CELESTIAL MOVERS IN MEDIEVAL PHYSICS 189 



mover of the celestial bodies is not a soul, then it is in no way 

 moved per accidens. This immediate mover could be God Him- 

 self or an angel. And if the number of angels is greater than 

 Aristotle conceded, then it is impossible to demonstrate that 

 God is the immediate mover of the heavens. This is precisely 

 the difficulty envisaged in St. Thomas' reply to the fifth ques- 

 tion: assuming that God is not the immediate mover, then it 

 is indeed demonstrated that an angel is the mover. This as- 

 sumption, however, cannot be made on philosophical, much 

 less on physical grounds. This is not to say that Aristotle failed 

 to prove the existence of God in Meta^physics XII. Quite the 

 contrary. St. Thomas was convinced that Aristotle perceived 

 that other mode of becoming yer influentiam essendi, whereby 

 every spiritual substance is necessarily dependent on the first 

 cause of being. It is this other mode of " being moved " that 

 St. Thomas sees in Aristotle's conception of the conjoined 

 mover of the first heaven."^ It is the totality of movers which 

 are in some true sense moved that validates the Aristotelian 

 argument for St. Thomas. " Hence, unless the celestial bodies 

 are moved immediately by God, they must either be animated 

 and moved by their proper souls or be moved by angels, quod 

 melius dicitur." 



Concluding his reply to the fifth question, St. Thomas notes 

 that there are some philosophers who would have God move the 

 first heaven by means of its anima propria, and the other 

 heavens by means of intelligences and souls. St. Thomas' 

 own view is that God directs the universe through a hierarchy 

 of angels, only the lower of which directly move the celestial 

 bodies. 



The view of St. Thomas is openly defended in the anonymous 

 Quaestio de viotoribus corporum caelestium, a work formerly 

 attributed to St. Thomas and still published among his works .^°' 



"*For example, In XII Metaph., lect. 7, nn. 2519-2522; lect. 8, nn. 2539-2543; 

 In II De caelo, lect. 18, n. 6. 



"^ Opera Omnia (Parma: Fiaccadori, 1869) , XXIV, pp. 217a-219b. This treatise 

 was first published by Thomas Boninsegnius, O. P., in his edition of the Summa 

 with Cajetan's commentary (Venice: apud Juntas) in 1588. The first folio an- 



