An Interview With Esmé Shirlow on Judging at the Interface: Deference to state decision-making authority in international adjudication

What prompted you to write this book? What gap in our understanding of deference does the book fill?

This project grew out of my work in international adjudication, including my work as a government lawyer in the Australian Government’s Office of International Law. Through this work, I realized that many different approaches to assessing the role and relevance of domestic decisions in international adjudication have been classified as “deferential” (for example, the “margin of appreciation” doctrine, or “standards of review” analysis). However, the connection between these approaches—and how approaches differ either over time or before different international courts and tribunals—is less well understood. I also realized through working with different governments that it was also not well understood what different approaches to deference reveal about the nature and structure of international adjudication itself, including the relevance of deference to the “interface” between the international and domestic legal systems.

One of the cases I worked on during my time in the Office of International Law was the Philip Morris tobacco plain packaging claim. The issue of “deference” came up in quite disparate ways across that case. For instance, the High Court of Australia had ruled that the tobacco plain packaging measure did not result in an “appropriation” of Philip Morris’ intellectual property under the constitution, which meant that—had the case proceeded to the merits—the international tribunal would have had to consider whether the High Court’s ruling was relevant in any way to its decision about whether an “expropriation” of property had occurred under the treaty. Australia also asked the tribunal to defer to its policy assessments that tobacco plain packaging would be effective in cutting smoking rates. It submitted that it was for Australia—and not an international tribunal—to make public policy assessments of that type. This is just one of many international disputes which raise these questions around whether an international court or tribunal should defer to domestic decisions and, if so, how to achieve such deference. These are the types of cases and questions I investigate in the book.

In the book, I explore how adjudicators in four different international regimes (the Permanent Court of International Justice, the International Court of Justice, the European Court of Human Rights, and investment treaty tribunals) have approached issues of deference in 1,700 decisions concerning alleged state interference with private property rights across a 95-year time period (1924 to 2019).  I reviewed these decisions to identify instances where domestic decisions were referred to by international adjudicators and sought to identify whether the international adjudication deferred to these domestic decisions to give them some relevance; how they structured the giving of that deference; and the reasons they provided for giving deference to these decisions.

Based on this analysis, the book identifies a large number of techniques capable of achieving deference to domestic decision-making in international adjudication. I explore the function and manifestation of deference in international adjudication and what different approaches to deference in different times and contexts reveal about the nature of international law and its changing relationship to domestic legal orders.

In the book, you develop a taxonomy of deference that builds on different understandings of authority. In broad strokes, what are these different approaches to deference, and how do they relate or respond to domestic decision-making authority?

In Chapter 1 of the book, I define deference as arising in situations in which international adjudicators recognize the decision-making authority of domestic officials. Specifically, I argue that approaches to deference represent three different views as to the relationship between the decision-making authority of domestic and international actors. I refer to these as “conclusive,” “suspensive,” and “concurrent” approaches to authority and deference.

In “conclusive” approaches, one of the decision-makers is considered to have exclusive competencies or a form of supremacy over the other. Deference here operates as a controlling reason for an adjudicator’s decision. In the Philip Morris example, Australia’s view about the effectiveness of the plain packaging measure would take conclusive effect and be treated as dispositive of the question before the adjudicator. Such approaches to deference rely on principles of trumping to regulate interactions between domestic and international decision-making authority.

Other deference-achieving devices operate instead by according the domestic decision-maker some priority, suspending the capacity of the international adjudicator to determine the matter either at all or for a certain time.  Adjudicators using these approaches to deference avoid determining conflicting claims to authority by delaying or denying conflict; they analyze authority in “suspensive” terms.

By contrast, a third set of approaches envisage “concurrent” authority for both the domestic decision-maker and the international adjudicator. Adjudicators using these approaches view authority as conditional, and seek to balance or mediate—rather than override or foreclose—conflicting claims to authority. An international adjudicator might, for example, defer to a state’s claim that a public health measure will be effective, so long as that conclusion is shown to be “reasonable” or reached in “good faith.” Such approaches to analyzing authority lead to an analysis of deference along a spectrum (more/less deference). By contrast, the analysis of authority according to both the “conclusive” and “suspensive” structures prompts particularly categorical approaches to deference (defer/not defer).

Using this taxonomy, I argue that analyzing how a deference-achieving device operates is more important than assessing it by reference to its label. In fact, labels can obscure a lot. References to, for example, “justiciability,” “self-judging clauses,” or the “margin of appreciation” can describe reasoning that is actually structured in quite distinct ways. Using that insight, in the second part of the book I develop a taxonomy of approaches to deference in international cases by reference to how deference functions and is structured in practice rather than by reference to how it is labelled. The taxonomy is based on the difference between the conclusive, suspensive, and concurrent views of authority I’ve just outlined.

You compare investment arbitration tribunals to several other international adjudicatory fora. When it comes to approaches to deference taken by investment arbitrators, how does this regime compare to the others included in your study?

In the book, I make various comparisons between approaches to deference in the different adjudicative regimes. To take one example, the empirical analysis reveals differences between the particular approaches to deference preferred by adjudicators in each regime. The European Court of Human Rights (ECtHR) and investment tribunals, for example, disclosed a preference for relatively more conditional approaches to conceptualizing decision-making authority, viewing it as concurrent more frequently than adjudicators in the other regimes. The ECtHR adopted this view of authority in 82% of its observed applications of deference and investment tribunals in 73% of applications. The  Permanent Court of International Justice and International Court of Justice, by contrast, adopted a concurrent view of authority in only 45% and 55% of observed applications of deferential reasoning. They displayed a greater tendency than adjudicators in the other two regimes to apply modes of deference reflecting conclusive or suspensive views of authority. In the book, I suggest that these different “profiles” reveal differences in how each of these adjudicators conceptualizes the interface between domestic and international decisions (and the domestic and international legal systems), as well as differences in institutional and procedural design. Investment treaty tribunals, for example, disclose an overall more mixed profile to structuring deference relative to other adjudicators, which is perhaps to be expected given the ad hoc nature of that adjudicative regime.

