186 JAMES A. WEISHEIPL 



celestial movers, then no learned man can doubt that all natural 

 motions of lower bodies are caused by the motion of celestial 

 bodies (q. 3) . Dionysius himself notes that the sun's rays 

 induce the generation of sensible bodies, generate life itself, 

 nurture, strengthen and perfect it. All of this is within the 

 power of angels. 



For some reason St. Thomas omitted to answer the fourth 

 question directly. It asks whether it is infallibly demonstrated 

 according to anyone that angels are the movers of celestial 

 bodies. In two earlier replies to the lector of Venice, St. Thomas 

 answered this very question in clear terms: 



The books of the philosophers abound with proofs for this, proofs, 

 which they consider demonstrations. It seems to me therefore that 

 it can be demonstrated that celestial bodies are moved by some 

 intellect, either by God immediately or by means of angels moving 

 them.®^ 



Consequently his reply to the fifth question comes as no sur- 

 prise. He categorically insists that if God does not move those 

 bodies immediately, then some other spiritual substance is 

 demonstrated as mover, either a celestial soul or a separated 

 angel. The fundamental reason for this assertion is stated 

 clearly: Quod autem corpora caelestia a sola natura sua move- 

 antur, sicut gravia et levia, est omnino impossibile.^^ In other 

 words, for St. Thomas it is absolutely impossible that circular 

 motion be explained by nature as an active (formal) principle 

 within celestial bodies. This view is directly opposed to the 

 position represented by Kilwardby. 



Throughout all his writings St. Thomas insisted on the essen- 

 tial difference between rectilinear motion and rotational motion. 

 Rectilinear motions, such as those of heavy and light bodies, 

 arise spontaneously from within bodies, from nature as an 

 active (formal) principle. Nature in this sense is predeter- 

 mined to a certain end and to the means of attaining it. The 



** St. Thomas, Resp. de art. XXXVI, a. 2; also Resp. de art. XXX, ad 4. 

 *' St. Thomas, Resp. ad Joan. Vercel., q. 5; cf. Sum. contra gent.. Ill, c. 23 per 

 totum. 



