The Rule of Law and the Rule of Reason

Steven Grosby’s essay is an excellent contribution on the formal and procedural elements that must be upheld to maintain the rule of law. Grosby’s essay, however, invites us to unpack what kind of “reason” is inherent in law and to ask what it means for law “to rule.” The 13th century theologian and philosopher Thomas Aquinas did not treat “rule of law” with the sophistication that we expect from jurisprudents today.  But he had a remarkably deep and clear understanding of the underlying philosophical question: Does law belong chiefly to reason, or does it pertain chiefly to the force of will?

Thomas’s contribution to the idea of the rule of law occurred during a period that witnessed profound and far-reaching cultural change with respect to the function of law and force in human social orders. Peter Abelard’s autobiography, written about 1132, furnishes us a “snapshot” of this change afoot in western Europe. At the outset, Abelard writes:

For my part, the more I went forward in the study of letters, . . . the greater became the ardour of my devotion to them, until in truth I was so enthralled by my passion for learning that, gladly leaving to my brothers the pomp of military glory, I fled utterly from the court of Mars that I might win learning in the bosom of Minerva. (Historia Calamitatum).

Fleeing the court of Mars for the bosom of Minerva, Abelard personally typifies a European renovatio, or renaissance, that began in the 12th century, and increased in tempo and scope until the time of the Great Plague of the 14th century.

At the time of Abelard’s birth 1079, we must imagine a western European culture bound not by law, but rather by feudal oaths and the chivalric code. They fought over vineyards, over the control of rivers, roads, treasuries, over far-flung family dynasties – but, above all, they fought for the sake of honor.  At the beginning of the 12th century, no realm of western Europe had an organized legal system. Criminal procedures in some cases relied upon the so-called trial of ordeal – by combat, by fire, or by water. The Court of Mars, in fact, was not a “court” in any sense that we would recognize. One procured the ad hoc judgment of a lord, and then sent one’s family and vassals to execute the judgment. Indeed, it was a decentralized system of private law and vindication.

As universities sprouted up like mushrooms, the faculties of law were the prototype of other faculties. We often think of the medieval university in terms of philosophy, theology, and medicine.  But the lawyers were there first on the scene. It makes sense. What is the opposite of the Court of Mars but the Cult of Law?  What did the masters and students find when they studied the newly recovered books of Roman law?[1]  In the first paragraph of the Digest they read the boast of the jurist Ulpianus: “those who profess the law are priests” (Dig. I, I, 1).  Priests of what? Cultus pacis, cultus iustitiae – the cult of peace and justice. They also contemplated the first sentence of Justinian’s Institutes: “The imperial majesty must be not only distinguished in arms but also armed with laws.” Thomas Aquinas himself would borrow that phrase, describing human law as the arma rationis, the arms or tools of reason. (S.t. I-II, 95.1).

Until the 12th century, there was no free-standing discipline of law. Law was a branch of rhetoric, leading to a practical career in writing and notarizing official documents. Lawyers were little more than scribes.  But when the scientific study of law emerged at Pavia and Bologna, it would have remarkable and almost immediate results. In 1139, Gratian produced the Decretum, the first systematic exposition of canon law. It became the template for the scholastic method in theology and philosophy. Civilian legal scholars did the same for the Roman law, accumulating and organizing as many as 100,000 different glosses on the Digest and other books of the law. In both systems, the dicta of authorities were transformed into a coherent whole; decretals and responses to individual cases were organized into a system of precedents; legal procedures replaced trials by ordeal – indeed, in 1215, Pope Innocent III forbade clerics from taking part in such trials.  Popes and Emperors had their own legal opinions collected into books and published into order to facilitate their study by legal professionals.

Above all, Europeans discovered the art of legislation. The Nobel Prize winning economist, Friedrich Hayek wrote:  “[T]he deliberate making of law, has justly been described as among all inventions of man the one fraught with the gravest consequences, more far-reaching in its effects even than fire and gun-powder.”[2]  We can roughly mark the date when this new kind of gunpowder was invented.  The year was 1231.  Thomas Aquinas was only six years old.  The Holy Roman Emperor, Frederick II, who was also King of Sicily, sat down and wrote a constitution.  It was called the Liber Augustalis, or more commonly the Constitutions of Melfi.  The Emperor ordered his scholars to survey the feudal customs and common law of his kingdom.  He then proceeded to transform it into royal law. If customs needed to be changed, he changed them; if laws were missing, he simply created them; he outlawed private vendettas; he provided for civil and criminal procedures.  Here was a new kind of sovereign who did something more than exercise judgment in cases and controversies.  He wrote the law.

