Since, throughout all nature, there is a matter for each genus of entities (that which all belonging to that genus are in potentiality), and a something which is causative and constitutive from its making things what they are, as art impresses its forms upon matter, so those same distinctions must, of necessity, co-exist in the vital principle. Such also is the mind, from its faculty, on the one hand, of becoming all things, and, on the other, of creating all things, as if it were a virtuality like light; for light, in a certain sense, makes colours, being in potentiality, to become colours in reality; and the mind here meant is separate, impassive and homogeneous, being essentially an energizing influence.
That which acts is ever, in fact, more influential than that which is acted upon, as the causative principle is than the matter. Now, knowledge in activity is identical with the subject; but knowledge in potentiality pre-exists in the individual; and yet, strictly speaking, it does not pre-exist, as that cannot be said to pre-exist which sometimes is, and sometimes is not reflected on. But that alone, whatever it be, which thinks, is separate from all else, immortal and eternal; and, because it is impassive, we derive from it no memory. But the impressionable mind, on the contrary, is perishable; and without it there can be no cogitation.