I have thus shown the various classes of bodies as they are diversified by
their forms and combinations and changes into one another, and now I must
endeavour to set forth their affections and the causes of them. In the first
place, the bodies which I have been describing are necessarily objects of
sense. But we have not yet considered the origin of flesh, or what belongs to
flesh, or of that part of the soul which is mortal. And these things cannot be
adequately explained without also explaining the affections which are
concerned with sensation, nor the latter without the former: and yet to
explain them together is hardly possible; for which reason we must assume
first one or the other and afterwards examine the nature of our hypothesis. In
order, then, that the affections may follow regularly after the elements, let
us presuppose the existence of body and soul.