154 JAMES A. WEISHEIPL 



In the first place, astronomy was classified with optics, 

 mechanics, harmonics and other scientiae mediae between the 

 sciences of pure mathematics and natural science.^ As a sci- 

 ence intermediate between mathematics and physics, astronomy 

 was considered from three points of view. First, it was con- 

 sidered in relation to the higher science of mathematics, to 

 which it is subalternated and on which it depends for its scien- 

 tific validity. Astronomy, it was said, accepts as established 

 all the conclusions of geometry and applies them to the known 

 measurements of celestial phenomena. In this consideration, 

 astronomy and the other scientiae mediae " have a closer 

 affinity to mathematics, because what is physical in their con- 

 sideration functions as something material, while what is 

 mathematical functions as something formal." ^ Intelligibility 

 in every science was taken as derived from the principles, the 

 formal element, as contrasted to the material element which is 

 the conclusion, or fact now understood scientifically.^" We 

 know that mathematical astronomy did not begin until Eu- 

 doxus of Cnidos accepted the challenge from Plato " to find out 

 what are the uniform and ordered movements by the assump- 

 tion of which the phenomena in relation to the movements of 

 the planets can be saved." ^^ The obviously irregular motions 

 in the heavens, tabulated for centuries before Plato, could not 

 be made intelligible except by reducing them, at least in theory, 

 to perfectly regular movements of geometric spheres. In other 

 words, astronomy was taken formally to be a mathematical 

 type of knowledge, extending to measurable quantities of 

 celestial phenomena, such as size, distance, shape, position and 

 velocity. 



Considered in its own right, astronomy was presented as a 

 true speculative science, demonstrative within its own limits. 

 Unless there be some true demonstrations in astronomy, true 



* St. Thomas, In I Post. Anal, lect. 1, n. 3; In II Phys., lect. 3, n. 8; In Boeth. 

 de Trin., q. 5, a. 3 ad 5-7; Sum. theol., I-II, q. 35, a. 8; II-II, q. 9, a. 2 ad 3. 



* In Boeth. de Trin., q. 5, a. 3 ad 6; Sum. theol, II-II, q. 9, a. 2 ad 3. 



"/n / Post. And., lect. 41, n. 11; Sum. theol, II-II, q. 1, a. 1; q. 9, a. 2 ad 3. 

 " Simplicius, De caclo, ed. Heiberg (Comm. in Arist. Graeca, VII) , p. 488, 18-24. 



