underlying constituents of the system of international law as such.

This is besides what makes the theory of the humanization of international law contiguous to that of constitutionalization. The shift in the protection of human rights from the national to the international level made it necessary for certain new systemic features to be developed in the order of international law. That is, for international law to effectively accommodate human rights protection, across the many different strands and implementing organs of this diverse body of international law,Footnote ¹⁵ it had to change. These changes can be seen as a sign of a type of humanization that – unlike other special questionsFootnote ¹⁶ or subject-matters on which human rights were understood as having an impact – affects the systemic premises of the international order. For those who endorse the constitutionalization metaphor, these are “constitutional” features. This is what justifies the paper's main argument, namely, that the internationalization of national constitutions has led to the “constitutionalization” of international law. Naturally, human rights law is not necessarily the only feature of domestic constitutionalism that has had an impact on international law. One could argue, for instance, that separation of powers issues in domestic constitutions have had an influence on international law, as part of the literature on the constitutionalization of international law suggests. Another example is the endless debate about the democratization of international law.Footnote ¹⁷ But, for the purposes of this article, we focus on the influence of human rights, even if it is not a feature of all constitutions in the world.Footnote ¹⁸

As mentioned above, Section 2 of this article critically evaluates the main tenet of the theory of constitutionalization and its principal assertion that international law develops a constitution. Section 3 discusses the links between human rights and the constitutionalization of international law. Although human rights are not exclusive to that particular account of the international legal order (i.e., the constitutionalization), they are central to it, and they fit easily within the constitutional narrative, and in many ways advance it. Section 4 discusses the internationalization of human rights and how that regime of international law has contributed to the change of the international order, in that its system had to develop certain systemic tools to allow human rights to develop their full effet utile, and facilitate effectiveness through collective enforcement. In that respect, the article identifies three main changes: i.e., collective enforcement at the decentralized level for the protection of common interests and/or values; ii. sui generis normative hierarchy beyond jus cogens; and iii. responsibility of states to protect (linked with the principle of due diligence and the so-called positive effect that human rights develop). It goes without saying that the “privileged” place human rights occupy as a branch of international law within its system and the idea of their specialty (which, besides, is linked to all three changes) cannot be dissociated from the values found in their very existential core or, to use a more technical term, the material sources that nourish them. Section 5 concludes our analysis.

2. Critiquing the constitutionalization of international law

Is international law developing a constitution? This is the principal question at the heart of the scholarly debate on the constitutionalization of international law. There are two main critical comments that can be made in that respect.

Before that, a competence “disclaimer” is due. Constitutionalization is more of a constitutional law question, and less of an international law one. Therefore, the debate on the constitutionalization of international law needs to be firmly situated within the context of domestic constitutionalism.Footnote ¹⁹ This is a precondition for a systematic analysis of what in essence remains (from a methodological point of view) an interesting hypothesis or research question. For, this is what the constitutionalization of international law is, beyond a mindset:Footnote ²⁰ a research question that seems to be of little consequence in practice. We all know that raising a hypothesis or asking a question is the basis for building a thesis. Yet, what we, international law lawyers, are missing is the tools that will enable us to actually try and answer that question, and validate or reject the hypothesis. What is a constitution? What is constitutionalism? Is there a constituent powerFootnote ²¹ in the decentralized structure of international law – other maybe than all states together (the idea of the international community) and nobody in particular? Can there be a constitution without a constituent power or demos? How is a constitution found in such a system? And what, after all, allows using the language of constitutional law for the international society, which is by no means akin to a polity? What would the function of a constitution be in the context of the international order and its society? Is there an added value in the use of the constitutional lens? In practical terms, what would/will it change if international law had/has a constitution? Would that make it more legitimateFootnote ²² or effective?

