In most of the histories of philosophy that I know, philosophic systems are presented to us as if growing out of one another spontaneously, and their authors, the philosophers, appear only as mere pretexts. The inner biography of the philosophers, of the men who philosophized, occupies a secondary place. And yet it is precisely this inner biography that explains for us most things.

It behoves us to say, before all, that philosophy lies closer to poetry than to science. All philosophic systems which have been constructed as a supreme concord of the final results of the individual sciences have in every age possessed much less consistency and life than those which expressed the integral spiritual yearning of their authors.

And, though they concern us so greatly, and are, indeed, indispensable for our life and thought, the sciences are in a certain sense more foreign to us than philosophy. They fulfil a more objective end—that is to say, an end more external to ourselves. They are fundamentally a matter of economics. A new scientific discovery, of the kind called theoretical, is, like a mechanical discovery—that of the steam-engine, the telephone, the phonograph, or the aeroplane—a thing which is useful for something else. Thus the telephone may be useful to us in enabling us to communicate at a distance with the woman we love. But she, wherefore is she useful to us? A man takes an electric tram to go to hear an opera, and asks himself, Which, in this case, is the more useful, the tram or the opera?

Philosophy answers to our need of forming a complete and unitary conception of the world and of life, and as a result of this conception, a feeling which gives birth to an inward attitude and even to outward action. But the fact is that this feeling, instead of being a consequence of this conception, is the cause of it. Our philosophy—that is, our mode of understanding or not understanding the world and life—springs from our feeling towards life itself. And life, like everything affective, has roots in subconsciousness, perhaps in unconsciousness.

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 ζωον πολιτικον, 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.