ORIGINS OF THE PROBLEM OF UNITY OF FORM 133 



Avicenna's treatment more systematically, provided the School- 

 men with the main elements of the problem by asserting un- 

 ambiguously (i) that the vegetative, the sensitive and the 

 rational, though three distinct substances when taken sepa- 

 rately, are one simple substance when united; (ii) that the 

 higher principle includes the lower, which is only virtually 

 present when the higher supervenes; (iii) that whatever per- 

 fection is superadded to an already constituted being does not 

 impart specific being, but merely accidental being; and conse- 

 quently (iv) that the vegetative, the sensitive and the rational 

 are in man not three distinct substances, but powers. The 

 formulation, the arguments and similies set forth by Gundis- 

 salinus will become a common patrimony and will be continu- 

 ally used in more or less refined fashion by successive genera- 

 tions of masters. Some confusion as to the unity of soul or sub- 

 stance will linger for a time, but soon philosophers and theo- 

 logians will accurately distinguish between the question of the 

 unity of soul and the unity of substance or form. 



Turning our attention now to the pluralist theory, Aquinas ^^ 

 traced its source remotely to Plato and proximately to Avice- 

 bron (Ibn Gebirol) . Both systems issue from the same root, 

 both present as reality what is a mere distinction of the mind, 

 and one is the sequel of the other.^^ The pluralist theory, in 

 fact, follows logically from Platonic presuppositions. Plato 

 holds that there are several souls in a body, distinct according 

 to different organs and their various vital actions, such as the 

 nutritive in the liver, the concupiscible in the heart, and the 

 knowing in the brain. ^^ Furthermore, he maintains that the 

 human soul is united to the body not as form to matter, but 

 merely as mover to the moved, just like a sailor in a boat; and 

 again, that man is not composed of soul and body, but that 



^' St. Thomas, De spiritualihus creaturis, a. 3 (ed. Keeler, pp. 40-41) . 



^^ St. Thomas, Summa theoL, I, q. 76, aa. 3-4. " Et haec positio [Avicebron's], 

 quamvis videatur discordare a prima [Plato's], tamen secundum veritatem rei 

 cum ea concordat, et est sequela eius." De spirit, creat., loc. cit. 



^" Cf. St. Thomas, QQ. dis-p. de anima, a. 11: " Plato posuit diversas animas esse 

 in corpore; et hoc quidem consequens erat suis principiis." Also Summa theoL, I, 

 q. 76, a. 3. 