When Thomas, in the mid-13th century, wrote his 18 questions on law in the Summa theologiae, he inherited a world that was shaking off its feudal customs.  Along with the renovatio of legal studies and practices, there emerged a new confidence and interest in the “political” dimension of human affairs.  Thomas’s Treatise on Law consists of 18 questions and 96 articles (S.t. I-II, 90-108).  I shall consider two issues that arise in the very first article of the first question of the treatise.  Here, we can see how Thomas appropriates and contributes to this new cultus pacis, cultus iustitiate.  The moment is so quiet that we are apt to pass over it without noticing the ambient noise of the original setting.


In question 90, Thomas sets out in four articles to gather an essential definition of law.  Law, he writes, is an ordinance of reason, for the common good, made by a competent authority, and promulgated.  We should note that coercion, or what was called the vis coactiva, is not included among the four essential traits of law.  In the very first article, Thomas asks “whether law pertains to reason.”  He answers that law directs human acts by way of a moral rather than a physical necessity; that is to say, law moves rational agents to an end not by force but by obligation.  Lex is derived from the verb ligare – to bind.  However, this is not to be understood in a physical sense of a superior motion necessitating a motion in another body.  This kind of necessity, as the ancient jurists said, “knows no law.”  For example, a legislator might try to post a law that no one shall get sick on a boat, or digest their food, but everyone understands that such events are not bound by law in the proper sense of the term.  To be sure, we read two questions later (92.1) that coercion is an act of law – it is the instrument, as it were, of the law, but it is not the law itself.  Without the law, coercion is violence.

The idea that law is essentially a precept, a binding directive communicated by one mind to others was implicit in the legal renaissance of the 12th and 13th centuries. Indeed, it summarizes the new humanism under the auspices of Minerva rather than Mars.  But . . . it met with serious resistance from two parties.

The first was the Augustinian party.  For centuries, monks, theologians, and princes had read the scriptures.  Not only in Jewish scripture, but in the New Testament itself, there seemed to be ample evidence that, in the order of divine providence, law has principally a corrective and penal function. In Paul’s Letter to the Romans, for example, we read that “law works wrath” and “where there is no law there is no transgression” (Rom. 4:15).  No less an authority than St. Augustine forcefully contended that temporal law exists only for one class of men:  the “unhappy class,” namely those men who are not properly subordinated to the eternal law, and who therefore need an imposed law.  Such law is just, as a punishment for sin. Human law would not have existed without the fall of our first parents.  Indeed, imposed law is a constant reminder of our loss of dignity, while the absence of imposed law is the sign of the recovery of that dignity under the sway of charity.

Against this wrath-model of law, Thomas offered a counter-factual hypothesis.  Suppose that the original state of innocence was never ruptured.  Would there have been need for one man to command another?  He concedes right away that there would have been no need for the corrective or penal function of authority.  But there would have been need for directive authority.  He writes:  “First, because man is naturally a social being, and so in the state of innocence he would have led a social life. Now a social life cannot exist among a number of people unless under the presidency of one to look after the common good; for many, as such, seek many things, whereas one attends only to one. Wherefore the Philosopher says, in the beginning of the Politics, that wherever many things are directed to one, we shall always find one at the head directing them.” (S.t. I, 96.4).

Wherever a plurality of rational agents seek through their united action a common good, and whenever there is a plurality of valid means for achieving the end, there will be need for binding directives, obligating the group to follow this means rather than another one. This level of governance is not to be confused with the removal of a deficiency, for there is no issue of anyone selecting morally wicked means to an end. The directive or coordinative function of law would have been necessary even without sin. And therefore the corrective or penal function of law is accidental – to be sure, it is a very important “accident,” and for all practical purposes, no ruling authority could hope to preserve the common good by ignoring it. Even so, it should not be confused with the essence of law.