Moving then to the first critical comment, to duly frame the question on the constitutionalization of international law, we need to build a common understanding of what a constitution and constitutionalism are. The absence of such a consensus might explain why the language used lacks unity as to whether that constitutionalism is internationalFootnote ²³ or transnational,Footnote ²⁴ globalFootnote ²⁵ or pluralistic.Footnote ²⁶ It might also explain why De Wet,Footnote ²⁷ for instance, emphasizes normative hierarchy (which, as we argue in Section 4, is a point to which, under certain conditions, we agree) as a consequence of human rights, whereas FassbenderFootnote ²⁸ situates the constitutionalization of international law in the framework and organizational structure of international organizations,Footnote ²⁹ especially of the UN, the Charter of which is seen an a exhibition of constitutionalism. It might further explain why Dunoff and TrachtmanFootnote ³⁰ approach the question from a purposive, functionalist perspective that focuses on the function of the constitutional rules – leaving much to be complemented by practice, that would prove that, indeed, there is a commitment in the international community to lift those rules to the constitutional level. Be they thought-provoking and pointing to elements of international law of gravity, these approaches fail to establish common ground as to what are the essential constitutional elements of international law; in some instances, they mix positive law with normative aspirationsFootnote ³¹ (that is, the lex lata with the lex ferenda), but also, and most importantly, they miss the fundamental question of what makes these elements constitutional in nature – beyond what could be described as (an admittedly inflated) analogy or metaphor.Footnote ³²

The second objection has to do with disagreements regarding the impact and effect of those elements in terms of positive international law. An example is the idea of the verticalization of international law, through the establishment of normative hierarchies (linked to human rights), defended by many authors and (as already mentioned) explicitly perceived as an attribute of constitutionalism by De Wet,Footnote ³³ as opposed to the non-hierarchical, pluralistic vision of the international legal system defended, for instance, by Krisch.Footnote ³⁴ This disagreement is more than two different accounts of constitutionalization or a simple divergence in the way the two scholars perceive international law. Moreover, what these two opposing interpretations reveal goes beyond a merely different understanding of the ambit of human rights (i.e., pluralist v. universalist). Indeed, we may wonder if behind such a discrepancy over what is allegedly the same phenomenon, i.e., the constitutionalization of international law, certain (ideological) preferences are hidden, translated in selection bias regarding what the constitutional elements of international law are, but also how these ought to be conceived and interpreted.Footnote ³⁵ But it may also be that there is no truly empirically observable constitutionalization process, and that concept owes its very existence to scholar creativity, that is, to our “collective imaginary” that has constructed a notion using the language of constitutional law that needs now to be given legal content at the international level.Footnote ³⁶ Of course, the absence of a clear-cut distinction between positive law and normative aspirationsFootnote ³⁷ (a problem which is inherent to international law and its lack of centralization) adds complexity by giving scholars wider discretion as to what they can exclude or include in their own narrative of constitutionalization.

Thus, one cannot but agree with Kennedy, who perceives constitutionalization as yet another “project” next to other ones (one may think for instance of global administrative law, third world approaches, the process school, or even ‘New World Order’ and the global norms it identifiesFootnote ³⁸ – aspiring to provide ‘new thinking about how the global order coheres’).Footnote ³⁹ We wonder however if in the case of constitutionalization, rather than a common “tale”, there are disparate perceptions of it. It seems that international law is undergoing several constitutionalization processes at once, with the term acting as an all-encompassing “umbrella” with multiple meanings, and perceptions allowing it to host wide-ranging narratives. The common theme is that international law is changing with regards to its foundational rules, with globalization turning sovereignty thinner and these changes making its system more constitutionalized – whatever this may mean to each one of us.

3. Linking human rights to grand narratives of the international legal order

Having finished with this brief, critical account of the constitutionalization narrative(s), and declared our lack of competence as international law lawyers to confirm or reject it/them and, consequently, our critical “agnosticism” vis-à-vis it/them, we now move to the next step in our analysis, which aims at demonstrating that human rights are part of said narrative(s). The field of human rights is always in the background of several grand narratives of international law, but hardly ever at the foreground. We bring international human rights law to the foreground and take on claims about the role human rights play in particular in three grand “projects” of the international legal order, namely fragmentation,Footnote ⁴⁰ international legal pluralismFootnote ⁴¹ and, of course, constitutionalization.Footnote ⁴² Admittedly, human rights are assigned a role and occupy a privileged place within other narratives of international law as well. However, space contraints require that our brief discussion be limited to only those narratives that are comparable with and can be directly juxtaposed to constitutionalization. Our focus is the latter in an effort to highlight its links with human rights. Particularly, we wish to advance the claim that human rights law is an integral part to a constitutionalized reading of the international legal order, and in many respects serves to advance it.

