DE MONARCHIA OF DANTE ALIGHIERI
CHAPTER XV: In every sort of thing that is best which is most one.
1. Likewise I affirm that being and unity and goodness exist seriatim according to the fifth mode of priority.  Being is naturally antecedent to unity, and unity to goodness; that which has completest being has completest unity and completest goodness. And as far as anything is from completest being, just so far is it from unity and also from goodness. That in every class of objects the best is the most unified, the Philosopher maintains in his treatise on simple Being.  From this it would seem that unity is the root of goodness, and multiplicity is the root of evil. Wherefore Pythagoras in his Correlations  placed unity on the side of good and multiplicity on the side of evil, as appears in the first book on simple Being.  We can thus see that to sin is naught else than to despise unity, and to depart therefrom to multiplicity; which the Psalmist surely felt when he said, "By the fruit of their corn and wine and oil are they multiplied." 
2. Therefore it is established that every good thing is good because it subsists in unity. As concord is a good thing in itself, it must subsist in some unity as its proper root, and this proper root must appear if we consider the nature or meaning of concord. Now concord is the uniform movement of many wills; and unity of will, which we mean by uniform movement, is the root of concord, or rather concord itself. For just as we should call many clods concordant because all descend together toward the centre, and many flames concordant because they ascend together to the circumference, if they did this voluntarily, so we call many men concordant because they move together by their volition to one end formally present in their wills; while in the case of the clods is formally present the single attribute of gravity, and in the flames the single attribute of levity.  For power of willing is a certain potentiality, but the species of goodness which it apprehends is its form, which, like other forms, is a unity multiplied in itself according to the multiplicity of the receiving material, just as soul, number, and other forms subject to composition. 
3. These things being premised, we may argue as follows for the proposed exposition of the original assumption: All concord depends upon unity in wills; mankind at its best is a concord of a certain kind. For just as one man at his best in body and spirit is a concord of a certain kind,  and as a household, a city, and a kingdom is likewise a concord, so it is with mankind in its totality. Therefore the human race for its best disposition is dependent on unity in wills. But this state of concord is impossible unless one will dominates and guides all others into unity, for as the Philosopher teaches in the last book to Nicomachus, mortal wills need directing because of the alluring delights of youth.  Nor is this directing will a possibility unless there is one common Prince whose will may dominate and guide the wills of all others.  If the conclusions above are true, as they are, Monarchy is essential for the best disposition of mankind; and therefore for the well-being of the world Monarchy should exist therein.
1. "Priority" translates the Latin word prius. See Arist. Categ. 12. Moore. Conv. 3. 2. 2: "The first of all things is being, and before it is nothing."
2. Metaphys. 1. 5.
3. The central thought in the Pythagorean philosophy is number, it being the principle and essence of everything. The theory of opposites gave rise to the Pythagorean , parallel tables, or correlations: --
See the article on Pythagoras in Toynbee, Studies, pp. 87-96. Conv. 3. 11. 2: "In the time of Numa Pompilius ... there lived a most noble philosopher, called Pythagoras."
4. Metaphys. as in note 2. Cf. Conv. 2. 14. 10: "Pythagoras ... puts odd and even as the principles of natural things, considering all things as number."
The unity of goodness is one of the cardinal points in Dante's philosophy. It is his theory of form and his theory of justice. So the poet of the Divine Comedy makes God in the Empyrean visualized unity, as Satan in Hell is visualized multiplicity. Par. 28. 16: "I saw a point which radiated light so keen that the sight which it fires must needs close itself: ... From that point depends the heaven and all nature."
Par. 33. 85: "I saw how there enters, bound with love in one volume, that which is distributed through the universe; substance and accident and their fashion, as though fused together in such wise that that which I tell of is one single light. The universal form of this knot I believe I saw." See Inf. 34. 37 for the description of Satan.
5. Ps. 4. 7.
6. Eth. 2. 1. 2: "The stone which by nature goes downward could never be accustomed to go upward, ... nor could fire be accustomed to burn downward."
Conv. 3. 3. 1: "Everything ... has its special love; as simple bodies have a natural love for their own place; wherefore earth always falls toward the centre, and fire is drawn toward the circumference above."
Inf. 32. 73: "We were going toward the centre, to which all gravity is collected." L.c. 34. 110: "The point to the which from every part the weights are drawn."
Purg. 18. 28: "As the fire moves on high, by reason of its form, so ... the mind seized enters into desire, which is a motion of the spirit." Also Purg. 32. 109.
Par. 1. 115: "This bears away the fire toward the moon; this is the motive power in the hearts of men; this binds the earth together and makes it one." Cf. Par. 1. 133, 141 ; 4. 77; 23. 42.
7. The species of good which anything apprehends is its form, that principle which makes it what it is. In this case the volitional power of willing is the material or matter, while the species or sort of goodness which is the end of the volition is the form. So it makes no difference how many people will, so long as they will the same thing, for the form is then the same, if the material is various.
The composite character of the soul is treated Conv. 3. 2. 3, where it is shown to have three powers, vegetable, sensitive, and rational according to Arist. De Caelo 2. See Purg. 25. 74.
8. Conv. 3. 8. 1: "Of all the works of Divine wisdom, man is the most wonderful, considering how Divine power has united three natures under one form, and how subtly harmonized must his body be with that form."
Conv. 3. 15. 5: "The beauty of the body results from the proper ordering of its members."
Conv. 4. 25. 7: "The proper ordering of our members produces a pleasure of I know not what wonderful harmony."
9. Eth. 10. 9. 8: "To live temperately and patiently is not pleasant to the majority, and especially to the young."
10. Conv. 4. 9. 3: "We may almost say of the Emperor, wishing to represent his office by a figure, that he is the rider of human will. And it is very evident how wildly this horse goes over the field without a rider."