The Forgotten Foundations of Constitutional Law 

Editor’s Note: This is Part I of a two-part series.

When commentators today speak of the “rule of law,” they usually have in mind something quite recent: a body of liberal-democratic principles secured by written constitutions, separated powers, and courts willing to strike down legislation that strays beyond constitutional bounds. The framing is understandable, since these institutions are the visible furniture of modern constitutionalism. But it is also misleading. The intellectual scaffolding on which our constitutional inheritance rests was built long before the Enlightenment, by traditions that are now largely forgotten by those who use the language of constitutional government most freely. 

Sir William Blackstone once observed that “Christianity is part of the laws of England.” Although this statement struck the mind of Thomas Jefferson as a kind of “judicial forgery,” Blackstone was expressing an idea that was commonplace among English lawyers. The question is not so much whether Christianity is part of the common law, but what parts and in what respects it is, or has been, integral to the body of law as a whole. And what can be said of the common law in general can also be said of constitutional law in particular. Certain important parts of our contemporary inheritance of constitutional law have been shaped decisively by Christian beliefs, practices and institutions, and the whole body of constitutional law, in its variegated national forms, reflects numerous specific Christian influences. 

Christianity is not, of course, the only influence on the common law and on constitutional law in particular. Many interweaving historical influences have shaped modern constitutional law. Among these, four broad strands stand out as especially influential: Greek philosophy, Roman law, Christian theology, and Enlightenment principles. While the exact contribution that each of these has made—and should continue to make—is a matter of debate, there is little doubt that each has contributed substantially to how constitutional law is conceived and practised in our day.  

Greek philosophy introduced a taxonomy of constitutional types and the concept of the rule of law. Roman law contributed the crucial notion of jurisdiction, a fundamental aspect of contemporary constitutional law. Christian theology provided a framework that qualified the authority of civil government by a higher natural or divine law, with the church’s spiritual authority placing practical limits on temporal powers. The powers of civil and ecclesiastical rulers were tempered through various means, including the administration of oaths of office and the issuing of charters guaranteeing the rights of religious, social, economic, and civil associations of many kinds. And while the Enlightenment is rightly associated with the modern principle of the separation of powers and the establishment of written constitutions enforced by judicial review, these principles also owe much to practices established prior to the Age of Enlightenment, especially those developed and extended during the Reformation. Despite important Greek, Roman, and Enlightenment contributions, constitutional law would not be what it is today if it were not for the influence of Christianity. 

Greek Philosophy and Roman Law 

The term “constitution” can designate either a description of the institutions and powers of government established in a political community or a prescription of what institutions ought to exist and how they should operate. Aristotle took an initially descriptive approach when he distinguished several kinds of politeia (constitution, regime) based on whether a political community is ruled by one, few, or many persons. Also intrinsic to his analysis was an assessment of whether such rulers govern in their own interests or for the common good. The result was six fundamental types of constitution: monarchy, aristocracy, and polity—when governing powers are exercised for the common good—and tyranny, oligarchy, and democracy when they are exercised in the interests of the governors. Aristotle’s analysis was descriptive insofar as it offered a method of classification of constitutions, but it also offered a moral evaluation of those systems on the basis of the ends for which governmental power is employed. 

A further dimension of constitutional law concerns its status as law, and its relationship to the rule of law. Aristotle raised this issue when he asked whether it would be better to be governed by a good ruler or by good laws. The advantage of governance by wise and virtuous rulers is that they are able to govern in a manner that is responsive to specific circumstances and changing conditions. The advantage of government by good laws is that this makes it difficult for bad rulers to govern in their own self-interest. Aristotle seems to have considered that the absolutely ideal form of government is monarchical rule by a wise and virtuous individual. However, he recognised that for many political communities the best constitution will realistically involve a mixture of oligarchy and democracy tempered by the rule of law. 

What is “the rule of law”? At a minimum, it could mean governance through the promulgation of general rules. But it might also mean that those who rule and the powers they exercise are themselves controlled and defined by law. Here the Roman law concept of iurisdictio has played a key role. In its broadest sense, iurisdictio referred to the authority to administer justice. In Roman law, a general power of jurisdiction was conferred on all higher magistrates (magistratus maiores), whereas magistrates of lower rank (magistratus minores) had only limited jurisdiction. In a territorial sense, iurisdictio also referred to the districts over which magistrates were authorized to exercise authority. The term therefore came to designate the administration of provinces under governors in the Roman Empire. Conceived this way, governing authority was capable of being legally defined. The rule of law might mean not only governance through law but also governance under law. 

