  As internal principles of moving and rest, natures stand in an exclusive relationship to the efficient or moving causes of the motions and rests they bring about: in some cases when Aristotle is not specifying the first moving cause, he can assert the identity of nature and moving cause. Accordingly, the soul of living beings will be identified as the substance (i.e., form) and the moving cause of the  organism whose soul it is.[8]   But the identification, even in this restricted sense, will need some further important qualifications, to which we will return in Section 5 below, on movers and unmoved movers.