Kant's first critics put their finger on the weak point of his system, the thing in itself. So, assuming it to be discarded, Fichte set to work on new lines, the lines of pure idealism. But, though an idealist, he is not, any more than Berkeley, a solipsist. The celebrated {104} antithesis of the ego and the non-ego dates from him, and strikes the keynote of his whole system. It might be thought that, as compared with the old realism, this was a distinction without a difference. But that is not so; for, according to Fichte, the non-ego is subjective in its origin, and that is where he departs widely from Berkeley's theological idealism. Not that I create the not-myself; I _assume_ it as the condition of my self-consciousness--a remarkable feat of logic, but after all not more wonderful than that space and time should result from the activity of the outer and inner senses. This figment of my imagination is anyhow solid enough to beget a new feeling of resistance and recoil, throwing the self back on itself, and bringing with it the interpretation of that external impact by the category of causation, of its own activity as substance, and of the whole deal between the ego and the non-ego as interaction or reciprocity. In this way the first triad of thesis, antithesis, and synthesis is obtained; and from this, by a vast expenditure of ingenuity, the whole array of Kant's forms, categories, and faculties is evolved as a coherent system of scientific thought in obedience to a single principle--the self-realisation of the ego, alternatively admitting and transcending a limit to its activity.