21. That this is the phase of the human being in which desire takes its origin is shown by observation of the different stages of life; in childhood, youth, maturity, the bodily desires differ; health or sickness also may change them, while the [psychic] faculty is of course the same through all: the evidence is clear that the variety of desire in the human being results from the fact that he is a corporeal entity, a living body subject to every sort of vicissitude.
The total movement of desire is not always stirred simultaneously with what we call the impulses to the satisfaction even of the lasting bodily demands; it may refuse assent to the idea of eating or drinking until reason gives the word: this shows us desire – the degree of it existing in the living body – advancing towards some object, with Nature [the lower soul-phase] refusing its co-operation and approval, and as sole arbiter between what is naturally fit and unfit, rejecting what does not accord with the natural need.
We may be told that the changing state of the body is sufficient explanation of the changing desires in the faculty; but that would require the demonstration that the changing condition of a given entity could effect a change of desire in another, in one which cannot itself gain by the gratification; for it is not the desiring faculty that profits by food, liquid, warmth, movement, or by any relief from overplenty or any filling of a void; all such services touch the body only.