Book 8
6
No one of them, nor the combination of any two of them, is substance, but nevertheless each one of them contains something analogous to substance. And just as in the case of substances that which is predicated of the matter is the actuality itself, so in the other kinds of definition it is the nearest approximation to actuality. E.g., if we have to define a threshold, we shall call it a piece of wood or stone placed in such-and-such a way; and we should define a house as bricks and timber arranged in such-and-such a way;
7
or again in some cases there is the final cause as well. And if we are defining ice, we shall describe it as water congealed or condensed in such-and-such a way; and a harmony is such-and-such a combination of high and low; and similarly in the other cases.
7
From this it is evident that the actuality or formula is different in the case of different matter; for in some cases it is a combination, in others a mixture, and in others some other of the modes which we have described.
8
Hence in defining the nature of a house, those who describe it as stones, bricks and wood, describe the potential house, since these things are its matter; those who describe it as a receptacle for containing goods and bodies, or something else to the same effect, describe its actuality; but those who combine these two definitions describe the third kind of substance, that which is composed of matter and form.
9
For it would seem that the formula which involves the differentiae is that of the form and the actuality, while that which involves the constituent parts is rather that of the matter. The same is true of the kind of definitions which ArchytasA celebrated Pythagorean, contemporary with Plato. used to accept; for they are definitions of the combined matter and form. E.g., what is windlessness? Stillness in a large extent of air; for the air is the matter, and the stillness is the actuality and substance.
