214 W. A. WALLACE 



" a twofold accidentality to be noted in such motions, both 

 coming from whatever restrains or impedes bodies of this type; 

 one is an [accidental] potency by which it ' happens ' that they 

 can be moved; the other by which it ' happens ' that they are 

 moved successively, for otherwise, once all impediments are 

 removed, they would move instantly." ^^ Unfortunately Theo- 

 doric does not elaborate this very interesting observation, but 

 immediately adds the colophon and explicit, bringing his opus- 

 culum on the elements to rather an abrupt close. 



As to the precise mechanics favored by Theodoric for ex- 

 plaining the quantitative aspects of gravitational motion, one 

 can only adduce indirect evidence. Two views were current 

 among his contemporaries, one deriving from Averroes, which 

 would have the velocity of fall directly proportional to the 

 motive force and inversely proportional to the resistance of 

 the medium, the other deriving from Avempace and having 

 the velocity proportional to the difference between the motive 

 force and the resistance of the medium.*'* Theodoric seems to 



"' Cap. 47, M 18vb-19ra, T 185v, U 147rb: Sed ex hoc frustium uititur quis recti- 

 ficai'e errorem suum quo asserit huiusmodi moveri a generante eo modo qui improba- 

 tus est, scilicet, in habeiido formam seu speciem a generante. Aliud est reducere aliquid 

 in aliud sicut in causam essencialem, secundum consideracionem primi philosophi, 

 qui considerat rerum essencias secundum racionem suarum quidditatum; aliud est 

 querere de alicuius principio motivo, secundum quod physicus liabet considerare. 

 Unde aliquid potest reduci in causam propriam secundum quod primus pliilosophus 

 considerat, quod non potest reduci in ipsam ita quod ipsa sit principium motivum. 

 Et sic se habet in proposito quantum ad motus gravium et levium, ut patet ex 

 prehabitis. Unde generans non est principium motivum nisi quando actu movet per 

 generacionem rei. Est autem principium causale [tale U] eciam postquam generavit, 

 sed removens prohibens est principium motus, attamen per accidens inquantum 

 physicus considerat de motu, videlicet, inquantum motus. Et secundum istum 

 modum cucurrit questio proposita de motibus gravium et levium, et negatur quod 

 moveantur a generante. Sed est hie advertenda duplex accidentalitas in motibus 

 istorum, et utraque est a prohibente seu impediente huiusmodi mobilia. Una est 

 secundum potenciam ad motum qua accidit eis moveri, alia est qua accidit eis 

 successive moveri; alias enim, remoto omni impedimento, mutarentur in instanti, 

 ut predictum est. Hec igitur sufficiant de dementis mquantum sunt partes mundi; 

 alibi enim de ipsis tractatum est inquantum sunt miscibiiia et partes mixti. 

 Explicit. . . . 



"^For details, see Maier, " Platonische Einflus!.-! in der scholastischen Me- 

 chanik.'," Studien V, pp. 237-285. 



