An important part of any political philosophy seems to be the question of Constitution. Plato and Aristotle both spend time in their seminal works on politics to understand the forms of government. For Plato those regimes are Aristocracy, Timocracy, Oligarchy, Democracy and Tyranny. Aristotle expands on those regimes by excluding Timocracy and adding Kingship, and Polity. The Neo Platonic and Aristotelian thinkers of the Middle Ages took a similar view on the forms of government. St. Thomas Aquinas is no different than his fellow Middle Age thinkers and devotes time to understanding the various forms of government. In the First Part of the Second Part of his Summa Theologiae Aquinas lays out his Treatise on Law. Within that treatise, in question 95 article 4, Aquinas argues for five forms of government. Within his discussion of the forms of government a series of important questions are brought forth including, the relationship between law and regime, the place of the ecclesiastical within the civil society, and what can be determined as Aquinas’ best regime despite what he explicitly states.
First it is necessary to examine the regimes laid out by Aquinas and also their corresponding form of law. By understanding the type of law associated with each regime and what Aquinas believes to be the best regime as a result we may gain a better understanding of their relationship. From there it seems proper to discuss the place of the ecclesiastical authority within the civil society and in particular whether or not Aquinas gives any authority to the ecclesiastical. Finally, based on his three statements found in questions 95, 105 of the Summa and On Kingship we may come to some understanding of what Aquinas understands as the best regime.
Aquinas explicitly discusses his regimes and their relationship to human law in question 95 article 4. The first regime Aquinas mentions is monarchy, and the form of law associated with this regime are “royal ordinances.” Aristocracy is the second regime and is associated with “authoritative legal opinions and senatorial decrees.” Oligarchy is associated with “praetorian law” or what Aquinas also calls, “honorary.” Democracy is the final regime associated with law, as tyranny is lawless, and democracy has, “acts of plebian assemblies.” It is curious that Aquinas does not place the distinction of human law in particular on any of the regimes. The closest are Aristocracy and Oligarchy yet even those are only “opinions” and “honorary” laws. And considering the regimes and the form of law associated with them, Aquinas declares that none are the best government. This is unique given that in question 105, and in his work On Kingship where Aquinas declares that Kingship is the best form of government. Yet in light of the relationship between regime and law none seem to have authoritative human law associated with them. This may be because Aquinas states that the best is a mixed regime with Kingship, Aristocracy and Democracy. However, if, none of the political regimes have law proper, then where does one receive law? Can authoritative human law be achieved through the temporal, or must one look towards someplace else? Aquinas exhibits four kinds of law: Eternal, Natural, Divine and Human law. The Human law is a reflection of the Natural and Divine laws. The Natural law is the Eternal Law’s participation in human reason. Therefore, it would appear as though only the ecclesiastical can make authoritative human law.
While Aquinas does not, in these sections, directly reference the relationship between the temporal and the ecclesiastical. However, using what Aquinas states in questions 95 and 105 of the Summa and On Kingship it nonetheless appears important to discuss that relationship. The polity is declared in question 95 to be the best regime. In question 95 of the Summa, polity, a mix of Kingship, Aristocracy and Democracy, is declared the best regime; this polity could be likened to the regime found in England. However, does Aquinas mean by polity a mix of temporal and ecclesiastical authority with the Papacy at its head as king, and local aristocratic and democratic assemblies to deal with the day to day operations of the civil society? At the time the Papacy was only beginning to take the traditional title of Kings, “Vicar of Christ” for itself. However, based on Aquinas’ view of the Human law, it would appear that the ecclesiastical authority is necessary in the creation of human law. And so looking at this possible relationship between the two spheres, temporal and ecclesiastical, then one may see in Aquinas his willingness to give to the Papacy political authority in connection with the Papacy’s emerging claim to the title of Vicar of Christ. Authoritative Human law could be possible under Papal rule, if one assumes that Human law is a reflection of the Natural and Divine laws and that they can only be decreed by members of the clergy. If this in fact is true, then a starker contrast can be seen between Aquinas and the moderns, even a starker contrast between Aquinas and a fellow medieval like Dante. The alternative to seeing Kingship as filled by a temporal, civil leader rather than by the Papacy would call into question Aquinas’ belief that the ecclesiastical has any authority within civil society at all.
