Plutarch, De Stoicorum repugnantiis
Goodwin, Ed.

He says that the air is by nature dark, and uses this [p. 470] as an argument of its being also the first cold; for that its darkness is opposite to the brightness, and its coldness to the heat of fire. Moving this in his First Book of Natural Questions, he again in his treatise of Habits says, that habits are nothing else but airs; for bodies are contained by these, and the cause that every one of the bodies contained in any habit is such as it is, is the containing air, which they call in iron hardness, in stone solidness, in silver whiteness. These words have in them much absurdity and contradiction. For if the air remains such as it is of its own nature, how comes black, in that which is not white, to be made whiteness; and soft, in that which is not hard, to be made hardness; and rare, in that which is not thick, to be made thickness? But if, being mixed with these, it is altered and made like to them, how is it a habit or power or cause of these things by which it is subdued? For such a change, by which it loses its own qualities, is the property of a patient, not of an agent, and not of a thing containing, but of a thing languishing. Yet they everywhere affirm, that matter, being of its own nature idle and motionless, is subjected to qualities, and that the qualities are spirits, which, being also aerial tensions, give a form and figure to every part of matter to which they adhere. These things they cannot rationally say, supposing the air to be such as they affirm it. For if it is a habit and tension, it will assimilate every body to itself, so that it shall be black and soft. But if by the mixture with these things it receives forms contrary to those it has, it will be in some sort the matter, and not the cause or power of matter.