Tetrabiblos (The Quadripartite Book)

... [It concerns] the name of its author. Concerning what art it is. Of how many parts it consists. Of the manner in which it demonstrates that which is in it. Of the reasons of which it speaks. I say that Ptolemy placed in it all the rules and roots by which this art is composed in judgments, so that whoever knows and understands them well will be able to say at any time those things which happen to all bodies that are below the sphere of the moon, from those things which they contain by nature and the accidents that follow them. And yet a man can know from this only as much as human intellect can reach.

Concerning the name of the book, I say that when Ptolemy looked into these rules and reasons, he found them to be of diverse manners; and on account of this, he placed each one in its own part. And he saw that there were four manners; wherefore he placed them in four treatises so that each might be by itself, in such a way that each could be called by its own proper name. And on account of this, he imposed upon this book the name of the book of the four parts of the judgments of astronomy, so that we may know that this science is divided into four parts, which he will state.

Concerning the profit of this book, I say that it is a thing which can be well understood by the reason of which it speaks in the name of the book, for from this book a man can know this whole science in a few summaries.

Concerning the ordering of the book, I say that the principles and roots are from the astrology which is accepted as divine, by which a man knows the motions and configurations of the stars, and similarly from the art of natures, by which a man knows the natures of things and their comprehensions. And on account of this, it is fitting that this book be read after these two sciences. It is also fitting that this book follow the quadrivial astrology, so that the knowledge may come in an ordered fashion.

Concerning the name of the composer, I say that it was Ptolemy Pelusiensis, that one who made the Almagest. And we intend this to be so, because his sense and intellect regarding the words of this book are assimilated to his sense in the words of others which he said in all the other books which it is manifest that he made. And it is of the manner in which he was accustomed to speak, for all the books which he made are of one likeness in their possessing, namely, great truth in knowing natural things as well as quadrivial ones, and in the ability to comprehend great reasons in few words. Furthermore, we find in other books which he made that he names and confesses this science, just as he said in his book on the highest states of the stars, that on account of the configurations of the stars touching them through their own motions, all the diverse mutations are made in quantity and quality in this world of generation and corruption, and on account of these configurations, mutations are made in the subject things of this world.

He also said in that book that celestial bodies give to the things below them, existing under them, virtues similar to the things themselves, having a natural aptitude for receiving them; and such a reason as this is, he said in many places of his book, the Almagest, as he reported in the book of his, for he spoke of the triple quadruple [operation] and conjunction, so that if we look diligently into these two books of his, we shall see them to be very similar in their reasons. And he said such words also in his book on aspects, and the words which he said in his book on the map of the world are also assimilated to those which he said in the second treatise of this book, for he spoke of the partition of the habitation of the earth. And the testimony of the ancient captains of Alexandria and other wise men of that time affirms this same thing, acknowledging that Ptolemy made this book, he who composed the Almagest; and other wise men who were after these, such as Thebit aben Cora, Jacob Alkindus, Iobanicius the son of Isaac, and Abzaaz de Abenagald, all affirm and are certain that Ptolemy Pelusiensis, who composed the Almagest, made this book. And if he had not made it, who would have been among the wise men one who would have such virtue in sense and wisdom in making such a book as this is, unless it were only this Ptolemy? Certainly, I do not think that anyone would be so ignorant or so bold that he would wish to make us believe that another made it, except this good man.

Yet Albumasar and others who made chronicles say that they did not understand except the text, and they accept things by hearsay, because they do not seek what is the truth or what is not, and they believed that this Ptolemy was one of the kings of Alexandria, from among those who were after Alexander, because all those emperors were called by such a name. And that there was among them one king who, however, loved wise men, wisdom, and sciences, and who profited and had as many books as he could of every manner of sciences. And as many wise men as he could, he drew to his land by prayers and great gratitudes which he bestowed upon them, so that Ptolemy was called the lover of sciences. And this Ptolemy

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was a long time before that Ptolemy who composed this book. For in all the chronicles we find that those kings of Alexandria who were called Ptolemy were before the Roman emperors. And we find that this Ptolemy who composed the book Almagest names the locations of the stars by their rectification in the time of the Roman emperors, much after the times of the kings of Alexandria. Wherefore we understand that this Ptolemy Pelusiensis was not one of the kings of Alexandria. Furthermore, we never find that this King Ptolemy, the lover of sciences, composed any book. Yet he loved wise men very much, and to hear sciences, and especially books on the Abzaica. And Johannes Grammaticus, who was one of the good wise men of Alexandria, affirms this which we say. Wherefore we find for certain that Ptolemy Pelusiensis, he who composed the book Almagest, made this one.

Concerning what science this book is, I say that it is of the science of prognostication, by which a man can know things which are to be in the future before they are, just as physicians know through signals which they possess whether a sick person will be able to be healed or not, or if a healthy person can come to sickness or not, or to what infirmity he is destined to come, just as you will find in the book of prognostications of Hippocrates, and in his book of airs, waters, and regions, and in the book of Galen on crisis, and in that on the critical days. Similarly, laborers in mines or at sea have their art which they understand through the rising and ascent of the stars and their setting, and through the winds which move, and they know those things which ought to happen in trees, harvests, and mines, and that which will happen to ships at sea, and what kind of time it will be. And the diviners have their art by which they know future things, by looking into hearts, shoulders, and the livers of beasts. Similarly, augurs and those who look to proverbs, because they are much accustomed to one thing through mysteries, have their own, namely, each one his own intention through knowing things which are to be in the future before they are. Wherefore, the science of prognostication is of many manners; we shall say that this art of astronomy is one among them. And we shall understand beforehand that it is more certain than all others, and truer and more general, and complete in all things.

Concerning the major parts of the book, I say that there are four, as it has been said. When Ptolemy looked into the general manners, he found that there were four. In the first part, he compiled all the general rules containing all the other parts of this science. In the second part, he compiled the rules by which a man can know great and general things which are to happen to many peoples or to a whole nation, such as the renewal of laws, new kingdoms, great wars, good or bad times for victuals, and great lands, and similar great things that are to happen in great lands; and of these he placed the second part. In the third part, he compiled all the rules by which one can know those things which are to happen to any person himself according to his nativity; and of this he composed the third part. In the fourth part, he compiled all the rules by which a man can know those things which are to happen to any person regarding extrinsic things, such as marriage, ministry, and such like; and of these he composed the fourth part. And after he divided this science into four general parts, it was fitting that each of them should have special chapters, as you will also find here. And that elections and reasons a man can understand through these things which have been said, Ptolemy did not wish to occupy himself in speaking of them, and all the more so because they are very weak things.

Concerning the manner of demonstration, I say that Ptolemy spoke in six manners: in composition, in solution, in partition, in definition, and in induction, and the like. That he spoke in composition and solution is like when he said that such a planet when it is by itself shows such a thing, and when it has another partition, it demonstrates such a thing; and thus, just as he demonstrates each thing by argument or by experience. In partition, as when he said that the common degrees of the zodiac are coincidental, having such and such a figure. In definition, it is as when he spoke of the division of the planets and signs. In induction, it is as when he spoke of the complexions of each planet, and as it was found by proof. In similarity, as when he demonstrates his reasons by similarity to others. But in all these manners he always speaks according to nature, such as heat, coldness, dryness, and humidity, and such natural things. For his operation is that all the stars effect these things in bodies which are below the sphere of the moon, and all other things follow them which are sought in this science, as you will understand later on. After we have completely stated the eight principal things, we wish to begin.