DE MONARCHIA OF DANTE ALIGHIERI
CHAPTER IV: The opponents' argument adduced from the sun and moon.
1. Those men to whom the entire subsequent discussion is directed assert that the authority of the Empire depends on the authority of the Church, just as the inferior artisan depends on the architect.  They are drawn to this by divers opposing arguments, some of which they take from Holy Scripture, and some from certain acts performed by the Chief Pontiff, and by the Emperor himself; and they endeavor to make their conviction reasonable.
2. For, first, they maintain that according to Genesis God made two mighty luminaries, a greater and a less, the former to hold supremacy by day and the latter by night.  These they interpret allegorically to be the two rulers  -- spiritual and temporal. Whence they argue that as the lesser luminary, the moon, has no light but that gained from the sun, so the temporal ruler has no authority but that gained from the spiritual ruler. 
3. Let it be noted for the refutation of this and their other arguments that, as the Philosopher holds in his writings on Sophistry, "the destruction of an argument is the exposure of error."  And because error can occur in both the matter and the form of an argument, a twofold fallacy is possible -- that arising from a false assumption, and that from a failure to syllogize. The two objections brought by the Philosopher against Parmenides and Melissus were: "They accept what is false, and syllogize incorrectly."  "False" I use here with large significance, embracing the improbable, which in matters of probability becomes the false element. He who would destroy a conclusion where there is error in the form of the argument must show a failure to comply with the rules of syllogizing. Where the error is material, he must show that an assumption has been made, either false in itself or false in relation to something else. Absolute falsity may be destroyed by destroying the assumption, relative falsity by distinction of meanings. 
4. Granting this, let us observe, in order to comprehend more clearly the fallacy of this and other arguments, that with regard to mystical interpretation a twofold error may arise, either by seeking one where it is not, or by explaining it other than it ought to be.
5. Of the first error Augustine says in The City of God: "Not all deeds recounted should be thought to have special significance, because for the sake of significant things insignificant details are interwoven. The plowshare by itself cuts the land into furrows, but that this may be accomplished the other parts of the plow are needed." 
6. Of the second error he speaks in his Christian Doctrine, saying that the man who attempts to find in the Scriptures other things than the writer's meaning "is deceived as one who abandons a certain road, only by a long detour to reach the goal whither the road led directly."  And he adds, "Such a man should be shown that a habit of leaving his path may lead him into cross-roads and tortuous ways." Then he gives the reason why this error should be avoided in the Scriptures, saying, "Shake the authority of the divine writings, and you shake all faith."  However, I believe that when such errors are due to ignorance they should be pardoned after correction has been carefully administered, just as he should be pardoned who is terrified at a supposed lion in the clouds. But when such errors are due to design, the erring one should be treated like tyrants who never apply public laws for the general welfare, but endeavor to turn them to individual profit.
7. O unparalleled crime, though committed but in dreams, of turning into evil the intention of the Eternal Spirit! Such a sin would not be against Moses, or David, or Job, or Matthew, or Paul, but against the Holy Spirit that speaketh in them. For although the writers of the divine word are many, the dictator of the word is one, even God, who has deigned to make known his purpose to us through divers pens.
8. From these prefatory remarks I proceed to refute the above assumption that the two luminaries of the world typify its two ruling powers. The whole force of their argument lies in the interpretation; but this we can prove indefensible in two ways. First, since these ruling powers are as it were accidents necessitated by man himself, God would seem to have used a distorted order in creating first accidents, and then the subject necessitating them. It is absurd to speak thus of God, but it is evident from the Word  that the two lights were created on the fourth day, and man on the sixth.
9. Secondly, the two ruling powers exist as the directors of men toward certain ends, as will be shown further on; but had man remained in the state of innocence in which God made him, he would have required no such direction. These ruling powers are therefore remedies against the infirmity of sin. Since on the fourth day man not only was not a sinner, but was not even existent, the creation of a remedy would have been purposeless, which is contrary to divine goodness. Foolish indeed would be the physician who should make ready a plaster for the future abscess of a man not yet born. Therefore it cannot be asserted that God made the two ruling powers on the fourth day; and consequently the meaning of Moses cannot have been what it is supposed to be. 
10. Also, in order to be tolerant, we may refute this fallacy by distinction. Refutation by distinction deals more gently with an adversary, for it shows him to be not absolutely wrong, as does refutation by destruction. I say, then, that although the moon may have abundant light only as she receives it from the sun, it does not follow on that account that the moon herself owes her existence to the sun. It must be recognized that the essence of the moon, her strength, and her function are not one and the same thing. Neither in her essence, her strength, nor her function taken absolutely, does the moon owe her existence to the sun, for her movement is impelled by her own motor and her influence by her own rays.  Besides, she has a certain light of her own, as is shown in eclipse. It is in order to fulfill her function better and more potently that she borrows from the sun abundance of light, and works thereby more efficaciously.
