in the letter. When I say that he must verify these doctrines in his own consciousness, I mean that he must actively reproduce and realise them in his own thoughts, together with the grounds on which they rest. He must be able to place himself in the mental circumstances in which they arose, and must observe them springing up in his own mind, just as they sprang up in the minds of those who originally propounded them. They must be to him, not the dead dogmas of their thinking, but the living products of his own. They must come to him not as antiquated traditions, but as teeming with present interest, and as fraught with a present and inextinguishable vitality. As an original thinker, he must reanimate these doctrines from within, while, as a critic and historian, he is engaged in receiving and deciphering them from without. What he receives from others he must also find as the indigenous growth of his own mind. What he must be able to say to himself is this: Such a system, or such a doctrine, or such a problem, is not what some individual thinker has chosen to think, or has accidentally thought, but it is what thinking itself, in certain circumstances, must inevitably think. It is only when he conceives and executes his vocation in this spirit that the historian of philosophy can be regarded as having verified and reanimated the systems which he is expounding. When he has so verified them—verified them in the manner thus imperfectly described—he has obeyed the primary obligation by which the historian of