Augustine was correct, but he didn’t answer the right question. Thomas’s question, which represents the new humanism of the legal renovatio, is not whether law is entitled to coerce and punish, but whether we can discern a more purely political office of law. The counter-factual scenario of a state of nature as yet untrammeled by sin and injustice is meant to turn our attention to what law does every day: namely, to coordinate the actions of the good and the bad alike to a common good.  Delicately but decisively Thomas turns upside-down the older notion of law as the expression of wrath and the projection of force. He doesn’t deny the role of wrath, but simply removes it from the foundation of law.

The second source of resistance came, interestingly, from the Roman civil tradition being recovered in the schools and courts of Europe.  Both the papal and the imperial legal traditions were preoccupied with the legitimacy of their titles to rule. One of those titles was the imperial ideal itself.  The Roman legal tradition, first codified by Justinian, was deeply tinctured with the premises of imperial absolutism. Justinian himself asserted: “God had sent among men the emperor as a ‘living statute’, to whom statutes themselves were subject” (Nov. 105, 2, 4). There was the famous dictum that the ruler’s will has the force of law (quod voluntas principis habet vigorem legis) (Dig. I, 4, 1; S.t. I-II, 90.1 ad 3). And, finally, the most blunt instrument in the toolkit of imperial power, princeps legibus solutus est – the ruler is not bound by the laws. This notion of a unilateral kingly power, exempt from its own laws, was a problem distinct from, but nevertheless intertwined with, the problem I discussed earlier under the rubric of Augustinianism.

According to a venerable tradition, it was held that human law is made chiefly, if not solely, for the correction of bad men. This explains why, for most of the middle ages, the mark of aristocracy was immunity from human law.  The idea of immunities as the privilege of aristocracy emerged from two traditions. First, from the notion that law is made for bad men, and thus good men ought to enjoy immunities.  Second, from the echoing effect of the ancient imperial ideal princeps legibus solutus est – the ruler is not bound by the laws.  Aristocracy therefore participate in the kingly power by having its own piece of his immunity. These immunities included everything from taxation to uses of lethal force. Not only was there a bewildering array of different jurisdictions, but within and across jurisdictions there were immunities.


Thomas saw the nature of the problem. Frankly, he did not contribute any practical or institutional solution to it. But he did try to philosophically clarify the issues.  Let’s return to where we began, with the first question of his Treatise on Law. Here, Thomas insists that law is a work of reason. For it is reason that apprehends a proportion between an act and its end.  Before there can be a force of law (vis legis) there must be a ratio legis. Therefore, command is chiefly a work of reason.  Executive force without the reason of the law is just that, force.  Without reason, there is nothing for the will to execute.

[I]t should be said that reason has its power of moving from the will, as stated above [q. 17.1], for it is due to the fact that one wills the end that the reason issues its commands as regards things ordered to the end.  But in order that the volition of what is commanded may have the nature of law, it needs to be in accord with some rule of reason.[3] And in this sense is to be understood the saying that the will of the sovereign has the force of law. Otherwise, the sovereign’s will would savor of injustice [iniquitas] rather than of law.  90.1 ad 3.

At issue is not whether the ruler of a political community should rule by law, but whether the rule of law proceeds from executive power. And this in turn depends on how we understand the relationship between the intellect and the will. No one, of course, would deny that the ruler ought to govern intelligently. The question, rather, was whether the intellect is but an instrument of the will willing. Or, to put it in another way: Is law superior force conjoined with instrumental rationality?

Consider what is at stake for the legal renaissance of that era. What’s the point of the new scientific study and organization of the law? What do we mean when we say that law should rule? On a voluntarist model, all of this work is ordered to the acquisition of the titles and instrumental resources put at the disposal of superior force.  In other words, law is studied in terms of the technical armature facilitating the will of the sovereign. On an intellectualist model, such as what Thomas defends, study of the rationes legis (reasons of the law) is organically related to the intellect’s governing what ought to be willed. Command, Thomas contends, is chiefly an act of the intellect (S.t. I-II, 17.1).

To the much vexed question of whether the ruler is immune from his own laws, Thomas faced a deeply entrenched tradition – even has he wrote these questions on law, spiritual Franciscans, relying upon the eschatological prophesies of Joachim de Fiore, claimed to be solely under the guidance of the Holy Spirit. This expression of antinomianism had remarkable affinity to the imperial notion that the Emperor is a “living statute.”

