THE MEANING OF NATURE' 253 



In short, it is as a principle of movement accepted in the 

 strict sense ^ (movement involving a material substratum) 

 that nature is identified severally with matter and with form. 

 Clearly it is not to be taken either as essence, the root of 

 spiritual operations, or as essence without reference to move- 

 ment in any sense.^° Nature, in fact, is something proper to 

 material beings, since all natural beings are mobile beings and 

 all mobile beings are material beings. In this meaning of 

 nature, it might be added, we find the basis for distinguishing 

 between philosophy of nature and metaphysics as to mobility 

 and immobility, materiality and pure inmiateriality. 



n 



Nature as Both an Active and a Passive Principle 



For a fuller understanding of nature, the various ways in 

 which it is both an active and a passive principle must be 

 examined. It has already been indicated that nature can be 

 both active and passive. Does this division coincide exactly 

 with the division of nature into matter and form? This might 

 seem to be the case since in the commentaries of St. Thomas 

 the passive principle is usually associated with matter or what 

 is material (piincipium fasdvum et materiale) and the active 

 with form or what is formal {princvpium activum et formale) }'^ 

 At times, however, St. Thomas identifies the form with a pas- 

 sive principle as he often does when he speaks of the intrinsic 

 principle of falling bodies.^" We might be inclined to dismiss 

 the difiiculty with the distinction that when it is not a question 

 of living things both form and matter must be included under 



' This sense is not the strictest since it includes generation and corruption, as 

 well as movement taken in the strictest sense involving two positive terms (cf. 

 Arist., Physics, Y, ch. 1). It is a strict sense in that it excludes operations such 

 as thought. 



^° It could be taken as essence considered as a composite principle of accidental 

 movements (strict sense). For example, the composite nature of a living being, 

 including both matter and form, is a principle of growing, more adequate than 

 either matter or form taken alone. 



" Cf. In VII Metaph., lect. 8, n. 1442Z. 



^^ Cf., e. g., In II Phys., lect. 1, n. 4. 