And so having examined what Aquinas defines as the political regimes, and what he explicitly states as the best regime and the place of the ecclesiastical within civil society we can now turn our attention to be better understand what exactly Aquinas’ view of the best regime is. Within the Treatise on Law and On Kingship Aquinas states his view on the best regime three times. In question 95-4 the best regime, as already stated, is a polity with Kingship, Aristocracy and Democracy. Yet ten questions later Aquinas contradicts himself by stating the best regime is Kingship. And then again in On Kingship the best regime is seen as Kingship. Looking at On Kingship we may dismiss the account of the best regime on one major premise, the treatise is written to the King of Cyprus. The seriousness of Aquinas’ claim in On Kingship, therefore, can only be taken in light of question 105-1 from the Treatise on Law. Yet, an understanding here may be taken in light of question 95-4 where he indicates polity will include kingship. However, in his On Kingship Aquinas states, “Man therefore needs something to guide him towards his end.” This guide is a ruler, whether it is a King, aristocrat, oligarch, or democrat and the end appears to be, “man may devote his reason to some particular branch of learning.” The best guide or form of government, in On Kingship is Kingship. He further defends his argument for Kingship as the best regime on the grounds that government of many is more likely to become unjust than the government by one. The question of government by many is explained by Aquinas as, “For there is no beauty in a body unless all its members are properly disposed, and ugliness arises when even one member is improperly so” In each instance throughout On Kingship Aquinas appeals to what might be called the energy and efficiency of the one over the many. In addition, Aquinas considers that if there are three rulers and one is corrupt than the whole is corrupt. Both of these reasons are why Aquinas suggests that Kingship is the best possible regime.
However, in his Treatise on Law it appears that the best government, polity, corresponds to that government with the most authoritative law. Throughout the whole of the Treatise on Law it appears that law is the ultimate good given to man by God as it allows man to know and participate in the Divine As such, it appears that the best regime must have the best human law associated with it. As Aquinas says in questions 90 and 92 in his Treatise on law, “A law, properly speaking, regards first and foremost the order to the common good,” indicating that the best regime should be the one that best orders the common good. He goes on to say, “Consequently it is evident that the proper effect of law is to lead its subjects to their proper virtue: and since virtue is “that which makes its subject good,” it follows that the proper effect of law is to make those to whom it is given, good, either simply or in some particular respect.” And as before, it would appear that the best regime would be the one that best makes its subject good. And since Aquinas argues that the best regime in relation to law is polity, it would follow that the best regime simply for Aquinas would be polity.
Therefore, in looking at his description in the Treatise on Law and On Kingship of the best regime, the argument from the Treatise on Law that the best regime is the one with the best law seems to be stronger than the one in On Kingship. Because the argument in the Treatise on Law appears stronger, we may assume that Aquinas believes polity is the best government albeit with the proper form of kingship. This appears true because the role of law is so important in human affairs for Aquinas throughout the Treatise on Law.
Aquinas’ description of the regimes calls into question three key things, the relationship between regimes and law, the role of the ecclesiastical in civil society, and what appears to be Aquinas’ view of the best regime based on the relationship of regimes and law. Some may question the necessity of addressing the role of the ecclesiastical in society because Aquinas himself does not address this. However, because of the historic role of the Church at the time of Aquinas and the centuries immediately following his life one cannot exclude the possible implications of ecclesiastical in society. And because Aquinas states in various locations differing views of what can be called the best regime it is necessary to attempt to better understand Aquinas’ view based on what he says but not necessarily what he says is the best regime; i.e. the role of the regime in human life, and the role of law.
 Plato’s Republic book VIII. Plato also states that Aristocracy degrades into Timocracy, which degrades into Oligarchy and then into Democracy and finally into Tyranny.
 Aristotles’s Politics book III and IV. Aristotle claims that Kingship is the most desired regime and this differs from Aquinas’s view in On Kingship where he calls it the best regime. Aristotle calls polity the best possible regime and it is here in Question 95 of the Treatise on Law that Aquinas agrees with Aristotle’s account.
 Aquinas, Thomas. Summa Theologiae IaIIae 95-4 in Aquinas: Political Writings edited by R.W. Dyson, (New York, Cambridge University Press, 2008) pg. 135
 Summa Theologiae I, II, 95-4 pg. 136
 “A kingdom is the best form of government of the people” Summa Theologiae I, II, 105-1. And, “The rule of the King is best.” On Kingship, pg. 11. One must call into question Aquinas’s declaration of kingship in On Kingship as it is a letter written to the King of Cyprus. As such, one may argue that Aquinas is simply appeasing the king in declaring kingship to be the best regime. His seemingly contradictory statements in the Treatise on Law may be rectified by demonstrating that Kingship is one of the regimes in the Polity and that Polity should be in the form of a kingship, albeit with Aristocracy and Democracy elements.
 Aquinas Political Writings, pg. 5
 Aquinas Political Writings, pg. 17, “If, however, one man rules…” and “For when dissension arises.”
 Aquinas Political Writings, pg. 13.
 Summa Theologiae, 1.1.90-3
 Summa Theologiae 1.1.92-1