The question which finally emerges, as the result of Dewey's inquiry, is this: What is the nature of this self-activity which is more than the mere category of self-consciousness? "As long as sensation was regarded as given by a thing-in-itself, it was possible to form a conception of the self which did not identify it with the world. But when sense is regarded as having meaning only because it is 'there' as determined by thought, just as thought is 'there' only as determining sense, it would seem either that the self is just their synthetic unity (thus equalling the world) or that it must be thrust back of experience, and become a thing-in-itself. The activity of the self can hardly be a third something distinct from thought and from sense, and it cannot be their synthetic union. What, then, is it?"[51] Green, Dewey says, attempted to solve the difficulty by his "idea of a completely realized self making an animal organism the vehicle of its own reproduction in time."[52] This attempt was at least in the right direction, acknowledging as it did the fact that the self is something more than the highest category of thought. Dewey admits his difficulties in a way that makes extended comment unnecessary. He does not challenge the validity of the Hegelian development of the Kantian categories, but proposes to make more of the self than the Hegelians ordinarily do. This synthetic self-activity must reveal itself as a concrete process; that is one of the demands of his psychological standpoint. It is impossible to foresee what this process would be as an actual fact of experience.