A Critique of the Arguments for Maragha Influence on Copernicus

Abstract

(ProQuest: ... denotes formulae omitted.)1. IntroductionCopernicus's planetary models exhibit some striking similarities to those of late medieval Islamic astronomers. On this basis many have concluded that he must have been influenced by them.1 We claim that no good evidence for this inference exists. Certainly there is no direct trace of it in the documentary record: the sources Copernicus supposedly copied from are not cited by him or any of his European contemporaries - despite the fact that Copernicus happily cites numerous earlier Islamic sources2 - and there is virtually no evidence that they were accessible to him.3As for the technical similarities, they are all natural consequences of natural principles, making independent discovery perfectly plausible. Copernicus and his Islamic predecessors had the same starting point, the same goal, and the same techniques at their disposal, so extensive similarities in their results are to be expected even if they worked independently. Nor is it surprising that they had the same goal, namely to reformulate Ptolemy's theory of the planetary system in terms of uniform circular motion. Ptolemy's abandonment of the principle of uniform circular motion was glaringly conspicuous already in ancient times, and the idea to reinstate it is so natural that it can hardly fail to suggest itself to any serious astronomer familiar with the classical astronomical tradition. Copernicus makes his dislike of the equant known immediately at the very beginning of the Commentariolus:Ptolemy ... envisioned certain equant circles, on account of which it appeared that the planet never moves with uniform velocity.... Therefore a theory of this kind seemed neither perfect enough nor sufficiently in accordance with reason.... I often pondered whether perhaps a more reasonable model composed of circles could be found from which every apparent irregularity would follow while everything in itself moved uniformly, just as the principle of perfect motion requires.4Islamic astronomers felt similarly, but there is no reason to think that Copernicus inherited his view from them since the principle of uniform circular motion was the most unquestionable axiom of astronomy already in Antiquity. This principle is affirmed for example by Plato, Timaeus 34a, and Aristotle, De caelo n.6, where the possibility of acceleration and deceleration in the heavens is explicitly rejected. Ptolemy himself stresses the point no less strongly (though obviously his interpretation of it is different from that of Copernicus):It is our purpose to demonstrate for the five planets that all their apparent anomalies can be represented by uniform circular motions, since these are proper to the nature of divine beings, while disorder and non-uniformity are alien [to such beings].5Thus Copernicus's concern to eliminate the equant is a natural continuation of classical astronomy. It is based on very natural considerations that would undoubtedly have occurred to him even if he had never heard of Islamic astronomy.Ragep argues to the contrary that Copernicus's work is inexplicable unless it is seen as stemming from the Islamic tradition:What seems to be overlooked by those who advocate a reinvention by Copernicus and/or his contemporaries of the mathematical models previously used by Islamic astronomers is the lack of an historical context for those models within European astronomy. At the least, one would expect to find some tradition of criticism of Ptolemy in Europe in which those models would make sense. But in fact this is not the case. Copernicus's statement of his dissatisfaction with Ptolemaic astronomy ... had no precedent in Europe but did have a continuous five-hundred-year precedent in the Islamic world.6But why it is so surprising that the same person who raises the criticisms of Ptolemy also works out an alternative? On the contrary, this seems to make perfect sense. …