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Alcabitius (or Alchabitius) is the Latinised name of the Muslim astrologer al-Qabisi (named after his birthplace, the village Qabisa in Iraq).1 Al Qabisi's birth date is unknown, but he flourished in the mid-10th century in Aleppo, Syria, and is widely reportedly to have died in 967.2 Details of his death are not documented, however, so this date may simply have marked his retirement, 967 being the last year in which he dedicated a work to Aleppo’s ruler, Sayf al-Dawla, whose reign ended that year. The dedicated works to Sayf al-Dawla began in 945 AD, so Al Qabisi is known to have been active at a high level of prominence for at least the full 22 years of Sayf al-Dawla's reign.3

Most astrologers are familiar with the name of Alcabitius due to the house system attributed to him. Al Qabisi did not invent that system of house calculation but personally employed it and explained it in sufficient detail that references to it in the late Middle Ages generally credit him as their source. In his own time, it was already considered ancient, and was widely attributed to Ptolemy because its calculation was facilitated by the tables of ascensional differences in Ptolemy’s Almagest (II.7) and by astrolabes dependent on information presented in Ptolemy’s Planisphaerium.4 (The oldest clear explanation of how to calculate ‘Alcabitius’ house cusps is found in a chart attributed to Rhetorius, dated 428 AD, although as J.D. North reports “the key to the calculation had been available to the Babylonians”.)5



Al Qabisi had expert knowledge of the works of Ptolemy and wrote commentaries on many of them, as well as his own summary of the Almagest supplemented with Arabic tables. He also compiled test materials for would-be astrologers, which required a ‘complete astrologer’ to understand the astronomical principles in the Almagest so well that they could manually calculate planetary placements, movements and aspects without recourse to any books or tables. The tests also required them to realise the principles that underpin the knowledge, and not only know the astrological techniques by heart but also understand the relation of one astrological technique to another. He bemoaned that his prince, al-Dawla, was “surrounded by people who call themselves ‘astrologers’, among whom some are competent, others incompetent, and others, out of deceit, only pretend to be astrologers”.6

The fact that a house system he did not invent is ascribed to this scholar testifies to his respectful stature as a well-informed astrologer and to the influence of his work as a source for astrological study from the early medieval era onwards. His most influential text is an introduction to natal astrology entitled al‐mudkhal ilā ṣināʿat aḥkām al‐nujūm, ‘The Introduction to the Art of Astrology’, comprising of five parts:

• The essential and accidental conditions of the zodiac
• The natures of the seven planets
• Explanations of how planets are modified accidentally and by aspects with each other
• Explanations of technical terms
• The planetary Parts (Lots)

Al-Qabisi’s Introduction was widely used as a university textbook for many generations, in both the Arabic-speaking nations and the Latin West. For that reason, it has been well preserved, surviving in at least 25 Arabic manuscripts and over 200 Latin manuscripts. Its popularity in the 15th and 16th centuries led to twelve printed editions being released between 1473 and 1571.5

The first Latin translation was produced around 1140 by John of Seville (a.k.a. Johannes Hispalensis) under the title Opus Isagogicum or Liber Introductorius. Due to its influence and academic importance, a market soon developed for commentaries, the most important being that of the German-born Parisian lecturer, John of Saxony, who flourished in the late 12th to the mid-13th century.

The 1512 edition shown below includes Saxony’s commentary and was first published in Venice by Melchiorre Sessa. This is available to view or download, along with other important medieval Latin astrology texts, on the Library of Congress website.

Illustrating why Alcabitius’ work was so innovative and influential, Richard Kay1 says of his discussion on the planets:



And from Bonatti, it passed into the details of planetary significations listed in Lilly’s Christian Astrology ... and through Lilly it continued to transmit, and will continue passing forward – although Alcabitius would surely be spinning in his grave if he knew how few astrologers nowadays would pass his ‘complete astrologer’ test.