But just here our confession of doubt has reached a critical stage; since in experience apparently at its very worst, as if in a medley of discords we have caught a promise of real harmony, and so something from which to get genuine hope. In the very habit of duplicity or contradiction we have again and again had suggestion of an agent of validity, a power for adequacy in experience, which would hold even a phenomenal, relative, partial experience to a real world. In short, really the strongest reason for doubt is possibly a ground of belief; or, as was said in substance at the close of the foregoing chapter, the very experience of which we are already confirmed doubters is, after all, just the experience which we seem to see our way to believing in. Since the time of the great Leibnitz, and probably since the time self-conscious man drew his first breath, all genuine optimism has caught its most assuring vision of what was good, not in something quite apart from what was evil, but in and through evil itself, as if what is evil must be ever building better than it seems or than it knows. Very much as mathematics has viewed the negative quantity as an integral part of the whole system of quantities, so in the person of Leibnitz--statesman, historian, scientist, mathematician, and philosopher--and I imagine in the person also of you or me, though we may not claim the same [p.134] authority, the human mind has been wise and deep enough to see evil, representing all the negative things of life as an organic part of the best possible world, even of the world created by an infinite God. At least since Leibnitz's time, I say, optimism has generally justified itself, not by denial of evil in the world, but in and through evil. Not long ago a young man who was perhaps more profound and reflective in his habits of mind than wise in his manner of statement, said to me that the most spiritual truth as yet disclosed to him was the identity of God with the devil. A shocking declaration, of course; yet, to say the least, not very far from the very spiritual idea, welcome to most, if not to all, that the conviction of sin is the beginning of salvation, or that the consciousness of ignorance is the very ground of wisdom. And here, similarly, belief within doubt, not belief apart from doubt, or validity and reality only in a contradictory experience, not aloof from a contradictory experience, is the sum and substance of what our confession has certainly been leading towards.