11. In like manner, I say, the temporal power receives from the spiritual neither its existence, nor its strength, which is its authority, nor even its function taken absolutely. But well for her does she receive therefrom, through the light of grace which the benediction of the Chief Pontiff sheds upon it, in heaven and on earth, strength to fulfill her function more perfectly.  So the argument was at fault in form, because the predicate of the conclusion is not a term of the major premise, as is evident. The syllogism runs thus: The moon receives light from the sun, which is the spiritual power; the temporal ruling power is the moon; therefore the temporal receives authority from the spiritual. They introduce "light" as the term of the major, but "authority" as predicate of the conclusion, which two things we have seen to be diverse in subject and significance.
1. Metaphys. 1. 1: "We reckon the chief artificers in each case to be entitled to more dignity, and to the reputation of superior knowledge, and to be more wise than the handicraftsmen, because the former are acquainted with the causes of things that are being constructed, whereas the latter produce things as certain inanimate things do, ... unconsciously." Bryce dates the successful claim of the papacy to rule in temporal matters to Gregory VII (1073-1086).
2. Gen. 1. 15, 16.
3. "Dua regimina" -- two guiding or governing powers. Bryce, Holy Roman Empire, c. 15: "The analogy between the lights of heaven and the potentates of earth is one which mediaeval writers are very fond of. It seems to have originated with Gregory VII" (1073- 1086).
"Two lights, the sun and the moon, illumine the globe; two powers, the papal and the royal, govern it; but as the moon receives her light from the more brilliant star, so kings reign by the chief of the Church who comes from God," are the words of Innocent IV (1243-1254).
Bryce speaks in the chapter cited above of a curious seal of the Emperor Otto IV (1208-1212), figured in J. M. Heineccius' De veteribus Germanorum atque aliarum nationum sigillis, on which the sun and moon are represented over the head of the Emperor: "There seems to be no reason why we should not take the device as typifying the accord of the spiritual and temporal powers which was brought about at the accession of Otto, the Guelfic leader, and the favored candidate of Pope Innocent III."
4. Dante's real view, that the spiritual and temporal rulers are coordinate but different, is expressed De Mon. 3. 16. 6. Again in Purg. 16. 106 is the idea in more figurative language: "Rome, that made the good world, was wont to have two suns, that showed the one and the other road, both of the world and of God. The one has put out the other, and the sword is joined with the crook; and the one and the other together of very necessity it behoves that they go ill."
Letter 6. 2 (To the Florentines) has the following figure: "Why, then, such a foolish supposition being disposed of, do ye, deserting legitimate government, seek new Babylonians to found new kingdoms, in order that the Florentine may be one policy and the Roman another? Why may it not please you to envy the apostolic monarchy likewise? that if Delia is to have a twin in heaven, the Delian One may also? "
After the death of Henry VII and Clement V Dante wrote in Letter 9. 10: "Rome, that city now deprived of both its luminaries."
5. Soph. Elenc. 18.
6. Phys. 1. 3. Parmenides was a Greek philosopher, born at Elea in Italy circ. 513 B.C., founder of the Eleatic School of philosophy, in which he was succeeded by Zeno. Melissus of Samos was one of his followers. These two false reasoners serve for illustration again in Par. 13. 122: "He returns not the same as he sets out, who fishes for the truth and has not the art; and of this are to the world open proofs Parmenides, Melissus, and Bryson."
7. "Distinction" marks out two possible meanings in a proposition; one, the sense in which it must be understood to make it true; the other, the sense in which it must be understood in order to support a given conclusion.
8. De Civit. Dei 16. 2.
9. De Doctr. Christ. 1. 36. Here Dante departs from our present reading of Augustine's text by using the words "per gyrum " instead of "per agrum."
10. L.c. 37.
11. "Litera," Witte says, was a solemn word used for "text," especially in referring to sacred writings, during the Middle Ages.
12. "Man restored to the state of Eden would not need ecclesiastical any more than he would need imperial guidance or authority. Hence Virgil 'crowns and mitres' Dante at the entrance of the Garden of Eden, Purg. 27, 42. It follows that Beatrice, whose ministrations begin here, may be Revelation, but cannot be Ecclesiastical Authority." Wicksteed.
13. The heaven of the moon was the first of the ten Dantean heavens. It is described Conv. 2. 3-7, and Par. 2-5. Nine of these were the so-called moving heavens, each having for its motor a certain order of spiritual creature. Conv. 2. 6. 5: "Wherefore it is reasonable to believe that the motive powers of the Heaven of the Moon are of the order of Angels."
Conv. 2. 6. 7: "These motive powers guide by their thought alone the revolutions over which each one presides."
14. De Mon. 3. 16. 9, and note.
The apostolic benediction even of Clement V, whom Dante punishes among the simoniacs in Inf. 19, is thus spoken of, Letter 5. 10: "This is he whom Peter, the vicar of God, admonishes us to honor; whom Clement, now the successor of Peter, illuminates with the light of the apostolic benediction, in order that where the spiritual ray does not suffice, the splendor of the lesser light may illumine."