XI. Who, therefore, endued with intellect will doubt that a thing of this kind is not immortal, to which indestructible life is present from itself? For how is it possible it should perish, since it is not adventitious, and is not possessed in the same way as heat is present with fire ? I do not mean by this, that heat is adventitious to fire, but that it is so to the subject matter of fire, though it is not to fire itself. For through this fire is dissolved. Soul, however, does not possess life in such a way, as that matter is the subject of it, but life acceding, demonstrates the presence of soul. For either life is essence, and is an essence of such a kind as to live from itself, which is soul, the object of our investigation, and this they acknowledge to be immortal; or they must analyze it as a composite. This, also, they must analyze, till they arrive at that which is immortal, and moved from itself, and to which it is not lawful to receive the destiny of death. Or if they say that life is a passion adventitious to matter, they are compelled to acknowledge that nature to be immortal from which this passion was imparted to matter, and which is incapable of receiving the contrary to that which it imparts. For it is one nature living in energy.