CELESTIAL MOVERS IN MEDIEVAL PHYSICS 157 



[demonstratively] adequate, since some other theory might explain 

 them.^* 



The tentative and hypothetical character of astronomical 

 theories was commonly recognized from the thirteenth century 

 onward, that is, after the acceptance of both Aristotle and 

 Ptolemy in Latin translation. The homocentric hypotheses 

 of Eudoxus and Callippus were taught in the faculty of arts 

 together with the Ptolemaic hypotheses of epicycles and eccen- 

 trics. The schoolmen frequently discussed the preferability of 

 one over the other in their commentaries on Aristotle. 



This brings us to the second peculiar characteristic of astron- 

 omy recognized in the Middle Ages, namely that mathematical 

 astronomy was ordained to the discovery of true physical causes 

 in nature. The mathematical character of astronomy was 

 clearly evident to the schoolmen. But as mathematical, it 

 abstracted from all questions of efficient, final and material 

 causality; its concern was with the quantitative formalities of 

 celestial phenomena related functionally to assumed mathe- 

 matical principles. [Astronomi] non considerant motum caeles- 

 tium secundum principia Tnotus, sed potius secundam numerum 

 et mensuram quantitatis suae.^^ This being the case, one might 

 have expected such an abstract science to be an end in itself, 

 a purely speculative science sought for its own sake. In actual 

 fact, however, this was not the view of Albertus Magnus, 

 Thomas Aquinas or Robert Kilwardby. These three men, it is 

 true, did not consider the functional use of astronomy in the 

 same way, but they did consider astronomy to have a func- 

 tional use in discovering real physical causes beyond quantity. 



In the Second Book of the Physics Aristotle had raised the 

 problem concerning the relation between the mathematical 

 sciences and natural science.-" Taking the case of astronomy, 

 Aristotle posed the dialectic: astronomy is obviously a part of 

 mathematics, but it is also a part of natural science since it 



^* St. Thomas, Sum. theoL, I, q. 32, a. I ad 2. 



" St. Albert, Lib. XI Metaph., tr. 11, cap. 10, ed. Borgnet (Paris: Vives, 1890- 

 1899), VI, 628a. 

 '" Arist., Phys. II, c. 2, 193b22-194al2. 



