What seems to have happened during the confrontation between the receiving Islamic civilization and the imported Greek tradition, which we know was very closely watched by various sectors of the society, was to subject this incoming tradition to all sorts of exacting criteria before it was allowed to survive the cultural critique to which it was subjected. In that context, astronomy was no longer a discipline that only supplied good answers about the positions of the planets, or good enough answers for an astrologer to cast a horoscope. But with the Islamic religious aversion toward astrology itself and toward the craft in general, astronomy had to define itself as a discipline that went beyond that simple predictive feature and had to pose itself as raising questions of much greater relevance to a wider and larger world view that required exacting measures at every turn. The astronomer had to attend to all larger intellectual questions that had any bearing on his craft. In that concern the astronomer could no longer afford to seem as if he was satisfied with a confused picture of the universe, as long as he could achieve reliable results for astrological prognostications. Astronomy had to prove its usefulness to the new social and cultural environment within which it had to struggle. It could only do so by engaging the theoretical criticism of the very foundation of Greek astronomy.
In that context, one can then understand why no one could continue to tolerate two different visions of the nature of the universe that were in direct conflict with one another. One could not isolate the results presented in the Almagest, as mere computational and mathematical tools that could predict the positions of the planets at specific times, and say that they were irrelevant to the physical universe presented in the Planetary Hypotheses. To be fair, Ptolemy never really claimed that. On the contrary; throughout the Almagest he repeatedly hinted to the necessity of keeping the universe of the Planetary Hypotheses in mind. But at the same time he still went ahead and violated almost every feature of that universe by representing it with mathematical concepts that were totally divorced from their very mathematical properties. The example of the equant spoke directly to this point, where the spheres of the Planetary Hypotheses lost their very properties of spheres, if one were to represent them only in the manner in which they were represented in the Almagest.
With those fundamental oppositions, the job of the astronomer in the receiving Islamic culture became focused on those very issues of consistency between the vision of the Planetary Hypotheses and the representations of that vision in the Almagest. In the first phase of the response to the Greek astronomical tradition, the problem was perceived as a problem of sophisticating the techniques of representation, that is, the deployment of the same mathematics that was used by Ptolemy in order to reconfigure the representations so that they would be more faithful to the objects that they were representing. Someone like Abū 'Ubayd al-Jūzjānī (d. ca. 1070), the famous student of Avicenna (d. ca. 1037) did just that in his failed attempt to reform the representation of what later on became the equant problem. It took about two centuries to realize that Ptolemy's mathematics itself was inadequate, and that new mathematics had to be invented for the purpose.
The works of 'Urḍī and Ṭūsī ushered in the second, more important phase, when they spoke directly to that need of creating new mathematics. And each of them had a new theorem to add. Several astronomers, who used the newly enriched mathematics, and who also began to speculate about the various ways with which the physical phenomena could be mathematically represented, followed them. The nine attempts at representing the motions of the planet Mercury, which were devised by Ṭūsī's student and colleague Quṭb al-Dīn al-Shīrāzī, and the later attempt by 'Alā al-Dīn al-Qushjī to produce one more model for the motion of Mercury, fall in that category. This trend of re-defining mathematics as a language to describe the physical phenomena was to reach its climax with the works of Khafrī who finally gave concrete examples of four different mathematical models that described the motions of the planet Mercury, and yet were all exactly mathematically equivalent. In this fashion he could demonstrate, although never stated explicitly as such, that such physical phenomena did not yield unique mathematical solutions, but almost as many as the human imagination could conjure up, in exactly the same way a specific fact could be describe by an endless variations of the language.
With Ibn al-Shāṭir, the reorientation of astronomy took yet another turn, going back to the very cosmological foundations that were at the base of all phenomena as well as to the representations of those phenomena. Ibn al-Shāṭir ended up re-questioning the very use of the concept of eccentrics, and finding it cosmologically inconsistent with the cosmological foundations it was supposed to represent. When faced with the inevitable alternative of the epicycle, he insisted that such a tool be used despite the fact that the then current Aristotelian interpretation of his time thought of the epicycle as alien to the Aristotelian universe. Instead of giving up and pleading human imperfection, as was done by Ptolemy when the latter failed to find representations that were consistent with his own cosmological presuppositions, Ibn al-Shāṭir went back to the Aristotelian universe itself in order to criticize its inconsistencies and to point to the fact that such epicycles were, in a strict sense, consistent with an Aristotelian universe if the latter was properly understood.
Having banished all eccentrics in his representation of planetary motion, and having seen the essential similarities of all such motions in that they could all be represented by the same kind of model with a minor additional adjustment for the planet Mercury, Ibn al-Shāṭir went on to re-examine the relationship between the observed phenomenon and the mathematical models that were supposed to represent it. His readiness to adapt his mathematical models to match the observations speaks volumes about his priorities and about his ultimate re-definition of astronomy. To Ibn al-Shāṭir, astronomy was first and foremost a discipline that produced a systematic and accurate description of the behavior of the real universe around us. That description itself had to be a scientific mathematical representation that could only be a statement that described the reality of the observations.
Seeing these developments in Islamic astronomy in this fashion allows us to see how demanding the receiving culture was, and how its very demands required that its own scientific thought continued to be progressively defined and perfected according to the ever-changing criteria of precision and consistency that this culture imposed upon itself.
5. Science between Philosophy and Religion: The Case of Astronomy
The previous chapters focused on the social, political, and economic conditions that gave rise to and sustained science in the Islamic civilization. We had a chance to draw very broadly on the historical as well as the scientific sources themselves in order to illustrate with particular examples how these processes of motivation and encouragement as well as reward worked in order to enable certain scientific disciplines to be born, others to be abandoned, and still others to be maintained and reconstructed. We hinted several times already that we used the discipline of Astronomy only as a template simply because there was a methodological need to anchor the historiographic suggestions in a particular discipline in order to contextualize the much harder to document social forces at work.