THE MEANING OF NATURE 261 



substantial form. As such, it is nature insofar as it was a prin- 

 ciple in the generation of the thing of which it is the soul and 

 also insofar as it is the principle of movements, such as falling, 

 that are natural to mobile beings already constituted. As soul, 

 in what is proper to it, it is a principle as well of the vegetative 

 operations. These, it is true, are still movements in the strict 

 sense, involving activity, passivity and alteration, all in the 

 strict sense. However, they are movements in which the 

 living being properly moves itself. The soul, unlike any mere 

 substantial form, constitutes the being as an agent with re- 

 spect to itself. It is still nature, insofar as it is a principle of 

 being moved, intrinsic to the moving being. However as an 

 active potency, it is a principle of moving rather than of being 

 moved, and of moving another as such ^° — in fact, the living 

 being moves itself only inasmuch as one part moves another 

 part. Thus as an active, motive principle, it has something 

 different from and more than mere nature. 



Then, a more perfect soul, the sentient, is capable not only 

 of these operations but of sense perception as well, which con- 

 sidered in itself, is not movement in the strict sense, but an 

 operation that is an actus perfecti.^^ It is movement in some 

 sense, however, " a sort of alteration," as Aristotle calls it, for 

 it involves a transition from potency to act. If the sentient soul 

 is considered to be nature insofar as it is a principle of move- 

 ment in a secondary sense, in this respect it can only be nature 

 according to an extended meaning. On the other hand, sensa- 

 tion involves movement in the strict sense, insofar as it re- 

 quires a corporeal organ; and it can result in movement in the 

 strict sense, since it can arouse the passions which involve 

 bodily modifications and at times also give rise to locomotion. 

 Because all these movements are proper to the sentient soul 

 as such, it too is properly termed nature. 



'"Aristotle, Metaph., V, 12, 1019al5 et sqq.; St. Thomas comments: "An active 

 principle of movement must be in something other than that which is moved." {hi 

 V Metaph., lect. 14, n. 955.) 



'^Aristotle, De Anima, III, 7, 431a6 et sqq.; St. Thomas, In III De Anima, lect. 

 12, n. 766. Cf. also, De Anima, II, 5; St. Thomas, In II De Anima,, lect. 10 & 11. 



