It is fitting to add some representative texts of Saint Thomas Aquinas to the pontifical texts quoted in testimony of the Church’s social doctrine on the subject of Monarchical regimes given the prominence of his thinking in traditional Catholic teaching.
In De Regimine Principum, “having set forth these preliminary points,” it behooves men to live in society and therefore it is indispensable that a ruler govern them correctly, Saint Thomas goes on to say:
“We must now inquire what is better for a province or a city: whether to be ruled by one man or by many. Now this may be considered from the very purpose of government. For the aim of any ruler should be directed towards securing the welfare of whatever he undertakes to rule. The duty of the pilot, for instance, is to preserve his ship amidst the perils of the sea and to bring it to the port of safety.
“Now, the welfare and safety of a multitude formed into a society is the preservation of its unity, which is called peace, and which, if taken away, the benefit of social life is lost and moreover the multitude in its disagreement becomes a burden to itself.
“The chief concern of the ruler of a multitude, therefore, should be to procure the unity of peace: and it is not legitimate for him to deliberate whether he shall establish peace in the multitude subject to him, just as a physician does not deliberate whether he shall heal the sick man that is charged to him. For no one should deliberate about an end that he is obliged to seek, but only about the means to attain that end. Wherefore, the Apostle, having commended the unity of the faithful people, says: ‘Be ye careful to keep the unity of the spirit in the bond of peace’ (Eph. 4:3).
The more efficacious, therefore, a government is in keeping the unity of peace, the more useful it will be. For we call that more useful which leads the better to the end. Now, it is clear that what is one, can more efficaciously bring about unity than what is several; just as the most efficacious cause of heat is that which is by its nature hot. Therefore the rule of one man is more efficient than the rule of many.
“Furthermore, it is evident that several persons could by no means keep a multitude from harm if they totally disagreed, for a certain union is necessary among them if they are to rule at all. Several men, for instance, could not pull a ship in one direction unless joined together in some fashion. Now, several are said to be united to the extent that they act as one. So one man rules better than several who come near being one.
“Again, whatever is in accord with nature is best, for in all things nature does what is best. Now, every natural governance is governance by one. In the multitude of bodily members there is one that moves them all, namely, the heart; and among the powers of the soul one power presides as chief, namely, the reason. Even among the bees there is one queen and in the whole universe there is One God, Maker and Ruler of all things and this is reasonable. For every multitude is derived from unity. Wherefore, artificial things imitate natural things and since the work of art is better according as it attains a closer likeness to what is in nature, it necessarily follows that it is best, in the case of a human multitude, it is that one person rule it.
“This is also evident from experience; for provinces or cities which are not ruled by one person are torn with dissensions and are tossed about without peace so that the complaint seems to be fulfilled which the Lord uttered through the Prophet: ‘Many pastors have destroyed my vineyard’ (Jer. 12:10). But, on the contrary, provinces and cities, which are ruled under one king enjoy peace, flourish in justice and delight in prosperity. Hence, the Lord by His prophets promises to His people as a great reward that He will give them one head and that one Prince will be in the midst of them.”
The eminent Thomist, Fr. Victorino Rodriguez, O.P., adds the following comment to this explanation of the Angelic Doctor, which he enriches with other texts of Saint Thomas:
“On preferring monarchy to preserve the peace of society—It is undeniable that peace, in the positive, dynamic sense of ‘tranquil liberty’ (Cicero, II Philipp., chap. 13, 1), is the single most important factor for the common good, if not a synthesis of all its constituents and the aspiration of any honest government. Now then, insofar as peace partakes of order or unity, in and of itself it has a more direct and straight connection with a unitary or monarchic form of government than with other more pluralist or dispersed forms. This is one aspect of government that is stressed in these chapters; for intrinsic reasons of unity, through analogy with the natural order, from the lessons of history and because it is in accord with theocratic government. Later we will see also how a democratic government offers advantages for the peace of society.’
‘Now, the best government is government by one. The reason for this is that government is nothing but the directing of the things governed to their proper end, which consists in some good. But unity belongs to the idea of goodness, as Boethius proves (De consolatione, iii.) from this, that all things desire good, so do they desire unity; without which they would cease to exist.
For a thing exists in so far as it is one. Whence we observe that things resist division, as much as they can, and the dissolution of a thing arises from some defect therein. Therefore the intention of a ruler over a multitude is unity, or peace. Now the proper cause of unity is one. For it is clear that several cannot be the cause of unity or concord, except so far as they are united. Furthermore, what is one in itself is more apt and a better cause of unity than several things united. Therefore a multitude is better governed by one than by several.’”
Plinio Corrêa de Oliveira, Nobility and Analogous Traditional Elites in the Allocutions of Pius XII: A Theme Illuminating American Social History(York, Penn.: The American Society for the Defense of Tradition, Family, and Property, 1993), Appendix IV, pp. 397-399.