CELESTIAL MOVERS IN MEDIEVAL PHYSICS 187 



end, therefore, is already within the intentionality of nature as 

 form. Once nature has attained the end, it must rest in its 

 acquisition, since it is its good. Physically there is no need for 

 any " conjoined mover " to account for this motion downward 

 or upward. Nature itself spontaneously moves toward the end 

 which is its goal. " There is in heavy and light bodies a formal 

 principle of its motion, because, just as other accidents pro- 

 ceed from the substantial form, so does place and, consequently, 

 movement toward place; not however that the natural form is a 

 mover {motor) , but the mover is the generator which begot 

 such a form upon which this motion follows." "° Therefore 

 nature as an active principle is always ordained to rest in the 

 possession of some good proper to itself. 



For St. Thomas the profound difference between celestial 

 and terrestrial phenomena lay in the motions. The heavens 

 move continuously in time, aiming at no rest or possession of 

 a goal. Whether the heavens are eternal or created in time is 

 not relevant to the question. Likewise it makes no difference 

 whether the celestial bodies in motion are real spheres or inde- 

 pendent planets; in either case the motion is always ordered 

 to further motion. Clearly these motions cannot be striving for 

 a rest as yet unattained, since such a rest would be disastrous 

 for the celestial body and no nature can desire its own destruc- 

 tion as a good. Nor can it be said that the purpose of such 

 motion is motion itself. Motion by its very nature is a tending, 

 a continual otherness; it has within its very nature a deformity 

 which is incapable of being the final cause of any natural agent. 

 " Therefore it is impossible that nature intend motion for the 

 sake of motion." "^ Now for St. Thomas, if there is no intrinsic 

 end attainable by a body in motion, then that motion cannot 

 have sprung spontaneously from nature as form. Like the 



100 g(. Thomas, In II Phys., led. 1, n. 4. Also In I De caelo, lect. 18, n. 1; 

 II, lect. 2, n. 6; III, lect. 7, nn. 5-9; In II Phys., lect. 5, n. 5; IV, lect. 12, n. 9; 

 VIII, lect. 8, nn. 5-7; Sum. cont. gent.. Ill, cc. 82, 84; De pot., q. 5, a. 5. 



^"^ " Impossible est igitur quod natura intendat motum propter seipsum." Sum. 

 cont. gent., Ill, c. 23, § 6. Also De pot., q. 5, a. 5: " impossible est quod aliqua 

 natura inclinet ad motum secundum se ipsum." 



