Ten Treatises on Astronomy (Book of Astronomy)

astrology is called the fourth part of the quadrivial science The Quadrivium consisted of the four mathematical liberal arts: Arithmetic, Geometry, Music, and Astronomy/Astrology.: if astrology itself does not exist, then the entire Quadrivium does not exist. Since, if an integral part is destroyed, or its integrity is compromised, the whole is destroyed—which is a most unfitting conclusion. Likewise, if the Quadrivium does not exist, mathematics does not exist; and if mathematics does not exist, then theoretical science does not exist, since mathematics is—according to the Philosopher Aristotle was often referred to simply as "The Philosopher" in medieval texts.—the third part of theory. Furthermore, if theoretical science does not exist, then philosophy does not exist, which is a stubborn, difficult, and absurd thing to say. Therefore, astronomy is by necessity a science. For he who destroys astronomy destroys science, just as he who destroys first principles destroys wisdom, according to Aristotle in the second book of his Metaphysics. One should not argue against such people who wish to destroy the sciences, for they are worse than beasts. Furthermore, since Aristotle, Ptolemy, Japhar, Agathodaimon, Albumasar, Masha'allah, Elmetus, Alfraganus, Thabit ibn Qurra, Sergis, Tibomar, Dorotheus, Al-Kindi, Albenait, Astaphaz, Al-Mansur, and many other wise men wrote and taught this science, it is not likely that astrology would not be a science when so many and such great men have named it as such. Likewise, everything that establishes something through a cause or through an effect establishes a science, as Aristotle testifies in the Posterior Analytics. The astrologer demonstrates an eclipse through its cause (namely, the interposition [of the moon]) and demonstrates that same interposition through the eclipse; for these and many other reasons, it is clearly proven that astrology is a science.

Here ends the first treatise in the confirmation of this science.

Here begins the second treatise on the division of the circle of signs, their nature, how they are ordered and arranged, why there are exactly twelve—neither more nor fewer—why they are denoted by those names, and regarding matters adjacent to these.

Therefore, following in the footsteps of our venerable predecessors, I am recording those things which will be seen as useful to this work, recalling their opinions—namely those of Ptolemy, Hermes, Japhar, Thabit, Al-Qabisi, Alcaist, Al-Kindi, Al-Encedego, Masha'allah, Adila, Sergis, Albenait, Agathodaimon, Aristotle, and others who have studied in this science—adding those things which seem useful to me, according as God shall grant me grace, order them, and bring them back to my memory.

Chapter One: On the division of the circle of signs, and that there are exactly twelve signs, neither more nor fewer.

Know this: that the circle of signs The Zodiac. is divided into twelve equal divisions, each of which is called a sign. The first of these is Aries. The second, Taurus. The third, Gemini. The fourth, Cancer. The fifth, Leo. The sixth, Virgo. The seventh, Libra. The eighth, Scorpio. The ninth, Sagittarius. The tenth, Capricorn. The eleventh, Aquarius. The twelfth, Pisces. But perhaps it could be asked why there are only twelve signs. For many reasons could be assigned as to why there are twelve signs, neither more nor fewer. One reason—though it is not very powerful—is that the number twelve is more perfect than almost all other numbers because its units do not exceed it, and the multiplications from which it arises are multiplied in its parts. For it receives within itself more ordered divisions than any other number: for it arises from the multiplication of three by four, and four by three; and of two by six, and six by two; and it is divided in as many ways by those same parts. There is another reason, no less powerful than the one above, according to what Aristotle, Albumasar, and Agathodaimon said (whom no philosopher has dared to contradict): namely, that all elementated things Things composed of the four physical elements.

are composed of the four elements: fire, air, water, and earth. And those "elementated" individuals and the parts of those individuals all consist of the aforementioned four elements. Within every individual being, these three things are present: a beginning, a middle, and an end. Therefore, four [elements] multiplied by three [stages] makes twelve. For the signs do not decay, but they cause decay in "elementated" things. The elements are four, and they are corrupted [changed] by the signs and planets through their unceasing circling. For otherwise, the elements would not decay insofar as they are in themselves, unless they were acted upon by the stars and their circling. For the circling of the stars around the elements decays them, and they decay one another; the more noble (the active forces) decay the less noble (the passive forces). Because of this, they embrace each other, which is the cause of the generation of individuals of every species. The signs were divided according to the number of the four elements, so that through the four elements—which are of four different natures or qualities—the number of the twelve signs might be understood. For one of the elements is hot and dry, namely fire. Another is hot and moist, namely air. Another is cold and moist, namely water. Another is cold and dry, namely earth. And although they say the elements are complexed, nevertheless each of them has only one primary property: for the property of fire is heat; the property of air is moisture; the property of water is coldness; and the property of earth is dryness. Therefore, it was necessary that the signs should be according to four diversities, impressing their influence on lower things: namely according to heat and dryness; heat and moisture; coldness and moisture; and coldness and dryness. Thus, three of these are called fiery: namely Aries, Leo, and Sagittarius. Another three are called earthy: namely Taurus, Virgo, and Capricorn. Another three are called airy: namely Gemini, Libra, and Aquarius. Another three are called watery: namely Cancer, Scorpio, and Pisces. And thus the signs were found to be twelve only, neither more nor fewer. There could not be more, because each of them acts upon the four elements universally, and each acts upon the element assigned to it according to three states: namely, the beginning, the middle, and the end. Since the signs act upon each element according to this threefold state, and there are only four elements, it was necessary for there to be exactly twelve signs, neither more nor fewer. As was said, Aries, Leo, and Sagittarius are fiery; Taurus, Virgo, and Capricorn are earthy; Gemini, Libra, and Aquarius are airy; and Cancer, Scorpio, and Pisces are watery.

Chapter Two: How the signs act upon the elements, and upon which elements each sign acts.

It was stated in the preceding chapter that the signs act upon the elements; now it must be said in this chapter upon which element each sign acts and in what manner. For Aries, Leo, and Sagittarius, which are fiery, act upon the element of fire, but in different ways.

Concerning Aries.

A woodcut illustration of a ram, representing the zodiac sign Aries, standing on a patch of earth.

Since Aries acts upon the element of fire, it infuses it with a tempered heat and dryness. However, that which arises from that tempering is the beginning of the natural movement of individuals of any species: namely, to the action of one animal with another, so that they may generate individuals of the same species from their own kind, so that the species may be saved through succession. For they would not be saved through individuals over a long time, because in the passage of time individuals would fail, and thus species would be destroyed and lost unless they were saved through [reproduction].