Astrology is a science which has had an uncertain status throughout its history, from its beginnings in Greco-Roman Antiquity to the medieval Islamic world and Christian Europe which led to frequent debates about its validity and what kind of a place it should have, if any, in various cultures. Written in the second century A.D., Ptolemy’s Tetrabiblos is not the earliest surviving text on astrology. However, the complex defense given in the Tetrabiblos will be treated as an important starting point because it changed the way astrology would be justified in Christian and Muslim works and the influence Ptolemy’s presentation had on later works represents a continuation of the method introduced in the Tetrabiblos. Abū Ma‘shar’s Kitāb al-Madkhal al-kabīr ilā ‘ilm akām al-nujūm, written in the ninth century, was the most thorough surviving defense from the Islamic world. Roger Bacon’s Opus maius, although not focused solely on advocating astrology, nevertheless, does contain a significant defense which has definite links to the works of both Abū Ma‘shar and Ptolemy. As such, he demonstrates another stage in the development of astrology. These three works together reveal the threads of a trend of a rationalized astrology separated from its mythical origins which began with Ptolemy and survived through both medieval Islam and medieval Europe. In the two examples of defending astrology I have used, Abū Ma‘shar and Roger Bacon, Ptolemy’s influence can be seen to have persisted from the second century through to the thirteenth, and the nature of the differences in their defenses illustrates the continuation and evolution of the tradition of defending astrology.

Astrology is a science which has had an uncertain status throughout its history, from its beginnings in Greco-Roman Antiquity to the medieval Islamic world and Christian Europe which led to frequent debates about its validity and what kind of a place it should have, if any, in various cultures. Written in the second century A.D., Ptolemy’s Tetrabiblos is not the earliest surviving text on astrology. However, the complex defense given in the Tetrabiblos will be treated as an important starting point because it changed the way astrology would be justified in Christian and Muslim works and the influence Ptolemy’s presentation had on later works represents a continuation of the method introduced in the Tetrabiblos. Abū Ma‘shar’s Kitāb al-Madkhal al-kabīr ilā ‘ilm akām al-nujūm, written in the ninth century, was the most thorough surviving defense from the Islamic world. Roger Bacon’s Opus maius, although not focused solely on advocating astrology, nevertheless, does contain a significant defense which has definite links to the works of both Abū Ma‘shar and Ptolemy. As such, he demonstrates another stage in the development of astrology. These three works together reveal the threads of a trend of a rationalized astrology separated from its mythical origins which began with Ptolemy and survived through both medieval Islam and medieval Europe. In the two examples of defending astrology I have used, Abū Ma‘shar and Roger Bacon, Ptolemy’s influence can be seen to have persisted from the second century through to the thirteenth, and the nature of the differences in their defenses illustrates the continuation and evolution of the tradition of defending astrology.