188 JAMES A. WEISHEIPL 



matter in generable substances, the celestial body must be 

 moved by another, by one in continual contact with it. Conse- 

 quently celestial bodies have " nature " only in the sense of a 

 passive (material) principle, which means the natural aptitude 

 to be moved by another. Hence "the motion of a celestial 

 body, as far as its active principle is concerned, is not natural, 

 but voluntary and intellectual; however, in relation to its pas- 

 sive principle, the motion is natural, for a celestial body has a 

 natural aptitude for such motion." ^°- In this matter, notes St. 

 Thomas, it makes no difference whether we conceive the celes- 

 tial bodies to be moved by intellectual substances conjoined 

 to the body after the manner of a soul or by one entirely dis- 

 tinct like an angel. Non auteTn esset via solvendi, si moverentur 

 -per solum naturae impetuTn, sicut corpora gravia et levia^°^ 



It is true that for St. Thomas celestial bodies can have only 

 a passive nature whether the mover be a conjoined soul as 

 Aristotle wished or a separated angel, as he himself believed. 

 Nevertheless in establishing the existence of God along Aris- 

 totle's lines, it does make a difference. St. Thomas, as St. 

 Albert before him, was well aware that the First Mover of the 

 Physics was for Aristotle identical with the First Being of 

 Metaphysics XII. That is to say, St. Thomas knew St. Albert's 

 interpretation to be correct. However, there is a serious diffi- 

 culty. If the celestial movers are not souls, but angels, as St. 

 Thomas himself held with the Sancti, then Aristotle's argument 

 is not conclusive. A soul conjoined to the sphere is necessarily 

 moved per accidens, that is, concomitantly with the sphere. 

 Since this kind of mover is insufficient to account for the pri- 

 mary source of physical motion, one can validly conclude to the 

 existence of an intelligence which is entirely separated from 

 matter. And if one erroneously limits the number of spiritual 

 substances to the number of celestial movements, then the sepa- 

 rated intelligence moving the first animated sphere (primum 

 caelum) must be God. On the other hand, if the immediate 



^°'^ Sum. cont. gent., Ill, c. 23, § 8. Also In II Phys., lect. 1, n. 4; in II De caelo, 

 lect. 3, n. 2, and lect. 18, n. 1; De pot., q. 5, a. 5 ad 12. 

 ^°'' St. Thomas In II De caelo, lect. 18, n. 1. 



