But the division of the unreasoning phase of the soul into a desiring faculty and a passionate faculty — the first identical with the vegetal principle, the second being a lower phase of it acting upon the blood or bile or upon the entire living organism — such a division would not give us a true opposition, for the two would stand in the relation of earlier phase to derivative.
This difficulty is reasonably met by considering that both faculties are derivatives and making the division apply to them in so far as they are new productions from a common source; for the division applies to movements of desire as such, not to the essence from which they rise.
That essence is not, of its own nature, desire; it is, however, the force which by consolidating itself with the active manifestation proceeding from it makes the desire a completed thing. And that derivative which culminates in passion may not unreasonably be thought of as a vestige-phase lodged about the heart, since the heart is not the seat of the soul, but merely the centre to that portion of the blood which is concerned in the movements of passion.