None the less, in spite of physical resemblance and similar environment, we observe the greatest difference in temperament and in ideas: this side of the human being, then, derives from some quite other Principle [than any external causation or destiny]. A further confirmation is found in the efforts we make to correct both bodily constitution and mental aspirations. Enneads III,1,5
How then do we explain desire and other forms of aspiration? Aspiration must be a motion having its origin in the object aspired to, though some might disallow “origin” and be content with saying that the motion aroused is subsequent to the object; in what respect, then, does aspiring differ from taking a blow or being borne down by a thrust? Perhaps, however, we should divide aspirations into two classes, those which follow intellect being described as Actions, the merely impulsive being Passions. Passivity now will not turn on origin, without or within within there can only be deficiency; but whenever a thing, without itself assisting in the process, undergoes an alteration not directed to the creation of Being but changing the thing for the worse or not for the better, such an alteration will be regarded as a Passion and as entailing passivity. Enneads VI,1,21