In a Roman imperial context, the idea of particular and limited jurisdiction applied to subordinate officials like magistrates and governors. Although the emperor was formally bound by ius publicum (public law), this had diminishing practical effect, especially as more and more offices and powers were consolidated in the emperor’s hands. Roman law was soon replete with references to the virtually unlimited power of the emperor, derived in theory from the people but increasingly absolute in practice. The rule of law could not apply to the emperor unless he was understood to be exercising a delegated authority under a law to which he was subject. Greek and Roman thought had imagined a kind of law that might possibly fulfil this role, such as when Aristotle distinguished between the particular laws adopted by each political community and the general laws recognized by all people in accordance with nature, and when Cicero proposed that “true law” is that which is in accord with nature, and that this “one eternal and unchangeable law” is “valid for all nations and all times.” 

Christian Theology 

It was St. Paul who expressly applied these propositions to all political authority as a matter of principle, when he said that rulers are “servants of God” responsible to administer divine justice. Saint Peter similarly taught that while Christians ought to be submissive to kings, governors, and other rulers, their ultimate allegiance must be to God rather than men. This gave rise to charges that the early Christians were “acting against the decrees of Caesar, saying there is another king, Jesus.” The Caesars had increasingly asserted the prerogatives of deity, proclaiming themselves to be gods. Under the influence of Christian teaching, however, later Roman emperors “abandoned their claim to be true divinity on earth and recognized instead in God the origin of their power.” As early as the eighth century, kings and emperors were expected at their coronations to swear oaths that they would, among other things, execute justice and mercy in their judgments, and later, that they would govern in alignment with the established customs and laws of the realm. 

Two observations of Saint Augustine would prove influential. In his treatise on the Freedom of the Will, he observed that “an unjust law would seem to be no law at all,” while in the Confessions he concluded that the “greater authority” of the divine and natural law is to be obeyed in priority to the “lesser authority” of human laws. Gratian, citing this latter passage in his systematizing commentary on canon law in the early twelfth century, drew the inference that legal customs and ordinances are to be held “null and void” if they are contrary to natural law.  

Building on these ideas, Saint Thomas Aquinas defined law as an ordinance of reason for the common good, made and promulgated by him who has care of the community. He proposed that four principal categories of law be recognized: the eternal law by which God governs the entire cosmos; the divine law, which is those aspects of the eternal law revealed in the Bible; the natural law, which is those aspects of the eternal law known by natural reason; and human laws, which are specific determinations of law applying the general principles of law to the conditions and circumstances of particular times and places. Like Augustine and Gratian, Aquinas considered that a human law that contains anything contrary to natural law has no binding force, that even a sound judgment issued without proper authority lacks justice, and that it is therefore expedient that the system of government should be organized and the powers of rulers tempered so as to avoid or prevent tyranny. 

Aquinas also recognized a distinction between the authority of the civil government and the authority of the Church, the former being responsible to make laws for the common good in temporal affairs, the latter responsible to make laws for the common good of the faithful in spiritual matters. This reflected a defining feature of medieval society, grounded in the teaching of Jesus Christ distinguishing between the things that belong to Caesar and the things that belong to God, and Saint Paul’s teaching that Christians are citizens of an alternative politeuma and ambassadors of the kingdom of heaven.  

Building on these ideas, in his masterwork De civitate Dei, St. Augustine proposed that there are two cities: the earthly city characterized by love of self, and the heavenly city characterized by love of God. Pope Gelasius I taught that, whereas the role of kings and the role of priests had once been combined (as when the Roman emperors bore the title pontifex maximus), after Christ the two roles were separated on account of “human weakness,” each operating in “its sphere of operation.” Consequently, there were “two swords” by which the world is ruled: the consecrated authority of the priests and the royal power. Especially after the investiture contest of the eleventh and twelfth centuries, the Roman concept of jurisdiction was used by civil lawyers and canon lawyers to identify the particular matters that fell within the authority of church and state. In the striking words of Étienne de Tournai: 

In the same city under the same king there are two people. With two people there are two types of life. With two types of life there are two forms of government. From the two forms of government arise two jurisdictions, the city and the church. The king of the city is Christ. There are two peoples and two orders in the church, clerics and laypeople. There are two types of life, the spiritual life and the life of the flesh. There are two types of government, priestly authority and princely power. There are two jurisdictions, divine and human justice, rights, and equity. If each is rendered its due, all things will be harmonious. 

