Bonatti, Guido

Bonatti, Guido

(religion, spiritualism, and occult)

The astrologer Guido Bonatti was born in Cascia, Italy, although his birthdate is unclear. We know he was in the Italian cities of Ravenna and Bologna, in 1223, and in Forli by 1233. He was advisor to Frederick II Hohenstaufen, the Holy Roman Emperor. In 1259, Bonatti entered the service of the tyrant Ezzelino III da Romano, and the following year he became astrologer to Count Guido di Montefeltro. Bonatti was the author of the Liber astronomicus sometime after 1282. He died in 1297. In History of Magic and Experimental Science (1923), Lynn Thorndike reports that Dante put Bonatti in the eighth circle of his Inferno: “Vedi Guido Bonattià”—Inferno, XX, 118.

Bonatti was a well known and influential man in his day and still highly regarded in Forli and Bologna. He was an aristocrat, an adviser to the mighty, and a learned man. The chroniclers of the day—Giovanni Villani, Fossi, Salimbene di Adam—took note of him. The Annales of Forli report that he played a prominent part in the defense of Forli in 1282 by Guido Montefeltro against a large force sent by Pope Martin IV. Despite the high regard he was held in during his lifetime (which continues in Bologna and Forli to this day, where Guido Bonatti has the status of a kind of local hero), there are few reliable details about his life. The date of his birth is a mystery. The year of his death is debated; Thorndike thinks it closer to 1300 than 1297. Bonatti is said to have ended his life as a Franciscan monk.

Bonatti’s role in the spread of astrology in western Europe in the thirteenth century was an important one. The twelfth century saw the western Christian world suddenly become obsessed with Arabic Science (called the “New Science”). Astrology played a central role in this New Science. The transmission of Arabic astrology to the Latin West and a renewal of interest in both Greek and Arabic astrology among the Byzantines led to translation projects, principally in Spain and Sicily, where translators worked avidly and prolifically to make Arabic astrological texts available to the Latins. The thirteenth century saw the widespread assimilation of this recently acquired astrological science and to ecclesiastical opposition to it. Astrology was condemned by the church in 1210, 1215, and 1277. These multiple condemnations show that no one was listening. Instead of giving up astrology, western Europeans were practicing it and comparing the many texts circulating in western Europe.

Bonatti’s Liber astronomicus is an outstanding exemplar of the thirteenth-century dissemination and assimilation in Christian western Europe of Arabic astrology. It is a Summa of astrology based upon the author’s collection, collation, comparison, and application of the existing Latin translations available to him. Bonatti was a practicing astrologer. In his day, his reputation was good.

Thorndike, in the History of Magic and Experimental Science calls the Liber astronomicus “the most important astrological work produced in Latin in the 13th century.” The same work is also known as the Liber astronomiae. Bonatti, like Roger Bacon, uses the word “astronomy” to denote what we understand as astrology and the word “astrology” to denote astronomy. His influence is attested to by the many manuscripts and printed editions of his work. It was widely circulated in manuscript and translated into Italian and German (Basel, 1572). Segments of the text have been translated into English: his 146 Considerations, Lilly (1676); Tractatus I, II, and III, by Zoller (1994), available from; and his dicta on how to wage war using astrological elections (in Tractatus VI). A manuscript copy was in the library of Italian humanist Giovanni Pico della Mirandola. English mathematician and astrologer John Dee also had a manuscript copy of it; Italian philosopher Marsilio Ficino must have had one as well.

Bonatti’s Liber astronomicus remained a standard work from the thirteenth to the eighteenth century. The English astrologer Alfred J. Pearce mentions Bonatti in his nineteenth-century Textbook of Astrology. Pearce’s citation of Bonatti underscores the importance of the Italian’s work and his lasting influence among serious astrologers. Pearce’s mishandling of Bonatti’s instructions regarding the keys to mundane astrological delineation and prediction are typical of the nineteenth-and twentieth-century corner-cutting simplification of real astrology, which produced a more provincial, nonthreatening astrology and opened the door to the blander version of astrology often found today.

To speak about Bonatti is to speak about his Liber Astronomiae. The work is 10 tractates long in 848 numbered columns (425 unpaginated pages in the 1550 Basel edition). It deals with horary, electional, natal, and mundane astrology. A text on astrometeorology is appended to the 1496 Venice and the 1550 Basel editions.

Tractatus Primus presents Bonatti’s philosophical argument in favor of astrology. He relies heavily upon Abū Ma’shar’s Greater Introduction. Tractatus Secundus gives the basics of astrology, signs, subdivisions, planets, houses, joys of the planets, dignities, melothesiae, and characteristics of degrees. Tractatus Tertius discusses the natures of the planets, how they interact with each other, the signs, and houses. Tractatus Quartus is on the consideration of certain conjunctions and of other things the astrologer ought to know. These things are the definitions of certain technical terms in astrology, the great conjunction of Saturn and Jupiter in the first term of Aries, the conjunction of the same planets in the beginning of each triplicity, the conjunction of Saturn and Mars, the conjunction of Saturn and Jupiter, the conjunction of the Sun with the other planets, the conjunction and opposition of the luminaries, the combust and incombust hours, the duodena of the Moon, and that the discovery of the ascendant when the birth time is uncertain is through the Animodar of Ptolemy.

