Tetrabiblos (The Quadripartite Book)

Hieronymus Salius Faventinus, Doctor of Arts and Medicine, to Domenico Maria Novara of Ferrara, Doctor of Arts and Medicine and most excellent astronomer: Greetings regarding the nobility of astrology.

There are many who are insolent and slanderous, and to many, most dear Domenico, they are sluggish; they consider this part of our astronomy, which we call judicial, to be of little account and entirely to be despised, and they proclaim this daily. These men, indeed, because of the dullness of their intellects and, so to speak, the gross thickness of their minds, cannot reach even the smallest part of it. Others, who say they see many judgments of judicial astronomy to be void, vain, and without truth, boldly and rashly presume to pronounce this part of astronomy of which we speak, I know not [what to call it], but to label it as fables and deception. We, however, leaving the sluggish with their sluggishness and the slanderers with their slander, prove that this part of our astronomy is to be numbered among the speculative sciences. For it will easily be made clear that it should be called a science if we make known what a science is and how it is acquired. For what else is a science than a habit acquired through demonstration? And what else does demonstration do than [provide] a notion of the affection concerning its subject? Therefore, a science ought to have a subject about which it presupposes what it is, and about which it demonstrates its affections through principles believed within the science itself. It will become clear to all that our judicial [astronomy] is such if they understand with an impartial mind what we have said about astronomy. We say, therefore, that if astronomy seems bipartite into demonstrative and judicial, it is nonetheless truly one science in the unity of its subject, receiving a division from the different affections demonstrated in the same science about the same subject; this will be easily understood by the intelligent from the immediately following [arguments]. Let us say, then, that the subject of astronomy is the celestial body in that respect in which it moves with regular motions, and in it are virtues, by which virtues and motions it is the cause of generation and corruption. Regarding this subject, the astronomer makes a supposition, for it is as if sufficiently proven by the natural philosopher; for the philosopher proves that celestial bodies are the cause of generation and corruption, and that if they are to be the cause of generation and corruption, it is necessary that there be regular motions in them, since the same thing, while remaining the same, is naturally apt to produce the same effect. And therefore, the first motion is not the cause of generation and corruption, but [rather the motion] around the oblique circle. For in this, it is both continuous and moves with two motions. The philosopher also proved that it is necessary for this inferior world to be governed by the superior. The astronomer, however, proceeding to a further demonstration, investigates these regular motions—what they are, how, and in what time they occur—concluding demonstratively through geometric principles what we have just stated. And he performs astronomy, which is called demonstrative, whose demonstrations are all most certain, just as they are mathematical, as you know perfectly well. To this, our current science immediately succeeds, as a part subsequent to the whole of astronomy; and this science undertakes to demonstrate concerning the virtues of celestial bodies: what they are, and how and when they are the cause of generation and corruption. The astronomer arrives at the knowledge of these a posteriori, just as it happens in other sciences; for the philosophers began to philosophize from wonder. The astronomer, therefore, seeing from things that this man dies by the sword, while that man ends his final day in luxury, and believing that all of that proceeds from celestial bodies, began to investigate the causes of this diverse death. He found that such a star, disposed in such a way, granted this one a luxurious death, while it handed over a cruel death to another; and from many experiences, he constructed a science, according to that of the philosopher in the prologue of the Metaphysics: “Experience, indeed, made art, but inexperience, chance.” But it is an art when, from many experimental conceptions, one acceptance is made concerning similar things, whence he demonstrated from the “that” to the “what it is.” Wherefore it is manifest that the judicial astronomer uses both demonstrations: a priori indeed when he judges of future events—for then he proceeds from the cause over the effect; he uses a posteriori demonstration, however, when he brings forth judgment concerning things past—for then he syllogizes from the effect over the cause.

I believe it to have been sufficiently demonstrated up to this point, my Domenico, that this part of our astronomy, which we call judicial, ought most worthily and deservedly to be called by the name of science. For it will be easily shown why it should be called speculative if we posit the division of the sciences and clarify what “speculative” and what “active” or “practical” import. Let us say, therefore, with Avicenna in the first chapter of the beginning of his Metaphysics, that the sciences are divided into speculative and active. And the speculative are those in which the virtue of the speculative soul is sought to be perfected through the acquisition of science in effect, namely, through the attainment of imaginative and creditive science concerning things that are not our works nor our dispositions; in these, therefore, the end is the certainty of judgment and opinion. For judgment and opinion are not from the quality of our work nor from the quality of the beginning of our work, according to how it is the beginning of the work. The practical, however, are those in which the virtue of the speculative soul is sought to be perfected first through the attainment of imaginative and creditive science concerning things that are our works, so that secondarily the perfection of practical virtue may be reached in morals. It is manifest from these that the practical and the speculative are not distinguished from the part of the intellect, since both the speculative and the practical must perfect the virtue of the speculative soul, but [the distinction] is from the part of the thing considered and from the part of the end. Whence, if a science ought to be named practical, it is one that is about things that are our works or our dispositions, so that the perfection of practical virtue may be reached in morals. Just as the moral and the civil are. For what is moral among one people is vicious and reprehensible among another, as is manifest among the Epicureans; we see the statutes of cities similarly to derogate from civil law, and only the Emperor can derogate from the law. Canon law, therefore, could be changed entirely by a new council, and only the Pope can derogate from it. Nothing of these things can happen in those things that are considered by the speculative sciences. Avicenna subsequently adds that the speculative [sciences] are divided into natural, doctrinal, and divine, wishing that all other sciences should be comprised under these three, whence our astronomy will also be of the number of these, as I shall show more broadly below. But since we are also physicians and have broken into this discourse, we wish to insert what we think about our medicine itself. We say, therefore, briefly, whatever others may think, that according to the intention of Avicenna, it is to be counted among the number of the speculative [sciences], as can be made clear from these things that have now been said. For the speculation of medicine is about those things that are not our works nor our dispositions, nor does the perfection of practical virtue in morals result through it. The Prince [Avicenna] understood this same thing in the first [book] of the Canon at the beginning when he determined all of medicine to be a science, although many expositors attempt to extort their own opinion there. And in the third [book] of the Canon, at the beginning, he said that medicine in the first division is divided into two parts, into the theoretical part and the practical part, which, however, are all sciences of speculation. But if anyone asks under what mode of division it is contained, we answer that it is about natural things. This is clear from the number of sciences which the same Avicenna places in the same chapter of the Metaphysics when he shows God not to be the foundation of any science, just as neither is Metaphysics, where, counting all sciences except Metaphysics, he said that other sciences are either moral or civil or natural or doctrinal or logical, and no science of wisdom is from this division. It is evident, therefore, to one running through the divisions, that medicine is of the number of the natural [sciences]. And the same [author] in that same chapter says the subject of natural sciences is bodies as they move and rest, and what is inquired about them is the accidental things that belong to them properly according to this mode. It cannot be denied that both the subject of medicine and the accidents of it considered by it proceed according to this reason which he stated. Add that that science is to be called natural which speculates on the natures of the things pertaining to them, such as we all know medicine to be; therefore, medicine also is natural and speculative. Having brought in these very few things, therefore, about medicine, let us return to where we digressed, saying that astronomy, of which is our discourse, is to be counted among the speculative sciences. For it is about those things that are not our works nor our dispositions, nor is the perfection of practical virtue in morals to be attained through them. For what man or what nation can vary the celestial motions, or change the natures of the heavens and stars themselves, and prohibit their influences? None of these things can be done among men.