This vision of paired authorities, each constrained within its proper sphere, did more than offer a tidy theological symmetry. It carried decisive consequences for how secular power itself would be conceived, limited, and made answerable to a higher law. The peculiar genius of medieval Europe was its refusal to vest all authority in a single source, and that refusal—worked out in canonist disputes, royal charters, and founding covenants—is what made constitutional government possible. 

Jurisdictional Boundaries and Higher Law 

According to Brian Tierney, it was the insistence on jurisdictional boundaries between popes and emperors, bishops and kings, priests and princes, that largely explains the emergence of what we know today as constitutional government. In Law and Revolution, Harold Berman has shown how the Western legal tradition came to be characterized by a plurality of jurisdictions and legal systems—not only ecclesiastical and imperial but also royal, urban, feudal, manorial, and mercantile. Berman argues that “this plurality of jurisdictions and legal systems” made “the supremacy of law both necessary and possible.” The result was a kind of “complex space”, as John Milbank has called it, in which a diversity of intermediate corporations and associations—religious, scholarly, commercial, and professional—operated within an overarching framework of law, qualifying the power claims of secular rulers and helping to keep them within constitutional bounds. 

Political authority was accordingly understood as a responsibility to administer justice according to law. John of Salisbury expressed a widely shared ideal when he said that the king should rule by law, according to justice, and with the counsel of the wise. Although the authority exercised by medieval kings was extensive, it was nonetheless considered to be subject to God and the law. Similarly, when Sir John Fortescue insisted in 1469 that English kings possess dominium politicum et regale (“political and regal lordship”) rather than dominium regale, he meant that they could rule only through laws to which the lords and commons had assented in Parliament. Otto von Gierke thus observed: 

The properly medieval … theory declared that every act of the Sovereign that broke the bounds drawn by natural law was formally null and void. As null and void therefore every judge … was to treat, not only every executive act, but every unlawful statute, even though it were published by Pope or Emperor. Furthermore, the unlawful order or unlawful act was null and void for the individual subjects of the State. It was just for this cause that their duty of obedience was conceived as a conditional duty, and that the right of actively resisting tyrannical measures was conceded to them. 

Bracton’s statement was cited by Chief Justice Coke in the case of Prohibitions del Roy to support the proposition that an English king cannot personally act as a judge but must allow the ordinary courts to fulfil that function in accordance with the law of the land. In Dr Bonham’s Case, Coke went further when he claimed that there had been many cases in which the common law had “controlled” Acts of Parliament and sometimes “judged them to be void,” particularly when it was found that they were “against Common right and reason, or repugnant, or impossible to be performed.” Most scholars have argued that Coke did not mean that the courts would regard unreasonable statutes as simply void, but rather that they would be interpreted in accordance with reason. However, some scholars, especially in the United States, have understood him to have been suggesting that unreasonable statutes would be declared entirely void and inoperative by the courts. Sir William Blackstone, another English lawyer who exercised significant influence in the United States, said: 

The law of nature, being coeval with mankind, and dictated by God himself, is of course superior in obligation to any other. It is binding over all the globe in all countries, and at all times; no human laws are of any validity, if contrary to this: and such of them as are valid derive all their force, and all their authority, mediately or immediately, from this original. 

By the nineteenth century, the rule of law had come to mean that the powers of government can be exercised only according to pre-existing law, and that all persons, no matter what their rank and status, are subject to the same set of legal rules and principles. As Albert Venn Dicey put it, “the rule of law is contrasted with every system of government based on the exercise by persons in authority of wide, arbitrary, or discretionary powers of constraint,” for it involves the principle that “every official, from the Prime Minister down to a constable or a collector of taxes, is under the same responsibility for every act done without legal justification as any other citizen.” 

The medieval and early modern traditions gave us a deeply considered account of the limits to which political authority is properly subject. What it had not yet given us was a written constitutional document, embodying those limits in textual form, and an institutional mechanism by which such a document might be enforced. Both of these were to be supplied—though not, as is often supposed, by the Enlightenment alone. The second part of this essay turns to the practice of writing constitutions, and to the Christian sources of the institution we now call judicial review. 

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