In typical scholastic fashion, Thomas tackles the problem by making a threefold distinction (S.t. I-II, 96.5).

In the first place, law contains two things. On the one hand, its essential property, namely, to be a rule of human acts toward a common good. Second, its use of coercion for the disobedient.  Therefore, any agent (not just the ruler) can be said to be either above or subject to law in two quite different ways. Those who are good are subject not to law’s coercive power but only, or for the most part, to its essential, directive function.  Indeed, the virtuous are more rather than less subject to law’s directive purpose.

In the second place, someone may be exempt from a law because the ruler does not have jurisdiction over the matter. So, for example, the natural law requires both rectitude in the external act and rectitude in the internal act of the will (S.t. I-II, 91.4). Human authorities, however, have no immediate jurisdiction over the actus interior. Moreover, someone might enjoy exemption from a particular command because the ruler has no jurisdiction over the exterior act. For example, the king has no power over the sacramental order. But in neither of these cases is one exempt from law – for such commands lacking proper jurisdiction are not laws at all.

In the third place, the ruler is exempt from law in at least three senses. Here, I quote from Thomas.

[I]t should be said the sovereign is said to be exempt from the law as to its coercive power, since, properly speaking, no man is coerced by himself, and law has no coercive power save from the authority of the sovereign.  Thus is the sovereign said to be exempt from the law, because none is competent to pass sentence on him if he acts against the law.  Hence, on the text of the Ps. 50  [“To Thee only have I sinned”],[4] a gloss says that “there is no man who can judge the deeds of a king.”[5]  But as to the directive force of law, the sovereign is subject to the law by his own will; according to the Decretals: “whatever law a man makes for another, he should keep himself.”[6]  And a wise authority says: “Obey the law that thou makest thyself.”[7] Moreover, the Lord reproaches those who “say and do not,” and who “bind heavy burdens and lay them on men’s shoulders, but with a finger of their own they will not move them,” as had in Mt. 23.[8]  Hence, in the judgment of God the sovereign is not exempt from the law as to its directive force, yet he should fulfill it of his own free-will and not of constraint. Yet the sovereign is above the law, insofar as, when it is expedient, he can change the law and dispense it according to time and place.

To summarize.

  • The ruler is exempt from the law as to its coercion. He cannot coerce himself. But this leaves entirely intact the primary predicate of law, regarding which the ruler is not exempted.
  • In another way, a ruler can be exempt from the law insofar as he is supreme, which is to say, he is the final arbiter. This, however, does not entitle the ruler, in his adjudicative function, from being directed by the law applying to the facts of the case.
  • Finally, a ruler can be exempt from laws insofar as he has the office of amending or changing laws. This, however, does not imply an exemption from law as such, including the general standing laws of the kingdom he might amend.

Above all, Thomas was concerned that the dictum princeps legibus solutus est was incompatible with the broader context and indeed the telos of the rule of law.  Namely, the natural ordination to political community. Whereas a parent is exempt from his commands to a child, political community entails a certain reciprocity that is destroyed by despotism.  In his Commentary on the Politics, he writes:

Now the city is governed by a twofold rule, one political and the other regal.  Regal rule obtains when the one who presides over the city has full power; political rule, when his power is limited by civil laws. . . . I Pol., lect. 1 (#13)

For Thomas, regal rule is a species of despotism.  Here, we should recall the difference between despotism and tyranny. The tyrant orders the common good to his own private good.  The despot, however, orders things to a common good, but in such a way that the things ordered cannot resist or talk back.

Political community, on the other hand, requires the unity of parts, which have their own proper operations and activities.  Each person senses, thinks, wills, and pursues the life of a farmer, a soldier, a monk or a merchant. The “parts” of this kind of unity can “talk back,” as it were.  Reciprocity is an essential characteristic of the political. Therefore, the dictum princeps legibus solutus est needed to qualified.

First, because it would put the ruler outside of the political community; he would stand to the political society as soul stands to the body, or as parent to child. This would spell the death of political friendship.

Second, because a unilateral projection of power is inconsistent with civic virtue.

