GRAVITATIONAL MOTION 207 



of Aristotle in Theodoric's time, being in fact proposed by 

 various of his contemporaries, including Siger of Brabant, 

 Godfrey of Fontaines, John Peter Olivi and Duns Scotus.*^ 

 But our German Dominican does not regard this explanation 

 as consistent with the remainder of Aristotelian doctrine, and 

 gives seven arguments why it should be rejected. 



The first is drawn from the processive motion of animals, to 

 which Theodoric would apply a similar analysis to the one 

 here invoked for the local motion of heavy objects, insofar as 

 it too derives from a natural form. This would result in an 

 animal's locomotion being caused by its generator (i. e., its 

 parent) , which Theodoric calls " absurd." *^ The second argu- 

 ment is drawn from a similar application to the heavenly bodies: 

 Theodoric merely points out that all metaphysicians agree that 

 the latter are moved by another, but no one claims that they 

 are moved by their generator .^^ His third argument is for those 

 who are dissatisfied with the argument from animal locomotion, 

 and is concerned with the motion of the heart and arteries: 

 these are clearly vital motions, and as such must come from 

 within — therefore they cannot proceed from the generator.^* 



Should one reply to these arguments, moreover, that they 

 concern living things whose motions proceed from an active 

 intrinsic principle, while falling bodies (as such) are non-living 

 and only have a passive principle of motion within them, 

 Theodoric will concede the objection. But then his fourth argu- 



moventur a generante, eo quod habent formam que est principium motus a gene- 

 rante, a quo sicut habent huiusmodi formam et speciem, sic habent omnia naturalia 

 accidencia que consequuntur speciem, quorum unum est naturahs motus secundum 

 locum. . . . 



*^ For details, see Maier, Studien III, pp. 158-164. This was also the teaching 

 of St. Thomas Aquinas (In II Phys., lect. 1, n. 4; In III De caelo, lect. 7, nn. 8-9; 

 In V Metaph., lect. 14, n. 955) , but there are subtleties in Thomas' exposition that 

 have been commonly overlooked by historians. For a clear presentation of the 

 original Thomistic doctrine and its relation to Arab and late scholastic thought, 

 see James A. Weisheipl, O. P., Nature and Gravitation, (River Forest, 1955) , pp. 

 19-32. 



" Cap. 29, M 17ra, T 184r, U 144vb. 



" Cap. 30, M 17ra, T 184r, U 144vb. 



" Cap. 31, M 17ra, T 184r, U 144vb-145ra. 



