CELESTIAL MOVERS IN MEDIEVAL PHYSICS 167 



only as the cause of motion, specifically as the cause of celestial 

 motion. 



St. Albert accepted the order of celestial spheres commonly 

 taught by the Arabian astronomers. The spheres were con- 

 sidered generically to be ten in number: the primum mobile 

 causing diurnal movement of the whole universe, the sphere of 

 fixed stars, the spheres of Saturn, Jupiter, Mars, the Sun, 

 Venus, Mercury, the Moon, and the terrestrial sphere of active 

 and passive elements.*^ It was well understood by all that each 

 so-called sphere was subject to many distinct motions, each of 

 which required some kind of mover. But it was simpler to 

 talk in terms of the clearly visible planets, the fixed stars and 

 the unseen cause of diurnal motion, than in terms of the precise 

 number of celestial motions postulated to save the appearances 

 of each planet. Similarly, it was understood among the better 

 informed that the notion of " sphere " was postulated to 

 regularize the errant motions of the planets and to give intel- 

 ligibility to their complicated movements. Those spheres were 

 no more " solid," contrary to some modern interpretations, 

 than the familiar sphere of terrestrial change. 



In the view of Avicenna each sphere was moved and ruled 

 by a separated substance, whatever may have been the number 

 of distinct movements required for each planet. It is within 

 this context that St. Albert discusses the problem of celestial 

 movers. But Avicenna further identified those intelligences and 

 the proximate mover {anima nobilis) with angels .°° St. Albert, 

 as has already been noted, was unwilling to identify the sepa- 

 rated substances of the philosophers with the angels of Sacred 

 Scripture. Further, the tenth intelligence for Avicenna was the 

 intellectus agens hominum, which ruled the terrestrial realm of 

 mutable substances by infusing forms from without. This dator 

 formarum was invoked by Avicenna to explain the apparent 

 generation of new substances in the world of nature. St. Albert 



*' St. Albert, Problemata determinata, q. 2, ed. cit., p. 324; see ibid., note 9. 



'° An excellent discussion of this has been given by Henry Corbin in his 

 Avicenna and the Visionary Recital, trans, by W. R. Trask (New York: Pan- 

 theon, Bollingen Series 66, 1960), pp. 46-122. 



