 it seems that what we call not this, but that-en—for example, we call the box not wood, but wooden, nor do we call the wood earth, but earthen, and again earth, if it is this way, we do not call something else, but that-en—that is always potentially without qualification the next thing…But if there is something primary, which is no longer called that-en with respect to something else, this is prime matter. For example, if earth is airy, and air is not fire but firey, fire is prime matter, being a this. (1049a18–22…24–27) 