Tractatus Quintus presents Bonatti’s 146 Considerations pertaining to judgment. In Tractatus Sextus, Bonatti talks about perfection in horary astrology (interrogations). Tractatus Septimus discusses the special judgments of the stars (horary astrology). Tractatus Octavus—Elections Tractatus Nonus covers revolutions of years (solar ingresses into the cardinal signs) and the Arabic Parts. Tractatus Decimus deals with the topic of natal astrology, while Tractatus de imbribus et aeris mutationibus deals with astrometeorology.

Like most ancient and medieval texts on astrology, Bonatti’s book has something to say about character analysis, but little about psychology. The emphasis is on the objective behavior of the native and others in the native’s life, with an eye toward predicting the external events (the accidents of the native) rather than the subjective response to them or to their alleged significance. The Liber astronomicus is concrete in its interpretations. The author is direct and does not mince words. He is usually forthcoming in his appraisal of his sources. He regards Abū Ma’shar as a prince of astrology and usually accepts the Persian astrologer’s opinion on most subjects. Bonatti generally arranges his discussion of astrological procedures by first presenting the reader with a detailed description of the astrological method and then bringing forward special cases and the opinions of the ancients. The fate of Bonatti’s Liber astronomicus is the fate of western astrology.

In the Renaissance, due in part to political and military realities following the fall of Constantinople to the Muslim Turks, and to Turkish occupation of the Balkans, there was considerable fear in western Europe that Christendom would fall under the Muslim Turkish control. An intense anti-Islamic response ensued in which all things Turkish, Arabic, and Islamic were repudiated. The intelligentsia, among whom the astrologers were to be counted, turned towards scientism, in particular to Copernicus’s heliocentricity, abandoning the geocentric astronomy of Ptolemy and Aristotle that had become by this time embedded in the Catholic worldview. Bonatti’s astrology, which had entered Western Europe as part of the “New Science” in the twelfth century, was now regarded as typical of the old Catholic cosmology by contemporary critics who sought a new New Science 300 years after the last “renaissance.”

As a result of the Turkish threat, the Reformation, the Thirty Years’ War, and the beginnings of the Scientific Revolution of the seventeenth century, western European intellectuals turned increasingly toward Greek science, secularism, scientism, and rationalism. Greek science, astrology, and mathematics were regarded as superior to their Arabic counterparts. As western philology demonstrated the adulteration of pristine Greek texts of Ptolemy’s Tetrabiblos, for instance, the Arabic astrology was increasingly regarded as corrupt.

Repudiated by the intellectually superior and educated, bona fide astrology à la Bonatti’s Liber astronomicus was ignored on the continent, as was the entire subject of astrology until the “Occult Revival” of the nineteenth century. Perhaps because it was used for propagandistic purposes during the English Civil War (1642–1646) and during the Commonwealth (1649–1660), astrology was preserved in England. Nevertheless, it was not the “papist” medieval astrology that survived, but a “reformed” and simplified astrology intended to make the science of the stars popular and, thus, politically useful. Later, in the eighteenth century, the almanacs made astrology accessible as entertainment to the partially educated.

Bonatti’s Liber astronomicus is an important resource for the practicing astrologer. From the point of view of the history of science, it may be viewed by some as an example of superstitious protoscience or pseudoscience. From the theological point of view, its contents, if put into practice, enable the astrologer to achieve a better than 80 percent accuracy. It thereby calls into question the doctrine of free will as it is held by religionists and by secular humanists. Philosophically, Liber astronomicus demands that the philosopher reexamine the conclusions of the Jewish and Arabic neoplatonists—Al-Farabi, Ibn Sina, ibn Gabirol, and Ibn Rushd. From the point of view of the practice of the art, it ought to be recognized that astrology in medieval Islam was and continues to be regarded as a traditional and sacred science subordinate only to the Koran. It was as such that astrology reentered western Europe in the twelfth century.

The Liber astronomicus allows for the recovery of much of what was ill-advisedly tossed out as “superstition,” “Arabic” (i.e., allegedly corrupt), and “papist.”

—Robert Zoller


Debus, Allen G. World Who’s Who in Science. 1st ed. Chicago: Marquis’ Who’s Who, 1968.
Halliwell-Phillipps, J. P., ed. The Private Library of Dr. John Dee, and the Catalogue of his Library of Manuscripts. London: Camden Society Publications, 1842.
James, Montague R. Lists of Manuscripts Formerly Owned by Dr. John Dee. Oxford: Bibliographical Society, 1921.
Kibre, Pearl. The Library of Pico Della Mirandola. New York: Columbia University Press, 1969.
Liber Astronomiae. Appeared in print in Latin first in 1491 at Augsburg. Radolt was the publisher (G.W. 4643). Other Latin editions were produced in Venice (1506), and Basel (1530 and 1550).
Thorndike, Lynn. History of Magic and Experimental Science, Vol. II. New York: Columbia University Press, 1923.
Zoller, Robert. “The Astrologer as Military Adviser in the Middle Ages,” Astrology Quarterly. (1992–93).