22 R. Attend therefore to the few things that remain. A. Bring forth whatever you have, if only it be such as I can understand, and I will willingly agree. R. We do not forget, that to say that anything is in anything, is capable of a double sense. It may mean that it is so in such a sense as that it can also be disjoined and be elsewhere, as this wood in this place, or the sun in the East. Or it may mean anything is so in a subject, that it cannot be separated from it, as in this wood the shape and visible appearance, as in the sun the light, as in fire heat, as in the mind discipline, and such like.
Or seems it otherwise to you? A. These distinctions are indeed most thoroughly familiar to us, and from early youth most studiously made an element of thought; wherefore, if asked about these, I must needs grant the position at once. R. But do you not concede that if the subject do not abide, that which is in the subject cannot inseparably abide? A. This also I see necessary: for, the subject remaining, that which is in the subject may possibly not remain, as any one with a little thought can perceive.
Since the color of this body of mine may, by reason of health or age, suffer change, though the body has not yet perished. And this is not equally true of all things, but of those whose coexistence with the subject is not necessary to the existence of the subject. For it is not necessary that this wall, in order to be a wall, should be of this color, which we see in it; for even if, by some chance, it should become black or white, or should undergo some other change of color, it would nevertheless remain a wall and be so called. But if fire were without heat, it will not even be fire; nor can we talk of snow except as being white.
Source: Soliloquies (New Advent)