If international law books come with prefaces, it is usually not by virtue of a demand from the potential readership but because authors relish speaking about themselves and the history of their work. Prefaces are even places commonly meant for authors of international law books to indulge in some well-engineered sentimentalism. This is not surprising. Having courageously fought their way to completion of a decent manuscript and having juggled academic writing with the pressure of a constantly accelerating profession, authors of international law books often finish their work with the feeling of being miserable heroes. In fact, I have regularly come to think that completing a book in the twenty-first century requires the skills of an armchair paratrooper who can intrepidly, dedicatedly and frenetically read, think and write in any moment clear of teaching, administration and management. And yet, whatever the heroic feat of completing a book under such conditions possibly is, it often remains unclear to any such hero what international law books actually contribute to in the distressingly burning world which such books seek to describe, evaluate or manage. If the story of authors of international law books is a story of miserable heroes, we can probably forgive them for the sentimentalism they manifest in their prefaces.

Whatever sentimentalism the rest of this preface may thus betray, this book does not grapple with the sentiments of international lawyers. Rather, it deals with their beliefs. It particularly develops the idea that international lawyers – whether as scholars, judges, counsels, militants or teachers – engage with the problems of the world through the deployment of a belief system. According to the heuristics built in this book, being an international lawyer entails the membership to a belief system. This belief system is manifest in the way in which fundamental doctrines – around which international legal discourse is built – operate in international legal thought and practice. Fundamental doctrines of international law, this book argues, create the conditions of their own existence, such self-referentiality guaranteeing a comfort space where international lawyers have to justify neither their fundamental doctrines nor their use thereof when they describe, evaluate or manage the world.

The claim that international law bears the characteristics of a belief system certainly does not amount to belittling international law. Quite the opposite. Belief systems are very serious matters, especially when they are used to describe, evaluate and manage the world. Although the heuristic exercise conducted in the following chapters falls short of any nihilism or utter scepticism, I am aware that my claim could raise the question of a possible rupture with my earlier work on sources, statehood and responsibility. I acknowledge that despite my long interest in unearthing the architecture and politics of international legal argumentation, much of my earlier work engaged with international legal arguments in their own terms and especially in terms of sources and interpretation. In contrast, the following chapters extend an invitation to all international lawyers to ‘unlearn’ their knowledge and sensibilities regarding the formation and functioning of the fundamental doctrines, which includes a radical break from international lawyers’ common representations of their fundamental doctrines in terms of sources and interpretation.

Whether the discussion offered in this book possibly constitutes a discontinuation with my previous work is irrelevant. This is not only because I have always been amused by the descriptions of my earlier work as ‘positivist(ic)’, for I do not even know what positivism is other than being a convenient strawman in a confrontational and deliberative business. Mainly, questions of continuity or discontinuity are unimportant because I am convinced that consistency of thoughts is overrated in the discipline of international law. Actually, the obsession with consistency of thoughts is something which I have always found very bizarre in a discipline which considers itself intellectual. Thinking must entail a readiness to vandalise one’s early thoughts. This does not mean that the suspension of the belief system advocated in this book repudiates anything I have done earlier – it should remain possible to research international legal argumentation from within the belief system. The point made here is rather that it is time to bring an end to the impoverishing social expectation that each international lawyer constantly and invariably abides by the same one-dimensional concept of international law.

The foregoing should suffice to indicate that this book is not meant to belong to (and vindicate) any ‘tradition’ or ‘school’ of legal thought. Whilst there is some didactic convenience of segmenting international legal thought in strands, this book turns a blind eye to such conventional subdivisions. This is why it unashamedly borrows from a wide variety of legal scholars, philosophers and social scientists without much interest in the theory or tradition with which they are associated and irrespective of the cross-commensurability of their respective arguments. Instead, I simply use the thoughts of these authors as conceptual tools to design my own thoughts, without seeking to import their respective theories in international legal thought. This purely instrumental approach inevitably transforms and deforms the thoughts of others. This will probably be held against me anyhow. I remain convinced, however, that innovative thinking comes at this price.

Thinking is an experiment. The experimentation that led to the claims developed in this book started a few years ago and benefitted from the decisive support and critical input of some key colleagues and friends. They ought to be mentioned here as they have generously and repeatedly allowed me to bounce half-baked ideas off them whilst also reading parts of the manuscript. In this respect I would like to express my immense gratitude to John Haskell, Akbar Rasulov, Sahib Singh, Justin Desautels-Stein, Geoff Gordon and Yannick Radi. Thanks to their continuous availability and interest, they have offered me a remarkable and permanent sounding board for my ideas throughout this project. I will always be indebted to them. The following chapters explicitly indicate when my exchanges with them have directly informed my reflection. I am hugely indebted to Pierre Schlag, who provided me with extensive feedback on several occasions and who spent hours with me discussing several facets of the argument during a visit at the School of Law of the University of Colorado. Pierre generously accepted to write the Foreword of this book. I am not only appreciative but also humbled that this book is introduced by one of the greatest and most refined legal thinkers of the twenty-first century. I am immensely grateful to Georg Nolte, Heike Krieger and Andreas Zimmermann for inviting me to spend a sabbatical semester in Berlin between September 2016 and February 2017, which provided me with the space and time necessary to finalise this book. I thank Jan Klabbers, Steven Wheatley, Janne Nijman, Catherine Brölmann, Gleider Hernandez, Luíza Leão Soares Pereira, Maruša Veber, Dimitri Van Den Meerssche and Maiko Meguro, who expressed interest in the project and whose repeated feedback and recommendations were very insightful. I thank Rosa Beets, whose research assistance proved enriching, especially regarding the discussion of the fundamental doctrine of statehood. I am very thankful to Richard Clements for his tremendous assistance at the copy-editing stage. As always, Finola O’Sullivan and Larissa van den Herik at Cambridge University Press have been wonderful and patient advisors during the maturation of this project.

