THE MEANING OF NATURE 251 



them a source of movement or change in respect of place or 

 size or some quality or other, whereas products of art have no 

 inner tendency to change, except insofar as they are made of a 

 natural substance. From this he concludes that nature is this 

 pnnciple or cause of being moved and being at rest in that in 

 which it is, and he adds by way of precision, iri which it is pri- 

 marily, in virtue of itself and not accidentally. 



This definition, it will be noticed, is the third meaning given 

 in the Metaphysics, but with certain additions. Nature is de- 

 fined here not merely as a principle but as a cause as well. 

 According to St. Thomas, this is to indicate that nature may be 

 either a passive source (principle) or an active source (cause) . 

 These two senses of nature will constitute the subject for the 

 second part of this article; and in the third part we shall con- 

 sider the word primarily. The words in virtue of itself and not 

 accidentally, we may note here, are meant to exclude such 

 intrinsic principles as the art of medicine in virtue of which a 

 doctor cures himself. The movement of being cured belongs 

 to the man per se as a patient, not as a doctor; it is only acci- 

 dentally that the doctor is also the patient. 



After defining nature, Aristotle proceeds to make certain 

 distinctions concerning the use of the word: those things are 

 said " to have a nature " which have this principle of movement 

 and they are substances; and both the subject which has its 

 being from nature and the accidents which are caused by this 

 nature are said to be natural or according to nature. 



Nature is then identified, as it is in the Metaphysics, with 

 " the first material substratum of all things which have in them- 

 selves a principle of movement and change "; and then with 

 the form of these tilings, insofar as " what is potentially flesh or 

 bone does not have its nature until it receives the form by 

 which we define what flesh or bone is." Both matter and fonn 

 are nature but each in a different way, and unequally, since 

 form is nature even more than matter is: " for a thing is more 

 properly said to be what it is when it is in act than when it 

 exists only potentially," 



In the Physics, accordingly, nature is seen to be the form 



