Book I: Metaphysics of Knowledge.
Chapter I: The Spiritual Principle in Knowledge and Nature.
§ 32.
Thus, in order that successive feelings may be related objects of experience, even objects related in the way of succession, there must be in consciousness an agent which distinguishes itself from the feelings, uniting them in their severalty, making them equally present in their succession. And so far from this agent being reducible to, or derivable from, a succession of feelings, it is the condition of the existence of that relation between feelings, as also of those other relations which are not indeed relations between feelings, but which, if they are matter of experience, must have their being in consciousness. If there is such a thing as a connected experience of related objects, there must be operative in consciousness a unifying principle, which not only presents related objects to itself, but at once renders them objects and unites them in relation to each other by this act of presentation; and which is single throughout the experience. The unity of this principle must be correlative to the unity of the experience. If all possible experience of related objects—the experience of a thousand years ago and the experience of to-day, the experience which I have here and that which I might have in any other region of space—forms a single system; if there can be no such thing as an experience of unrelated objects; then there must be a corresponding singleness in that principle of consciousness which forms the bond of relation between the objects. (§ 32 ¶ 1)