This was not a criticism of Ptolemy. Rather, it was an extremely well- articulated condemnation of the very foundation of Ptolemaic astronomy and an open call for its toppling in favor of an alternative astronomy that did not suffer from such contradictions. It did not only expose the fatal mistakes and contradictions in Ptolemaic astronomy, but rose to the occasion of articulating a new set of principles upon which an alternative new astronomy had to be based.
Such attacks, articulated by various astronomers working in the Islamic tradition, did in fact constitute an essential shift in the very conceptualization of the new Islamic science that was being articulated. The new conceptualization did not only condemn the Greek legacy, but laid the foundation for the new consistent science. In the new science, which was then born out of those attacks during Islamic times, physical objects would be, from then on, mathematically represented by models that did not deprive them of their physicality as was done by Ptolemy.
Ptolemy's latitude theory, as expounded in the Almagest, did not fair any better. In it Ptolemy himself had expressed doubts about its exact workings, an admission that only encouraged Ibn al-Haitham to conclude:
This is an absurd impossibility (muḥāl fāḥish), in direct contradiction with his [meaning Ptolemy's] earlier statement about the celestial motions—being continuous, uniform and perpetual — because this motion has to belong to a body that moves in this manner, and there is no perceptible motion except that which belongs to an existing body.[197]
What Ibn al-Haitham was referring to was the seesawing motion of the inclined planes, which carried the epicycles of the lower planets of Mercury and Venus. That motion was also another impossibility that could not be tolerated by Ibn al-Haitham, and was simply dismissed as another grave error on the part of Ptolemy. Ibn al-Haitham's argument can be summarized as such: with such motions Ptolemy was forcing physical bodies to move in opposite motions, which was in itself physically impossible.
Over and over again, Ibn al-Haitham returned to the vision of the new astronomy he would like to see—an astronomy based on the new principles of consistency between the physical reality of the universe we live in and the mathematics one uses to represent that reality. In the new astronomy, those two fields of science had to be constantly consistent, otherwise we would end up talking about imaginary motions as was done by Ptolemy:
The contradiction in the configuration of the upper planets that is taken against him [meaning Ptolemy] was due to the fact that he assumed the motions to take place in imaginary lines and circles and not in existent bodies. Once those (motions) were assumed in existent bodies contradiction followed.[198]
Furthermore, Ptolemy knew very well that he was embracing such contradictions as he was quoted by Ibn al-Haitham to have said: "We know that the use of such things is not detrimental to our purpose, as long as no significant excesses are introduced on account of them."[199] To which Ibn al-Haitham could only say:
He means that the configuration that he had posited necessitates no excesses in the motion of the planets. This statement, however, should not be an excuse for assuming false configurations (hayat bāṭila) that could not possibly exist. For if he assumed a configuration that could not possibly exist, and if that configuration anticipated the actual motions of the planets as he had imagined, that would not release him from the fault of having erroneously assumed such a configuration. For it is not permissible to stipulate the actual motions of the planets by a configuration that could not possibly exist. Neither is his statement regarding the assumption of things that are contrary to the accepted principles, that they are only hypothetical and not real and thus are not detrimental to the motions of the planets, an excuse that would allow him to commit such absurdities (muḥālāt) that should not exist in the configurations of the celestial bodies. Moreover, when he says that 'things that are posited without proof could have only been reached through some scientific mean, once they are shown to agree with the observable phenomena, even though it is difficult to describe the method by which they were reached' is a valid statement. By that I mean that he had indeed followed some scientific mean when he assumed what he assumed by way of configurations. Except that the mean that he had followed had led him to admit that he had assumed things that were contrary to (the accepted) principles. Once he knew that it was contrary to the principles, he had no excuse to assume it, saying that it was not detrimental to the motions of the planets, unless if he were prepared to admit that the real configuration was different from what he had assumed, and that he could not reach its essence. Only then would he be excused to do what he did, and it would be known that the configurations that he had assumed were not the real ones.[200]
In this long passage, Ibn al-Haitham leaves no doubt as to his real intentions. He obviously means that real physical bodies do exit in the universe and once that was assumed those bodies must be represented by mathematical models that did not violate their true physical nature, as was done by Ptolemy when he assumed the existence of an equant that would force a physical sphere to move uniformly, in place, on an axis that did not pass through its center. That was physically absurd in Ibn al-Haitham's new astronomy.
In the larger cultural context, this passage also demonstrates the extent to which these cosmological debates began to influence the very foundation of science; they allowed for the new requirement of consistency to be clearly demonstrated with such vivid examples from the field of astronomy.
The timing of those remarks is also important, for they allow us to conclude that the eleventh century, which has produced so many critiques of Ptolemaic astronomy as we have already seen, seems to have been the time when new research projects were launched, and new re-organization of the sciences on new conceptual grounds must have begun to take place. The appearance of the new disciplines of mīqāt, and farā'iḍ, soon after that or very close to that time, are only few of the features that must have characterized this period. Similar results can be derived from an analysis of the developments in the mathematical and medical disciplines, and those who work in those fields may also reach similar conclusions. For astronomy, this vigorous discussion of the foundations of science seems to have given rise to long-term developments whose repercussions eventually led to truly revolutionary results. Those results, in turn, led to the final overthrow of the Greek astronomical edifice.
199
Ibid. In similar wordings this admission was in fact made by Ptolemy in