It is not usually our ideas that make us optimists or pessimists, but it is our optimism or our pessimism, of physiological or perhaps pathological origin, as much the one as the other, that makes our ideas. Man is said to be a reasoning animal. I do not know why he has not been defined as an affective or feeling animal. Perhaps that which differentiates him from other animals is feeling rather than reason. More often I have seen a cat reason than laugh or weep. Perhaps it weeps or laughs inwardly--but then perhaps, also inwardly, the crab resolves equations of the second degree. And thus, in a philosopher, what must needs most concern us is the man. Take Kant, the man Immanuel Kant, who was born and lived at Königsberg, in the latter part of the eighteenth century and the beginning of the nineteenth. In the philosophy of this man Kant, a man of heart and head--that is to say, a man--there is a significant somersault, as Kierkegaard, another man--and what a man!--would have said, the somersault from the _Critique of Pure Reason_ to the _Critique of Practical Reason_. He reconstructs in the latter what he destroyed in the former, in spite of what those may say who do not see the man himself. After having examined and pulverized with his analysis the traditional proofs of the existence of God, of the Aristotelian God, who is the God corresponding to the _zôon politikon_, the abstract God, the unmoved prime Mover, he reconstructs God anew; but the God of the conscience, the Author of the moral order--the Lutheran God, in short. This transition of Kant exists already in embryo in the Lutheran notion of faith. The first God, the rational God, is the projection to the outward infinite of man as he is by definition--that is to say, of the abstract man, of the man no-man; the other God, the God of feeling and volition, is the projection to the inward infinite of man as he is by life, of the concrete man, the man of flesh and bone. Kant reconstructed with the heart that which with the head he had overthrown. And we know, from the testimony of those who knew him and from his testimony in his letters and private declarations, that the man Kant, the more or less selfish old bachelor who professed philosophy at Königsberg at the end of the century of the Encyclopedia and the goddess of Reason, was a man much preoccupied with the problem--I mean with the only real vital problem, the problem that strikes at the very root of our being, the problem of our individual and personal destiny, of the immortality of the soul. The man Kant was not resigned to die utterly. And because he was not resigned to die utterly he made that leap, that immortal somersault,[5] from the one Critique to the other.