Thorndike, in the History of Magic and Experimental Sciencecalls the Liber
astronomicus“the most important astrological work produced in Latin in the 13th cen-
tury.” 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 manu-
scripts 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); TractatusI, II, and III, by
Zoller (1994), available from http://www.robertzoller.com; and his dicta on how to wage war
using astrological elections (in TractatusVI). 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 Fici-
no must have had one as well.Bonatti’s Liber astronomicusremained 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 mun-
dane astrological delineation and prediction are typical of the nineteenth- and twen-
tieth-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 Primuspresents Bonatti’s philosophical argument in favor of astrolo-
gy. He relies heavily upon Abu ̄ Ma‘shar’s Greater Introduction. Tractatus Secundusgives
the basics of astrology, signs, subdivisions, planets, houses, joys of the planets, digni-
ties, melothesiae, and characteristics of degrees. Tractatus Tertiusdiscusses the natures
of the planets, how they interact with each other, the signs, and houses. Tractatus
Quartusis 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 ascen-
dant when the birth time is uncertain is through the Animodar of Ptolemy.
Tractatus Quintuspresents Bonatti’s 146 Considerations pertaining to judg-
ment. In Tractatus Sextus,Bonatti talks about perfection in horary astrology (interro-
gations). Tractatus Septimusdiscusses the special judgments of the stars (horary astrolo-
gy). Tractatus Octavus—Elections Tractatus Nonuscovers revolutions of years (solar
ingresses into the cardinal signs) and the Arabic Parts. Tractatus Decimusdeals withBonatti, Guido
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