That an immediate influencing among intelligences is impossible, according to the principles of transcendental idealism, stands in no need of proof, nor has any other philosophy rendered such an influence intelligible. Hence nothing remains but to suppose an indirect influence between different intelligences, and here we are concerned merely with the conditions for the possibility of this.Something very interesting happens between pages 160 and 164 (in my edition) of Schelling's System of Transcendental Idealism. Up to that point, the book had put forth a rather straightforwardly Fichtean ontology, awash in pseudo-rigor, wherein the individual self had differentiated itself out of an underlying absolute self through dialectical processes of reflection and (object-)production. But in Part IV, on page 161, Schelling slips in a statement that in effect annihilates subjective idealism as traditionally conceived: "The act of self-determination, or the free action of the intelligence upon itself, can be explained only by the determinate action of an intelligence external to it." A reader who (like me) was lulled into a false complacency by Schelling's painstakingly methodical exposition of Fichteanism would be likely to interpret this claim as yet another indirect restatement of the basic claim that absolute self and individual self (ego in-itself and for-itself) are not the same. (In retrospect, however, this reading ignores the preparatory work Schelling carries out on the previous page.)
Among intelligences which are to act upon each other through freedom, there must, then, in the first place, be a preestablished harmony in regard to the common world which they present. For since all determinacy in the intelligence comes about only through the determinacy of its presentations, intelligences who intuited utterly different worlds would have absolutely nothing in common, and no point of contact at which they could come together ... But now if the intelligence brings forth everything objective out of itself, and there is no common archetype for presentations that we intuit outside us, the consilience among the presentations of different intelligences--as regards both the whole of the objective world and also individual things and events within the same space and time (which consilience alone compels us to ascribe objective truth to our presentations)--is explicable no otherwise than from our common nature...
Through the influence of a rational being, it is not unconscious, but conscious and free activity (which merely glimmers through via the medium of the objective world), that is reflected and becomes an object to us as free. This progressive influence is what we call education, in the widest sense of the word, wherein education is never completed, but persists as a condition of the continuance of consciousness...
- Schelling, System of Transcendental Idealism (1800)
In fact, it is a much simpler and contextually more radical proposition: other minds exist, and the individuum is not the only child of the Absolute. Fichte's teaching is basically a conglomeration of metaphysical subtleties grafted onto a Kantian vocabulary and designed to obscure the fact that it is essentially a solipsism. Fichte, in other words, can't really defend the existence of other minds of equal dignity. Yes, he never tires of repeating that our sense of individuality is only a derivative of its underlying Self, just as the "Not-Self" is—but there's always a sense in which the ego that serves to ground and produce all beings is my ego and mine alone. Schelling's proposition represents a dramatic break with this view. External intelligences originate from the same underlying subjective principle that produces my own intelligence; therefore, they have as much claim upon it as I do.
This sleight-of-hand strips subjective idealism of all its motivating impulses. Fichte had looked at Kant's Ding-an-sich and decided it was unnecessary, that he could ground all of his experience in his own subjectivity. But if we follow Schelling in creating other, equally dignified minds, then there's nothing all that subjective (and hence reliable) about this underlying principle. Its existence is as uncertain as that of external trees and houses. Thus Schelling is faced with the need to refill the absolute with compelling philosophical content in order to salvage it at all. In doing so, he effectively prefigures Hegel's model of subjectivity through recognition: in order for the free self to act freely, the free-ness of its activity must be acknowledged by other equally free selves--a solitary individual, far from being the Fichtean ideal, cannot ever be authentically free. The possibility of this acknowledgement is guaranteed by the fact that the intelligences exist within a preexisting harmony that emerges from the absolute.
In this way, we slip imperceptibly from the realm of ontology to the realm of history. In his practical philosophy, Fichte had appropriated Kant's faculties and categories and plugged them into a chronological-ontogenetic model of development. Schelling takes this chronology, which deals with the abstract evolution of the individual self, and merges it into the flow of a broader history. No longer is each individual merely following his own developmental course: individual evolutions become mere tributaries to a mighty historical river that embodies the groping of the absolute toward something. (Toward what? Hegel hasn't shown up yet, so all we have is unconvincing Kantian meliorism to point the way.)
Is this, then, the root of the nineteenth-century obsession with history? Perhaps not. But is Hegel that root? Or the revolutions? Did history creep in accidentally, as part of a solution to a problem that would soon itself become meaningless? Or was Schelling merely a convenient vehicle for the philosophical irruption of a historical longing that was already being born? Did the absolute stumble upon history in its blind forward rush--or did history dig up from its own depths the evanescent specter of an absolute? Wovon man nicht sprechen kann, darüber muß man schweigen.