Another interesting finding emerging from the analysis is that international adjudicators frequently pierce the state’s veil in analyzing whether to defer to domestic decision-makers. As I explore in the book, this impacts how these adjudicators consider and appraise state decision-making authority, and impacts the specific approaches to deference that they adopt in practice.

Have modes of deference deployed in ISDS cases changed significantly over time? If so, what do these changes tell us about the development of the regime?

Previous studies of deference have treated it as a fixed phenomenon and have rarely considered its dynamic qualities. So, it was important for me in the book to investigate whether—and if so how—deference changes over time. Overall, I found through the empirical analysis that deferential reasoning has become more frequent over time. Across the four regimes, applications of deference in majority decisions peaked between 1984–1989 and again in 1993–1995. Applications of deference began to rise once more from 2004 onwards, dropping off again in more recent decisions. Since 2011, however, international adjudicators have applied some form of deference on average once in each majority decision.

Using this temporal analysis, I make various comparisons between the different regimes in the book. For example, I note various differences in the tendency of investment arbitrators—compared to judges at the ECtHR—to adopt “substantive” versus “procedural” approaches to deference. I also show changes over time in how authority is being analyzed in the various regimes. For example, whereas the approach of the ECtHR shows a strong preference for concurrent approaches to authority (averaging 71% of applications from 1975–2019; and 80% from 1990–2019), this preference appears less strong for investment tribunals (averaging 50% of applications from 1990–2019, but 70% from 2008–2019). The temporal analysis also shows that approaches to authority (as concurrent or as categorical/suspensive) began to diverge in investment arbitration decisions from 2005–2007, whereas they diverged earlier in the decisions of the ECtHR (1991–2001).

These temporal findings reflect evolutions in how adjudicators are analyzing the domestic/international interface, including in response to broader debates about their role vis-à-vis domestic decisions and ongoing reforms to their institutional features. Adjustments to the jurisdictional competences of international adjudicators will, for instance, impact their relative legitimacy and expertise vis-à-vis states. As adjudicators become more acquainted with particular types of disputes, their authority to deal with them may also improve. Procedural adjustments may similarly impact deference. Party appointments of arbitrators may introduce particular skills, knowledge, or legitimacy to the panel deciding a given dispute. Such adjustments will impact the balance of authority between adjudicators and domestic officials and thus the likelihood—and structure—of deference in a given case.

What lessons does your analysis hold for government officials working in areas that may find themselves at the “interface” of domestic and international authority?

The book aims to assist government officials to navigate complex questions about deference as litigants, policy-makers, and as creators and reformers of international courts and tribunals. It aims to shift the discussion from the identification of decisions or particular approaches as deferential or non-deferential, to a more specific and nuanced enquiry in order to assist litigants to frame their submissions on deference in specific cases. In essence, a key message is that approaches to deference are necessarily malleable, which opens up scope for litigants to be quite creative in crafting their pleadings to bring in (or exclude) deference in a given case. The final chapter of the book develops a framework to guide this exercise, presenting what I call “levers” for deference that litigants can use to increase or decrease the relevance of deference in their own submissions.

In addition to providing this guidance for litigants, the book also highlights how officials might structure their own domestic decision-making processes and outcomes to maximize the chances of their decisions attracting deference from actors like international courts and tribunals. The book also offers insights into how the design of international courts and tribunals and reform processes might influence the propensity of different courts or tribunals to adopt different approaches to deference.

You mention state submissions to the UNCITRAL WGIII in Chapter 10. In what ways are the approaches to deference discussed in your book relevant to attempts to reform ISDS?

The book addresses several themes of relevance for ongoing discussions about the reform of particular adjudicative regimes, including UNCITRAL WGIII’s work. The book illustrates the value of examining deference conceptually and systemically for what it reveals about international adjudication and the international/domestic interface.

As I show in the book, ostensibly technical debates about deference reflect more fundamental debates about the appropriate balance between the decision-making authority of international and domestic actors.  In the book, I argue that the question of whether deference should or shouldn’t apply in a given regime is not the right question: deference is an inherent component of international adjudication. It is instead more productive to ask how deference should be structured and applied. I argue that deference is necessarily malleable, so “fixing” or directing approaches to deference is unlikely to be a feasible (or desirable) reform option. However, I show how reforms to the features of international courts and tribunals will impact approaches to deference. Approaches to deference depend heavily upon how international courts and tribunals conceive of their role, legitimacy and expertise relative to that of domestic actors. This indicates that deference is likely to differ depending on a range of factors, including historical context, geographical factors, the background and skills of adjudicators, the claim structure and caseload of international courts, and the procedural features of international courts and tribunals. Many of these features are currently open for discussion and reform, including as part of the WGIII reform process. In this sense, the book illustrates just how interconnected individual reforms to international courts and tribunals can be, including to show how even exclusively procedural reforms can have far-reaching substantive implications.


Esmé Shirlow is an associate professor at the Australian National University’s College of Law and maintains a practice in public international law and investment arbitration.

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