Arabic versus Greek Astronomy: A Debate over the Foundations of Science

This short note is occasioned by the publication of a review essay by A. I. Sabra in this journal, under the title "Configuring the Universe: Aporetic, Problem Solving, and Kinematic Modeling as Themes of Arabic Astronomy." Sabra's review itself was in turn occasioned by the recent publication of four books (all in the 1990s), two of which were written as dissertations by Sabra's own students and under his own supervision, and the last two were written by the present author.

As a review essay, Sabra's assessment of the books under consideration is rather fair, and as far as his assessment of the present writer's books is decidedly flattering, and, for all practical purposes, engaging enough to invite the reader to examine those books.

Had Sabra's essay review been only a review, however, it would not have been necessary to bring it once more to the attention of the readers of Perspectives on Science, except maybe to make a corrective statement or two whenever the essay strayed into error. But it proclaims to do more than that. In 52 densely printed pages, it attempts to determine the purpose and character of a whole tradition of astronomical writings that occupied a major place in Islamic civilization for slightly more than a millennium, from the ninth to the twentieth century, a Herculean task in itself.

The tradition in question was the one commonly known as the hay'a tradition, whose very name is still problematic since no one has ever been able to demonstrate that the term hay'a had any Greek antecedents. Its beginnings though can be incontestably dated back to the middle of the ninth century if not before, as is evident from the work Kitab al-hay'a (Book on Astronomy) by Qusta. b. Luqa (fl. 860), who was not mentioned in Sabra's essay. Its purpose, as I shall argue below, seems to have been an attempt to set new foundations for the science of astronomy, thus giving rise to the need to coin a new term for the discipline by calling it 'ilm al-hay'a (Science of the Configuration [of the universe] or simply Science of Astronomy in the "new" style for short). Needless to say, this discipline was not known before, and its new foundation was supposed to be distinct from the foundation that was laid down in the old astronomy, namely, that which was presented in Ptolemy's two major works, the Almagest and the Planetary Hypothesis.

Considering that Sabra's essay focused only on the published books under review, it stands to reason that it would miss some important findings from that tradition that have appeared in journal articles. One regrettable example is the work of the most brilliant astronomer of the Arabic tradition, a man by the name of Shams al-Din al-Khafri (d. 1550) (Saliba 1994b), whose work marks a watershed in that tradition by forging completely new grounds that were never approached by earlier astronomers, here I mean the manner in which he deployed mathematics to describe astronomical planetary theories (Saliba 1993b). When Khafri's work is put in context, one could then update Sabra's statement that Ibn al-Shatir (d. 1375) "represents the highest point so far known in the enterprise" (p. 317). This statement needs also to be updated by the addition of the equally impressive work of Qushji (d. 1474) as well (Saliba 1993a).

By returning to Sabra's essay the rest of this note will offer an alternative assessment to that proposed by Sabra in regard to the purpose of three well documented Arabic astronomical traditions: the hay'a tradition (well represented by the four books in the review) and described by Sabra as a problem-solving tradition [pp. 299, 300, 306, 322, et passim]; the zij tradition (with no representative book in the review) which continuously updated mean...