CELESTIAL MOVERS IN MEDIEVAL PHYSICS 181 



movers for the heavens', but these are certainly not the angels 

 discussed by Catholics. Even assuming that God is not the 

 immediate mover of the heavens — which according to Kil- 

 wardby He is not — it is in no way proved that angels have to 

 be celestial movers (q. 5) . Unlike St. Albert, Kilwardby con- 

 ceives the physical universe as perfectly self-contained, per- 

 fectly " natural," having no need of immaterial agencies direct- 

 ing and moving the heavens. His is the closed world created 

 by God in the beginning with sufficient innate tendencies to 

 move rectilinearly and rotationally. 



This view was not original with Robert Kilwardby. Fr. 

 Daniel A. Callus has pointed out that this idea can be traced 

 to the earliest days of Aristotelianism in Oxford. Some sixty 

 years before Kilwardby's reply, John Blund gave as his con- 

 sidered opinion that the heavenly bodies are not moved by 

 souls, nor by intelligences, but by their own active nature 

 moving orbiculariter.^^ As is commonly known, this opinion 

 found favor among many in the fourteenth and fifteenth 

 century. 



Fr. Chenu saw in Kilwardby's view an anticipation of John 

 Buridan's famous suggestion about celestial motions, that an 

 impetus (given by God) is also found in the celestial spheres, 

 but one which cannot be diminished by resistance, since celes- 

 tial matter offers no resistance.®'^ In all terrestrial projectiles 

 impetus is diminished and overcome by nature resisting the 

 violent force. But in Aristotelian theory celestial bodies could 

 offer no resistance, since they had no weight or gravity; they 

 were considered completely passive, having " nature " only as 

 a passive principle of motion. Consequently Buridan's sug- 

 gestion of an initial impetus for celestial motion was a perfectly 

 obvious one; it presupposes Aristotle's doctrine of the pure 

 passivity of those bodies. In other words, it is precisely because 



** " Dicimus quod firmamentum movetur a natura, non ab anima, et alia super- 

 celestia." The full passage is published by Daniel A. Callus, O. P., " The Treatise 

 of John Blund On the Soul," in Autour d'Aristote (Louvain, 1955) , pp. 487-9. 



" Cf. Pierre Duhem, tltudes sur Leonard de Vind, III (Paris: Nobele, 1955) , 

 p. 42. 



