Introduction: a circle of concepts: nature, custom, stipulation

Philosophical jurisprudence, from Plato to Hans Kelsen, rests upon three fundamental concepts of order and three allied concepts of law: the order intrinsic to human nature grounds the natural law, the order found in informal social practices grounds the customary law, and deliberately stipulated order grounds enacted law. As with many sets of foundational concepts, these are often defined or at least described in terms of each other. This set of analogies and disanalogies between nature, custom, and deliberate stipulation forms the deep structure of traditional philosophical jurisprudence: they are the conceptual lenses and tools by which philosophical analysis of law has proceeded. The history of philosophical jurisprudence reveals how rare it is to examine the lenses by which we see and the tools by which we dissect.

Sometimes customary habits are compared to natural instincts because they operate spontaneously, automatically, and tacitly. Custom here means a kind of second nature: our customary habits operate as unobtrusively as our breathing. In this sense, custom is like natural instinct except that it is learned in a particular social context. Yet custom is also described as a set of informal conventions, a set of practices of social coordination that arise from informal agreements without being imposed by enacted law. Custom here is an unwritten law: customary conventions differ from enacted conventions only by not being deliberately imposed.

Custom, in short, must be analyzed into two more basic notions: habit and convention.

Although the worlds of Vitoria and Suarez were remote from our own, some of the problems these authors faced resemble ones that still concern modern jurists and political philosophers; and these problems involve not only the content of international law but also its grounding in custom or natural law or positive enactments. In this paper I want to suggest that Vitoria displayed considerable versatility in deploying various norms of international law – or even in inventing such norms on occasion – but without any serious concern for the grounding of these norms, whether in custom or in some other source. Suarez, on the other hand, coming two generations later, presented a detailed account of the sources of ius gentium within a massive synthesis that included full-scale treatments of natural law and customary law.

Past and present

Anthony Pagden has warned us against studying earlier ideas on international law with present-day concerns in mind:

Such statements are of course platitudinous among historians. It is precisely the specificity of a past situation that we need first to understand.

Introduction

In December 1812 things seemed to get out of hand in the legal faculty of Berlin University. Its most celebrated jurist, the aristocrat and leading light of self-confident metropolitan Prussian culture, Friedrich Carl von Savigny, threatened to resign from the faculty. It is hard to overestimate the weight of this threat. Since his early masterpiece, Das Recht des Besitzes (On the Rights of Possession), Savigny had been hailed the new pontiff of Roman Law. His students admired him endlessly, some even likened him to Christ. And, if ever this Olympian was to throw his high-born contempt at someone, the object of Savigny's anger would surely have had to play possum – or so it seemed. Not so Eduard Gans: this offspring of a Jewish banking family had originally attempted to join the faculty of law in Berlin, but at Savigny's instigation he was denied the possibility, arguably because of his Jewish background. Gans had originally been confident that he could rely on the Prussian emancipation edict of 1812, but Savigny had written his reports to the Prussian ministry of culture arguing for the impossibility of appointing a Jew to the law faculty, and, at some point, the relevant passage of the emancipation edict was rescinded by royal cabinet order, on request, of course, of the influential faculty of law. Because of these events, it was not hard to guess what kind of enemy Gans would become.

The sack of Tienen

On 8 June 1635, a Franco-Dutch army, under Stadtholder Frederick Henry (1625–1647), arrived before the town of Tienen. Three weeks earlier, the French had entered the Spanish Netherlands and had joined up with the Dutch troops of Frederick Henry. Now, the joined forces had begun their march towards Brussels.

The purpose of the invasion was to drive the Spanish from the Netherlands. Pamphlets were circulated to exhort the people of the Spanish Netherlands to rebellion. The small town of Tienen was part of the first line of defence of Brussels. A Spanish force of 1,200 men under Captain Martino de los Arcos, well supplied with arms and ammunition, was there to defend the town.

Upon his arrival, Frederick Henry sent a trumpeter to summon surrender. He promised the burghers of Tienen their liberties and the practice of their religion. Without consulting the town magistrate, Captain De los Arcos refused. He stated that ‘the arms of his Majesty were in town and that it was not customary in such circumstances to surrender a place or town without having seen and heard one another, as both had powder and ammunition’. The next day, the trumpeter made two more appeals; twice he was turned down. Meanwhile, De los Arcos promised the town magistrate to surrender after the first skirmishes.