The named three projects are comparable in that fragmentation and pluralism work as two sides of the same coin (fragmentation seen from “above” is pluralism seen from “below”),Footnote ⁴³ and both can work as a counter-narrative to constitutionalization (challenging its centralizing nature). But then pluralism can also be seen as constitutionalizing, at least as far as judicialized international law is concerned, in the sense that it contributes to more cross-fertilization, dialogue and cooperation between courts and their converging towards a central normative focal point.Footnote ⁴⁴

Scholars working on the grand narratives of international law seem to assume that human rights played a somewhat marginal role in projects of the international legal order, or, even when some more central role was given to human rights, it was never fully fleshed out. To articulate this assumption, it is necessary to first try to place human rights discourse in current narratives of the international legal order, and address what seems to be one of the biggest factors behind what can be described as a certain reluctance towards human rights in many of these projects, namely, the claim of human rights’ role in the hegemonic tendencies of international law, at least inasmuch as it advances an Euro-centric perspective on the values behind human rights law and law-making. Scholars aligned with the constitutionalization projectFootnote ⁴⁵ tend to look at human rights as indeed a very central part of their normative aspirations, particularly by looking at the reception and entrenchment of human rights in domestic legal orders and at the ways through which judicial and other institutions assert and protect human rights.Footnote ⁴⁶ In this sense, human rights law operates both as the cultural context (or the “entrenched” law necessary to the constitutionalist project) and as the background against which the entire project is built. Human rights is one of the ingredients of the constitutionalization narrative.Footnote ⁴⁷ The constitutionalist project also usually assumes some sort of charter of rights is a part of their project (even if scholars aligned with this project often fail to explore the content of any such charter)Footnote ⁴⁸ and suggests that international human rights law has the potential to become the “Grundnorm” of the international legal order.Footnote ⁴⁹ The reliance of this project on institutions is somewhat limited, as proposed by Kumm, whose idea of “cosmopolitan constitutionalism” is less dependent on institutionalism, while still relying on human rights as a fundamental normative aspiration of a constitutionalized international legal order.Footnote ⁵⁰

The fragmentation project, at least to the extent it is perceived as a counter-narrative to the constitutionalization project, is very critical of institutionalization, particularly with respect to human rights. For some, the ‘inchoate institutional character’ of international law is one of the greatest obstacles to a unified international legal order.Footnote ⁵¹ In a way, fragmentation tends to stick to a deceptively descriptive account of international law as a means to avoid committing to any sort of normative project. The problem is that this position in itself is normative.Footnote ⁵² Fragmentation, by being this empty shell, easily becomes prey to the status quo, only under new guise, through mechanisms like “strategic fragmentation”, but also others.Footnote ⁵³

Fragmentation, by being non-committal on the surface, tends to skirt accusations of participating in what Koskenniemi, referring to international human rights law, calls a hegemonic strategy of international law.Footnote ⁵⁴ According to him, international human rights law is an essential part of the hegemonic strategy to the extent human rights is an ideology and political project.Footnote ⁵⁵ The solution to the hegemonic strategy of international law seems to be, according to Koskenniemi, a return to formalism.Footnote ⁵⁶ This call to formalism finds followers also among scholars in the constitutionalization project, particularly Peters.Footnote ⁵⁷ This return to formalism seems to be the principal claim of the fragmentation narrative, particularly with respect to international human rights law. Of course, the main problem with it is that formalism does not avoid political commitments. It simply reinforces the status quo.

There are two ways to look at the relationship between international human rights law and the fragmentation of international law. From an internal perspective, the question is how different human rights bodies relate to one another, and how their different instruments are interpreted, especially in light of very similar (or identical) factual situations.Footnote ⁵⁸ From an external perspective, the key question is how international human rights law relates to other bodies of international law.Footnote ⁵⁹ The former perspective (or a version of it) is the most relevant for our current purposes (because we are trying to understand how human rights law operates endemically, even if on a domestic/international interplay), but a few words might be needed with respect to the latter.

