On Prayer 27.8

Being (ousia) in the proper sense, according to those who say that the existence of incorporeal things is primary, is understood to belong to incorporeal things, which possess being firmly and neither admit addition nor suffer subtraction (for this belongs to bodies, in which growth and decay occur because they are in flux and need something that comes in to support and nourish them; if at any time more comes in than flows away, there is increase, and if less, decrease; and perhaps some things that receive nothing at all coming in are, so to speak, in unmixed decrease). But according to those who think that incorporeal existence is secondary and that of bodies primary, its definitions are these: being is either the primary matter of existing things, from which existing things come; or the matter of bodies, from which bodies come; or of things named, from which things named come; or the first substrate without quality; or that which underlies existing things; or that which receives all changes and alterations while itself unaltered in its own nature; or that which endures every alteration and change. According to these, being is in its own nature without quality and without shape, and does not even have a determined size, but lies ready for every quality like a prepared place. And by qualities, in their technical sense, they mean activities and productions in general, in which motions and states happen to exist; for they say that being in its own nature participates in none of these, but is always inseparable from one of them by being affected, and nonetheless is receptive of all the activities of the agent, as it acts and changes it; for the tension that is with it and has passed through all of it would be the cause of every quality and of the dispositions concerning it. And they say that it is changeable throughout and divisible throughout, and that every being can be mingled with every other, while remaining united.