Surprisingly, there were no skirmishes before the main assault. Around 1.30 p.m. the enemy artillery opened fire and 6,000 men started the attack.

As historians of law have long recognized, Gratian's Harmony of Discordant Canons, commonly known as the Decretum, is a foundational text for modern Western jurisprudence. Even though this text presents many interpretative difficulties, in part because it has almost certainly been altered and expanded in a variety of ways, its main purpose is clear enough. That is, as the title indicates, it represents an attempt to show how the diverse and seemingly inconsistent canons of the church can be interpreted and applied in a consistent way – in a word, harmonized. In the first twenty distinctions of the Decretum Gratian sets forth the general principles governing the interpretation of laws. (Thus, modern commentators often refer to these distinctions as the “treatise on laws,” a usage I follow.) While these distinctions do not comprise a fully worked out theory of law, they do set forth a coherent conception of law developed in what was to become the preferred scholastic way – that is to say, through the selection and interpretation of authoritative texts, here including copious citations from patristic sources and Isidore's Etymologies as well as legal texts properly so called.

The Decretum begins as follows:

‘Is it a custom?’ the visiting Horatio asks Hamlet after hearing ordnance shot off. Hamlet replies that it is (‘Ay marry is't’), but says that ‘it is a custom more honoured by the breach than the observance'. This paper considers the relationship of custom to what is honourable, moral, the right thing to do. Hamlet's claim can be taken in two distinct ways. Is he making the descriptive claim that people don't actually follow the custom that much, honouring it more by breach than by observance? Or is he making the prescriptive claim that although it is the local custom it would be more honourable to breach it than observe it? The context makes the latter much more likely, not just because of Hamlet's general attitude but because of the particular way that he introduces his claim. He says, ‘But to my mind, though I am a native here and to the manner born, it is a custom …’ Although to the manner (manners; custom) born, he has his own oppositional mind. There is what people generally, the natives, find honourable, which is to fire the cannon when the king drinks. And then there is what Hamlet himself finds honourable, which is not to engage in such frippery. For Hamlet, what people conventionally find right, and consequently conventionally happens, is not what is really right. Or at least, uncertain as he is, he entertains the idea.

A book on customary law, many modern lawyers might say, can have no relevance for them. And neither, many modern thinkers would echo, could it be of much interest. On many influential modern accounts, reliance on customary practices is a mark of inadequacy: acceptance of customs should be minimal and provisional since an unreflective attachment to customary ways of thinking is inimical both to practical thought and to political harmony. Modern societies and their legal systems depend not on enslavement to customary habits and laws but on reasoned principles and doctrines; customary laws grow up only where legislators have done a particularly poor job, leaving a need for elaborate statutory construction and legislative gap-filling. The more coherent and consistent a legal system, the less the need for such customary rules and practices: an interest in customary law reflects at worst what Jeremy Bentham called the ‘sinister’ interests of self-interested reactionaries, and at best the eccentric tastes of scholars, antiquarians and those purporting to be international lawyers who work in what, on such accounts, is really a lawless international world.

This brief chapter introduces the diverse views of customary law offered in this collection of essays, showing how, despite this diversity, the thirteen contributors are united in arguing that such rejections of the relevance of customary law are wrong.

The common law has long been explained as a customary system of law, rooted in consent, whose rules are both consonant to reason and flexible, allowing the law to develop in accordance with the ‘felt necessities’ of the community. As such, it seems to have much in common with a law of nations founded on the consent of nations as well as reason, manifested in part by developing customary practices in the international community. Indeed, lawyers have gone so far as to state simply that the law of nations is part of the common law. In the words of Lord Denning:

Yet such a view has not been universally subscribed to. Many judges have taken a narrower approach, requiring norms of international law to be positively incorporated before they bind at common law. Nourse LJ, for instance, felt that established rules ‘derived from one or more of the recognised sources of international law’ are binding only when they have ‘been carried into English law by statute, judicial decision or ancient custom’.