For Thomas, as for Aristotle, civic virtue is not mere passivity in receiving commands. “Rulers imposing a law,” he writes, “are in civic matters as architects regarding things to be built,” whereas civic prudence is concerned “with individual operable things.” As legislative prudence “gives the precept,” so also “civic prudence puts it in effect and conserves the norms stated in the law.”[9] Notice that the civic virtue governs the action where by those who receive a law conserve and effect it.  Citizens therefore are not only directed but also direct themselves. The ruler who presides exercises legislative prudence, but he is also bound to exercise civic prudence insofar as he is directed by the laws he makes. To stand outside of this circle is to stand outside the rule of law.


I have tried to throw light on one question: whether law is force. As I said earlier, I have aimed to put the ambient noise back into that question. Permit me to conclude by returning to that comment by Friedrich Hayek: “[T]he deliberate making of law, has justly been described as among all inventions of man the one fraught with the gravest consequences, more far-reaching that in its effects even than fire and gun-powder.”  Thomas lived just at the moment when ruling authorities – civil and ecclesiastical – began to flex their legislative muscles.  Make no mistake.  Thomas supported this project.  Scandalously, perhaps, he devotes only one article in the entire Treatise on Law to the issue of custom. The default position, for Thomas, is that of customs being converted into legal precedents, and precedents organized within a legal system, and a legal system marked by legislation.

But it was also part and parcel of the rebirth of the political. Remarkably, the natural virtue that he puts on par with charity is legal justice:

for just as charity may be called a general virtue in so far as it directs the acts of all the virtues to the Divine good, so too is legal justice, in so far as it directs the acts of all the virtues to the common good. Accordingly, just as charity which regards the Divine good as its proper object, is a special virtue in respect of its essence, so too legal justice is a special virtue in respect of its essence, in so far as it regards the common good as its proper object. And thus it is in the sovereign principally and by way of a mastercraft, while it is secondarily and administratively in his subjects.  II-II, 58.6

The superiority of the political community requires a proper estimation of this new legal prowess – ius facere, or legislation. Much depends on whether law is merely a new-fangled technique of kingly force, or whether it is deployed within a system that is properly political. I have always been uncomfortable with the idea, propounded by Lord Acton, that Thomas was the “first Whig” because he defended liberty and just revolution.[10] There is some truth to what Acton said. But Thomas did not side with either the party of liberty or the party of authority. In his own time and place, these two parties reserved to themselves exemptions from law. For Thomas, this implied exemption from political order.  And that would mean, at least in this life, exemption from the form of order naturally suited to reconcile liberty and authority. The Christian middle ages did not decisively resolve this question; in fact, Thomas’s questions of law would not have a significant impact on political debate for another three centuries – during the Age of Absolutism. From that perspective, when Hobbes became the opponent of Bellarmine and the Baroque-era Thomists, Aquinas does begin to look like the Whig. But that is a story for another time.

[1] On these aspects of the legal renaissance, see: Stephan Kuttner, “The Revival of Jurisprudence,” and Robert L. Benson, “Political Revovatio: “Two Models from Roman Antiquity,” in Renaissance and Revewal in the Twelfth Century, eds. Robert L. Benson and Giles Constable with Carol D. Lanham (Cambridge: Harvard University Press, 1982), at 299-323 and 339-386.

[2] F.A. Hayek, Law, Legislation, Liberty  (1973) at 72.

[3] Thomas uses the term ratio legis (reason or nature of law).  An ordinance is said to have vis legis (force of law) not simply by dint of volition, but insofar as it is based on, or expresses, a rule of reason. However, Thomas is not suggesting that any rule of reason is a law. For a rule of reason to count as lex, other conditions must be met.  See infra q. 90.2, 3 ad 3.

[4]Ps. 50.6

[5]Glossa Lomb. (PL 191, 486).

[6]Decretals, Greg. IX,  Lib. I, tit. 2, cap. 6 (RF II, 8). See Monahan (1987).

[7]Decius Ausonius, Sept. Sap. Sent., vers. 5 (PL 19, 876).

[8]Mt. 23.3-4.

[9] Thomas, In Eth., lectio 9 (1197).

[10] Selected Writings of Lord Acton, vol. III, ed. J. Rufus Fears (Indianapolis: Liberty Classics, 1988), 536; and Vol. I, at 34.