Regional human rights courts have used “foreign” (that is, non-human rights) instruments extensively in expanding the scope and reach of rights protected under their constitutive instruments.Footnote ⁶⁰ The reason why foreign instruments have only been applied “indirectly” is because the Inter-American and European human rights courts have only the competence to declare violations of the American and European Conventions, respectively. Thus, because of their constitutive constraints, they are forced to “translate” all legal issues before them into human rights issues. This translation effort has two main effects: on the one hand, it promotes some sort of unity, by bringing all of international law under the human rights umbrella, which means to say that international legal norms are considered in light of their impact upon human lives (which is, arguably, the reason why law exists in the first place – to have an impact upon human lives). This unity further enhances the legitimacy of international human rights law. On the other hand, by bringing everything under the human rights umbrella, human rights courts create an informal or de facto hierarchy of international legal rules, putting human rights norms at the top of the pyramid. International human rights law affects the “systemic premises” of other areas of international law through this interaction,Footnote ⁶¹ with one consequence being a possibility for hierarchization. This consequence is, again, mandated by the constitutional constraints of these courts, and their popularity makes this hierarchization seem all the more pervasive, and it easily becomes part of the hegemonic project Koskenniemi is so critical of.

Finally, international legal pluralism lies somewhere in between the constitutionalization and fragmentation narratives (while challenging both) and echoes the constitutional pluralism debate in the European Union.Footnote ⁶² It ‘provides a normative vision of restructuring plural orders into pluralist ones – that is, re-envisaging them from fragmented, closed, sovereign legal orders into an open, interacting, interlinked, interdependent, multi-level structure of legal ordering.’Footnote ⁶³ However, it does not have the unification agenda and accepts a fragmented plurality of legal orders out of which none necessarily prevails.

The main perceived power of international legal pluralism is precisely to offer a counterpoint to the constitutionalist narrative, and a response to the dangers of constitutionalism, and also fragmentation: it is something of a positive spin on fragmentation focusing on the potential of a diverging legal order, as opposed to its apparent chaos. While fragmentation undermines international law, pluralism strengthens it,Footnote ⁶⁴ even if what looks like fragmentation seen from above can easily look like pluralism seen from below.

International legal pluralism generally lacks an overarching hierarchical structure, favoring the openness of different legal systems. Unlike constitutionalism's search for Grundnorm(s), pluralism accepts the notion that there is no such common point of reference.Footnote ⁶⁵ Pluralism can be either systemic or institutional, with the latter dealing with institutional viewpoints, whereas the former addresses more substantive issues across plural fora.Footnote ⁶⁶ In a way, it is a mirror image of institutional and systemic fragmentation.

The pluralist narrative seems to be the most apt to enable international human rights law and values to form an integral part of a project about the international legal order, alongside Kumm's ‘cosmopolitan constitutionalism’.Footnote ⁶⁷ But human rights courts seem to be more focused on the constitutional narrative, because that narrative privileges adjudicators, at least to the extent it mirrors domestic constitutional systems, which are anchored on judicial systems for their functioning. Additionally, how does the promise of pluralism (or cosmopolitan constitutionalism) react in light of the phenomenon of fragmentation of international law, which puts in evidence the difficulty of consistent interpretations of international legal norms across different fora? The (quasi-)adjudicatory practice of human rights bodies can contribute or become a hurdle to narratives of the international legal order.

