We should say a little more about the nature of mixture and change. As in many areas, Galen here tries to avoid intricate and undecidable metaphysical debates, while insisting on certain fixed points. One of the latter, as we have seen, is the four-element theory; another is the understanding of the physical world as a continuum, rather than as some set of bodies interspersed with void. As to the nature of the change that takes place in mixture: krasis must be understood to be a process in which the elements involved undergo some fundamental change; it is not a mere placing alongside each other of tiny quanta of different substances (as might happen in mixing two powders), whereby those substances themselves remain in principle capable of being separated, and retain their original properties. What happens, rather, is that a new substance arises with distinct properties, and the smallest imaginable quantum of this new substance would have those distinct properties, not those of the elements from which it was mixed.