But before recounting the examples of the hay'a writers who also served as religious scholars, it is important to remember that the religious critiques not only produced two other scientific disciplines ('ilm al-farā'iḍ and 'ilm al-mīqāt) but had a general impact on the other sciences. The simple requirement of having to face Mecca, every time one prays, definitely required the solution of one of the most sophisticated spherical trigonometric problems of the time, known as the qibla problem. The qibla, being literally the direction one must face while praying, and knowing that the globe is supposed to be spherical, meant that one had to solve for the angle his own local horizon makes with the great circle that passes through his own zenith and the zenith of Mecca. That calculation itself requires the deployment of such trigonometric functions as the sine, cosine, tangent, and cotangent. It also meant the development of the equivalent trigonometric laws that apply to the surface of the sphere.[286]
Such kinds of trigonometric functions were not known in the Greek tradition, and the ones that were known from the Indian tradition were insufficient to solve the problem completely. As a result a whole series of trigonometric laws, like the spherical sine and cosine laws, had to be developed anew. Once that was done, there was little left to discover in the field of trigonometry.[287] One can then say that such a religious commandment, despite its apparent simplicity of requiring the believers to simply face a specific direction, was one of the reasons that gave rise to a most sophisticated discipline of spherical trigonometry. This new discipline in turn became subservient to other religious requirements, as much of it was used in almost every branch of mīqāt literature.[288] It also served the mother discipline of astronomy just as much, and without it, much of astronomical research, till this very day would have remained cumbersome if not impossible to conduct.
In short, the discipline of trigonometry is the best example that demonstrates the intersecting interests between the practice of one's religion and the scientific thinking that had to be developed as a result of that practice. With this in mind, and seeing how scientists, and astronomers in particular, could pose as the experts for the practice of the religious prescriptions, it should not be surprising to find scientists at this epoch closely affiliated with the religious functioning of the society. At times they were even at the helm of religious offices themselves, as we shall soon see.
In another scientific field, quite different from astronomy, we also find a rapprochement between the religious precepts and the scientific practice. In a field such as medicine, where religious thought had laid great emphasis on the need to keep a healthy body,[289] and one could quote several sayings of the prophet himself attesting to that interest, it is very difficult to miss the relationship between medical and religious practice. As a result, it should not be surprising as well to find famous physicians practicing their religious functions at the same time, and at times lending as great an authority to their religious practices as they would do to the medical one. To confirm that close association no one is surprised to find the famous Ibn al-Nafīs (d. 1288), the author of the critical commentary on Avicenna's Canon in which he criticized Galen regarding the functioning of the heart, which in turn led to the discovery of the pulmonary movement of the blood, being at the same time a practicing Shāfi'ī lawyer, who even gave lectures on Shāfi'ī law at the Masrūrīya madrasa.[290] In light of what we know about the status of medicine in Islamic society, joining these two functions should not require any further explanation.
Returning to the astronomers, and in particular to the theoretical astronomers, whose works have been designated so far as hay'a works, one should expect to find the same close association between their scientific functions and their religious ones, especially when they had already formulated their new astronomy of hay'a specifically to cast astrology out of the domain of astronomy and to respond to the religious pressures of the society. In the new configuration, theoretical astronomy, which became the domain of hay'a studies, became a close ally of religious thought. At one point, during the Iranian Safavid period and thereafter, it became another subject of religious instruction. In a separate publication I have argued for the interpretation of the phenomenon of the continuous use of the Arabic language in the production of hay'a texts, even when the native language of the writers was Persian, as a phenomenon of integrating astronomy into the school curriculum. These school curricula had always weighed heavily in the direction of Arabic as the language of the primary religious texts.[291] From interviews with graduates of modern day Iranian seminaries, my understanding is that this incorporation of hay'a texts in the religious school curricula still goes on till the present day.
With this alliance, it is not surprising to find one of the most productive astronomers, the same Naṣīr al-Dīn al-Ṭūsī (d. 1274)[292] who produced the famous Ṭūsī Couple in the context of his attack on Ptolemaic astronomy, being at the same time a great Ismā'īlī scholar first and then an acknowledged authority on general Shiite thought. His own spiritual autobiography Sayr wa-sulūk,[293] as well as his doctrinal text Rawḍat al-taslīm,[294] speak directly to his authoritative status within the Ismā'īlī religious thought. His Awṣāf al-ashrāf[295] and his Tajrīd al-i'tiqād[296] also speak to his much more exalted status among the Sufi adepts and the twelver Shiites, respectively. To some (especially Shiite biographers not skilled in the astronomical sciences), he was primarily a religious figure who may have had a side interest in astronomy. His student and former colleague Quṭb al-Dīn al-Shīrāzī (d. 1311) also produced several voluminous works on theoretical astronomy, two of which were detailed commentaries on Ṭūsī's Tadhkira, with their own original contributions to the field. In addition, Shīrāzī also occupied the position of a practicing judge in the cities of Sivas and Malaṭiya, in 1282, after his affiliation with the Marāgha observatory, and while he was still writing his first commentary on Ṭūsī's Tadhkira.[297] He also acted as an intermediary between the Ilkhānids and the Mamluks, once the Ilkhānids had converted to Islam. His mission was obviously an exercise of his religious duty to bring peace between two warring Muslim potentates.
Shīrāzī's religious works are as impressive as his astronomical works. Since he had become a ḥadīth scholar in his own right, his book Jāmi' uṣūl al-ḥadīth naturally became one of the main references for this type of religious literature at this later period. And so did his work on the prophetic tradition sharḥ al-sunna. But his elaborate commentary on the Qur'ān, Fatḥ al-mannān fī tafsīr al-qur'ān, definitely attests to his wide-ranging control of the many religious disciplines of his time.
286
For a brief description of the development of the various solutions of the
287
Reviewing the general developments of the exact sciences, E. S. Kennedy had this to say about the discipline of trigonometry: "This subject, the study of the plane and spherical triangle, was essentially a creation of Arabic-writing scientists, and it is the only branch of mathematics of which this statement can be said." E. S. Kennedy, "The Arabic Heritage in the Exact Sciences", al-Abḥāth 23 (1970): 327-344.
288
For a short survey of the discipline and the use of trigonometric functions, see D. King,
289
A frequently repeated tradition from the prophet, as quoted by Shāfi'ī, says:
291
See Saliba,
293
English translation:
294
al-Ṭūsī, Naṣīr al-Dīn,