Much has been written on the legal status of customary law, but considerably less attention has been devoted to the question of determining the content of the customary law whose legal status (or not) is at issue. Like any other source of law, customary law presents the question of interpreting, applying, and enforcing the emanations from that source, but interpreting customary law – or interpreting the custom that is to be part of the law – presents issues arguably more complex than those presented when we are considering the interpretation of constitutions, statutes, regulations, treaties, and even the common law. My goal here is to explore these interpretive questions, and to do so with perhaps somewhat of a skeptical attitude. This is not to say that such skepticism will turn out at the end of the day to be justified. It is to believe, however, that addressing such skeptical questions is an inevitable task for any satisfactory account of the role of customary law in common law adjudication, and perhaps to an even greater extent with respect to the role of customary international law as a part of international law more generally. So, although in this paper I will ask more questions than I answer, my goal is to put on the table those interpretive issues that anyone seeking to develop a theory of customary international law, or a theory of the role of custom in common law decision-making, must at least attempt to answer.

International law is a system of customary law. And, like all writers of textbooks on customary law, scholars of international law find themselves in a curious position: it is philosophically impossible to treat customary law as a system of clear, settled rules since there is no way of settling the correct text or formulation of those rules. As Brian Simpson writes in an essay on English common law,

What is true of English law is at least as true of public international law, on which not only academics and individual judges but also tribunals and courts disagree, similarly often at inordinate length.

This essay argues that one of the most fundamental differences between various treatises on international law stems from diverging assumptions about what renders a statement of a rule of international law correct or authoritative.

Some of the extreme opacity of the idea of custom seems to be owed to two considerations. One is that custom modifies the actors who observe it; a well-established custom is not merely a constraint external to a person's character, but has a tendency, with time, to constitute an aspect of his being. Another is that customary arrangements have typically involved an interaction between two overlapping groups of people: the community within which given customs are observed and a much smaller group perhaps most neutrally described as the custodians of such arrangements, a group who are in practice charged with the articulation of the customs, and therefore with their application and development. A link between these two considerations is that the very function of the custodians is likely to demand internalisation of methods, moral attitudes, and intellectual habits appropriate to the social norms that they articulate. At all events, these generalities were true of the pre-modern common lawyers. From the perspective of a book on custom, the interest of pre-Benthamite common law thinking lies in the tension it exhibited between its accounts of what the lawyers did – the patterns of thought and behaviour that might be said to constitute a trained professional – and its attempts to identify their esoteric practice with principles engendered by the wider population.

In 1982, in his monograph on custom in the Middle Ages, the Belgian scholar John Gilissen remarked on the lack of studies in English concentrating on the subject. The situation has not improved significantly. Apart from two articles by Albert Kiralfy and one by Paul Brand, such attention as has been given to the topic has been concerned with particular customs, especially manorial customs, borough customs, and the custom of merchants. The present paper will not fill this gap, but will try to set the uses of the idea of custom in England against the better-studied continental background.

Custom in Roman law

Although the part played by custom, consuetudo, in Roman law is outwith the scope of the present paper, many of the ideas found in the Middle Ages were rooted in Roman soil. It cannot therefore be wholly ignored. Two texts in particular were influential, one in the Digest attributed to Julian, but generally regarded as having suffered some post-classical or compilatorial alteration, and one in the Code ascribed to Constantine. Out of these texts, together with some others of less central importance, we may distil a number of points. First, stress is laid on the long-standingness of a practice: it is referred to, for example, as inveterata, longa, or diuturna. Secondly, it is described as flowing from the (tacit) agreement of the people. Thirdly, it is unwritten, contrasted with written lex. Fourthly, it may or may not prevail over a contrary lex.

A troubled concept

“Custom is not a special department or area of public international law: it is international law.” So writes Ian Brownlie; yet, writers on international law now widely declare customary international law to be dead or at least in mortal crisis. Such disputes over its viability, of course, stem from differences of political principle and partisan geopolitics, but they also stem from genuine confusion about the nature of custom and its role in the international legal order.

For example, according to the International Court of Justice, it is “axiomatic” in international law jurisprudence that customary international law is found “primarily in the actual practice and opinio juris of States.” To determine whether legally recognized custom exists on some matter, the Court added later:

What is here said to be axiomatic in international law jurisprudence is the familiar additive understanding of custom: custom is analyzed into behavior or usage (usus) plus belief or conviction of (legal) necessity (opinio juris sive necessitatis).