The specificity of human rights law, which is (to give an example) connected to the way it is interpreted (evolutive or pro homine interpretation, as opposed to ordinary meaning),Footnote ⁶⁸ challenges the capacity of international human rights law being fully a part of general international law, seen as it chooses to play by its own rules. This idiosyncrasy is created by, and reinforces, the expertization and specialty of international human rights law,Footnote ⁶⁹ which is an important element in the fragmentation of all areas of international law. At the same time, though, the endemic practice of human rights institutions, and particularly of human rights courts, is to see themselves as playing a part in a constitutionalist project of international law, especially as they can often be perceived as engaging directly with domestic courts (even if they will reject the notion of being a “court of fourth instance”).Footnote ⁷⁰

4. The specialty of human rights: the impact of the internationalization of national constitutions on the system of international law

Having argued that human rights are interlinked with the constitutionalization of international law, the paper now turns to its main assertion, namely that the internationalization of human rights protection has helped the international legal order to develop certain systemic, “constitutional” features that mitigate the rigidity of the Westphalian structure.

In its general lines, the legal history of human rights in the West and its landmarks, the Magna Carta, the English Bill of Rights and the American and French revolutions in the era of Enlightenment, are well known. Gradually, human rights attained the form and strength of constitutional rights aiming to limit public power, but also to invite public authorities to develop policies to guarantee and enhance the well-being of the persons under their jurisdiction. That these bills of rights were included in the “basic” (to borrow the German term) law of a polity reflects their importance for the society and the idea that they are part and parcel of its constitutive/constitutional legal act and the social contract underlying it. Thus, apart from organizing power, the polity and the functioning of its institutions, national constitutions were also employed as a means to subject the acts and omissions of the polity's organs (governmental, but also beyond the executive) to the societal values that shape its public order, impose limits and preclude conducts that cannot be tolerated within it. This is a rough sketch of the national constitutional model in the West, we concede, but it should suffice for our present purposes.

The Second World War, its atrocities – and especially Shoah – came to prove in a tragic way the dramatic inadequacy of that model. Before the era of internationalization, flagrant human right breaches principally constituted a matter of municipal law, falling within (what nowadays seems to be) a sort of overstated domaine réservé. Protecting human rights at the national level alone had proven to be ineffective – especially where democratic roots were weak – allowing states to hide behind the veil of sovereignty and the prohibition of the interference with domestic affairs. Yet, to paraphrase Clemenceau, human rights are too important a matter to be left to national constitutions.

Human rights need to be effective. Their internationalizationFootnote ⁷¹ came just to address that very social necessity. However, that process required more than simply “copying-and-pasting” the rights one could commonly find in national constitutions. An area of law originally and in principle related to the relationship of the individual/citizen with public power had to be transplanted within a system originally and in principle regulating inter-state relationships. Thus, for constitutional human rights to be converted into international human rights, they had to be not only posited by the means of the sources of international law (such as treaties or custom), but also adapted to its systemic features. Their teleology and overall function have both remained unchanged. But, they now produce their effect within an entirely different context, society and legal framework. Consequently, the mindset changes too. This time, the scheme is rather oblique. States “promise” one another that they shall safeguard the rights of the human person. Thereby, they recognize the right of other states to lawfully react to violations – in principle – occurring within their national legal sphere. Hence, sovereignty becomes thinner, more transparent and states acquire a droit de regard, that is, the right to monitor human rights performance inside other states. The human being is still the primary beneficiary of the obligations at issue, but these are owed by the state to other states and also to the human being itself. The latter aspect is closely linked to the self-executing nature of human rights treaties,Footnote ⁷² allowing them to be invoked by the individual before domestic courts, as well as to the fact that certain instruments provide for control and establish international institutions – such as the UN Human Rights Committee, or the Inter-American Commission and Court – endowed with the competence to receive individual petitions for human right breaches.

However, the admittance of the human being as a recipient of rights directly at the international level could not leave the legal system unaffected. The study gives the example of three main changes in the systemic premises of international law, which partially owe to human rights as well. The first two stem from the erga omnes (partes) quality of human rights rules,Footnote ⁷³ whereas the third is linked to the principle of due diligence. The point made here is that the influence of human rights on the system of international law goes well beyond the obvious fact that the individual came to be added to the list with the subjects of international law,Footnote ⁷⁴ expanding thereby its span, and also bringing to an end the exclusiveness of states, which however remain the primary subjects of the system.Footnote ⁷⁵ These changes discussed below are of systemic, i.e. in a sense “constitutional” proportions.