The affective part of the soul, therefore, is not corporeal; it is a form indeed, but a form engaged in matter, such as the appetite, the power of growth, both nutritive and generative, a power which is the root and principle of appetite, and the affective part of the soul. Now a form cannot undergo an affection or a passion, but must remain what it is. It is the matter (of a body) which is capable of being affected by a “passion” (an affection), when this affection is produced by the presence of the power which is its principle. Indeed it is neither the power of growth that grows, nor the nutritive power that is fed; in general, the principle that produces a motion is not itself moved by the movement it produces; in case it were moved in any way, its movement and action would be of an entirely different nature. Now the nature of a form is an actualization, by its mere presence producing (something), just as if the harmony alone could cause the vibration of the strings of a lyre. Thus the affective part (of the soul, without itself being affected) is the cause of the affections, whether the movement proceed from it, that is, from SENSE-IMAGINATION, or whether they occur without (distinct) imagination. (Ennead III,6 (26) 4)