Whereupon let us recognize that it is almost forbidden to human reason to stray in these regions; and that the part of a prophet is, next to that of a commentator of prophecies, one of the most difficult and thankless that a man can attempt to sustain the world's stage. 24 I am not sure if it is really necessary, before closing this chapter, to follow in the wake of many others and broach the problem of the preexistence of the future, which includes those of fatality, of free will, of time and of space, that is to say, all the points that touch the essential sources of the great mystery of the universe. The theologians and the metaphysicians have tackled these problems from every side without giving us the least hope of solving them. Among those which life sets us, there is none to which our brain seems more definitely and strictly closed; and they remain, if not as unimaginable, at least as incomprehensible as on the day when they were first perceived. What corresponds, outside us, with what we call time and space? We know nothing about it; and Kant, speaking in the name of the "apriorists," who hold that the idea of time is innate in us, does not teach us much when he tells us that time, like space, is an a priori form of our sensibility, that is to say, an intuition preceding experience, even as Guyau, among the "empiricists," who consider that this idea is acquired only by experience, does not enlighten us any more by declaring that this same time is the abstract formula of the changes in the universe. Whether space, as Leibnitz maintains, be an order of coexistence and time an order of sequences, whether it be by space that we succeed in representing time or whether time be an essential form of any representation, whether time be the father of space or space the father of time, one thing is certain, which is that the efforts of the Kantian or neo-Kantian apriorists and of the pure empiricists and the idealistic empiricists all end in the same darkness; that all the philosophers who have grappled with the formidable dual problem, among whom one may mention indiscriminately the names of the greatest thinkers of yesterday and to-day--Herbert Spencer, Helmholtz, Renouvier, James Sully, Stumpf, James Ward, William James, Stuart Mill, Ribot, Fouillee, Guyau, Bain, Lechalas, Balmes, Dunan and endless others--have been unable to tame it; and that, however much their theories may contradict one another, they are all equally defensible and alike struggle vainly in the darkness against shadows that are not of our world. 25