126 DANIEL A. CALLUS 



Giles of Rome,* in which Aristotle and Avicenna are made re- 

 sponsible for the thesis: Quod in quolihet composito sit una 

 forma substantialis tantum. The author, who is on the whole 

 familiar with the facts, argues that the unity thesis is a logical 

 inference of the Aristotelian doctrine on change and movement. 

 For, since the coming-to-be of a thing never takes place without 

 the passing-away of another, and one substantial form is never 

 introduced unless the one which preceded it is expelled — seeing 

 that the matter of all things material is the same — it follows 

 that there are no more substantial forms in one composite than 

 there are in another. Nay if one stresses this point rightly, it 

 seems necessary to maintain that there is in all compounds one 

 substantial form only: and indeed this appears to be the Phi- 

 losopher's position. In fact, in the Metaphysics, Book VII, in 

 the chapter ' On the unity of definition,' he states that the 

 attributes in the definition are one, not because they are present 

 in one thing, but because they constitute one nature, one thing. 

 If he means one thing composed of many forms, this view may 

 be tolerated, but if he means one simple nature and that in the 

 concrete thing there is one form only, then it is false .^ 



Doubtless in the Aristotelian system there can be no room for 

 the theory of plurality of forms. St. Thomas more than once 

 pointed out that haec positio (plurality of forms) secundum 

 vera philosophiae principia quae consideravit Aristoteles est 



* Giles of Rome Errores Philosophorum, ed. J. Koch (Milwaukee: Marquette 

 Univ., 1944). 



^ Among Aristotle's errors: "11. Ulterius, quia per viam motus nunquam est 

 generatio unius, nisi sit corruptio alterius, et nunquam introducitur una forma 

 substantialis, nisi expellatur alia, cum eadem sit materia omnium habentium earn 

 (De gen. et corrup., I. 3, 319 a 33-b 5; c. 5, 320 b 12-14), sequitur ex hoc quod non 

 sint plures formae substantiales in uno composito quam in alio. Immo qui bene pro- 

 sequitur viam istam, videtur esse ponendum in omni composito unam formam sub- 

 stantialem tantum; et ista videtur via Philosophi. Unde VII° Metapliysicae, 

 capitulo ' De unitate diffinitionis,' vult partes diffinitionis non esse unum (Z. 12, 

 1037 b 22-27) , ' quia sunt in uno,' sed quia dicunt unam naturam. — Quod si intel- 

 ligit unam naturam compositam ex pluribus formis, posset tolerari; sed si intelligit 

 unam naturam simplicem, et quod sit in composito una forma tantum, falsum est." 

 Ibid., p. 8. And in the summa errorum: "11. Quod in quolibet composito sit una 

 forma substantialis tantum." p. 12. 



