We commonly content ourselves with saying that the same person has distinct faculties of desire and understanding; and to this statement, so far as it goes, no objection can fairly be made. It is equally impossible to derive desire from intellect and intellect from desire; impossible to treat any desire as a mode of understanding, or any act of understanding as a mode of desire. No reason can be given why any perception or conception should lead to desire, unless the soul has to begin with some possibility called into activity by the idea, but other than thta of which the activity constitutes the idea--the perception or conception. And, conversely, we cannot explain how a desire should set intellectual activities in motion except on a corresponding supposition. This being so, we must ascribe to the self-conscious soul or man two equally primitive, co-ordinate, possibilities of desiring and understanding. But we may not regard these as independent of each other, or suppose that one can really exist without the other, since they have a common source in one and the same self-consciousness. The man carries with him into his desires the same single self-consciousness which makes his acts of understanding what they are, and into his acts of understanding the same single self-consciousness which makes his desires what they are. No desire which forms part of our moral experience would be what it is, if it were not the desire of a subject which also understands: no act of our intelligence would be what it is, if it were not the act of a subject which also desires. (§ 130 ¶ 1)

This point would not be worth insisting on, if it meant merely that desires and operations of the intellect mutually succeed each other; that in order to the excitement of desire for an object, as distinct from appetite or instinctive impulse, there must have been a perception, involving at least some elementary acts of memory and inference; and that a desire, again, commonly sets in motion an intellectual consideration of consequences and ways and means. The meaning is that every desire which is within the experience of a moral agent, involves a mode of consciousness the same as that which is involved in acts of understanding; every act of understanding a mode of self-consciousness the same as that which is involved in desire. The element common to both lies in the consciousness of self and a world as in a sense opposed to each other, and in the conscious effort to overcome this opposition. This, however, will seem one of those dark and lofty statements which excite the suspicion of common sense. The reader's patience is therefore requested during one or two paragraphs of explanation. (§ 130 ¶ 2)