Thoughts are inevitably refined through debates. I am grateful to the conveners, participants and funders of the numerous workshops where parts of the argument developed in this book were presented and debated over the last two years. I can only mention a few of them here. For a workshop at the Mississippi College School of Law in May 2015, I would like to thank John Haskell. For a workshop at the Instituto Tecnológico Autónomo de México (ITAM) in Mexico City in November 2015, I would like to thank Alberto Puppo, Jorge Cerdio and Máximo Langer. For a workshop at the Amsterdam Centre for International Law (ACIL) in January 2016, I would like to thank Ingo Venzke, Catherine Brölmann, Roland Pierik and Markos Karavias. For a workshop at University College Dublin in March 2016, I would like to thank Richard Collins, John O’Dowd, Gavin Barrett, Imelda Maher and Claire Hill. For a workshop at Sciences Po Paris in March 2016, I would like to thank Diego Fernandez Arroyo, Horatia Muir Watt and Mikhaïl Xifaras. For a workshop at the Faculty of Law of the University of McGill in March 2016, I would like to thank Cassandra Steer, René Provost, Frédéric Megret and Ivana Isailovic. For a workshop at Colorado Law School in April 2016, I would like to thank Michael Zaccaro, Justin Desautels-Stein, Pierre Schlag, Tiago Guevara and Emilyn Winkelmeyer. For a workshop at Temple University in April 2016, I would like to thank Duncan Hollis, Pam Bookman, Jeffrey Dunoff, Meg deGuzman, Jean Galbraith, Mark Pollack and Brishen Rogers. For a workshop at the VU Amsterdam in April 2016, I would like to thank Geoff Gordon, Wouter Werner and Gareth Davies. For a workshop at the Erik Castrén Institute of International Law and Human Rights at the University of Helsinki in April 2016, I would like to thank Jan Klabbers, Martti Koskenniemi, Sahib Singh, Mónica García-Salmones and Walter Rech. For a workshop at the School of Law of the University of Glasgow in May 2016, I would like to thank Akbar Rasulov, Christian Tams, James Devaney and Gail Lythgoe. For a workshop at the School of Law of the University of Durham in May 2016, I would like to thank Gleider Hernandez, John Linarelli, Ruth Houghton and David van Rooyen. For a workshop at the Université Libre de Bruxelles in June 2016, I would like to thank Olivier Corten, François Dubuisson, Anne Lagerwall and Martyna Fałkowska. For a workshop at the European University Institute in November 2016, I would like to thank Dennis Patterson, Nehal Bhuta, Dimitri Van Den Meerssche, Emmanuel De Groof and Stavros Pantazopoulos. For the possibility of delivering a Thomas Franck Public Lecture at Humboldt University on the topic of this book in February 2017, I would like to thank Georg Nolte, Heike Kriege and Andreas Zimmermann, as well as all the attendees, including Christian Tomuschat. For a workshop at the Ghent Rolin-Jaequemyns International Law Institute at the University of Ghent in February 2017, I would like to thank Tom Ruys. For a presentation at the University of los Andes in Bogota in March 2017, I would like to thank René Fernando Urueña Hernández as well as Vanessa Suelt Cock. For a presentation at the University of Tokyo in March 2017, I would like to thank Koji Teraya, Kazuhiro Nakatani and Maiko Meguro. For a presentation at Waseda University in March 2017, I would like to thank Shuichi Furuya and Yota Negishi. For a presentation at the University of Kyoto in March 2017, I would like to thank Shotaro Hamamoto, Mari Takeuchi and Yohei Okada.

Even for armchair paratroopers such as international lawyers, support and friendship are invaluable. I am thankful to my friends and colleagues at the Manchester International Law Centre and the Amsterdam Centre for International Law for their continuous support. They include my friends and colleagues Iain Scobbie, Yenkong Ngangjoh Hodu, John Haskell, Shavana Musa, Philip Burton, Mariela Apostolaki, André Nollkaemper, Ilias Plakokefalos, Markos Karavias, Ingo Venzke, Janne Nijman, Catherine Brölmann, Kathryn Greenman and Maiko Meguro. As for my previous books, I would like to express my immense gratitude to my friend Alain Brouillet, whose passion for international law books and generosity have allowed me to have at my disposal one of the richest collections of classics of international law rarely privately owned by an international lawyer. I am similarly grateful to Liliane and Christopher Fawcett for providing me with inspiring retreat environments for my reading and writing for several years. Last but not least, I would like to mention – but not name – those most cherished daily supporters without whom even the very little that can be achieved through an international law book would not have been possible. While hiding my passport or lamenting my departure when time to go to the airport came, they have always sarcastically been smiling at the very surreal job all those who can possibly read this preface are engaged in. Thinking about international law and its fundamental doctrines with a bit of distance would not have been possible without their sarcasm and their constant reminders that the real heroes in this world are not international lawyers.