Book 5
7
That which comprises both of these exists by nature; e.g. animals and their parts. And nature is both the primary matter (and this in two senses: either primary in relation to the thing, or primary in general; e.g., in bronze articles the primary matter in relation to those articles is bronze, but in general it is perhaps water—that is if all things which can be melted are water) and the form or essence, i.e. the end of the process, of generation. Indeed from this sense of nature, by an extension of meaning, every essence in general is called nature, because the nature of anything is a kind of essence.
8
From what has been said, then, the primary and proper sense of nature is the essence of those things which contain in themselves as such a source of motion; for the matter is called nature because it is capable of receiving the nature, and the processes of generation and growth are called nature because they are motions derived from it. And nature in this sense is the source of motion in natural objects, which is somehow inherent in them, either potentially or actually.
