softness, and the rest of them: all of which are derived from the
hot and the cold and the mixture of their motions. But no one would go
as far as to consider them sufficient in the case of the
non-homogeneous parts (like the head, the hand, or the foot) which
these homogeneous parts go to make up. Cold and heat and their
motion would be admitted to account for the formation of copper or
silver, but not for that of a saw, a bowl, or a box. So here, save
that in the examples given the cause is art, but in the nonhomogeneous
bodies nature or some other cause.
Since, then, we know to what element each of the homogeneous
bodies belongs, we must now find the definition of each of them, the
answer, that is, to the question, 'what is' flesh, semen, and the
rest? For we know the cause of a thing and its definition when we know
the material or the formal or, better, both the material and the
formal conditions of its generation and destruction, and the efficient
cause of it.
After the homogeneous bodies have been explained we must consider
the non-homogeneous too, and lastly the bodies made up of these,
such as man, plants, and the rest.