The main answers given to the problem of space and time are: 1. The realist, according to which space and time are forms of existence of matter. 2. For positivism, space and time are concepts convenient for the description of phenomena. For Poincare, to take a notorious case, "the characteristic property of space, that of having three dimensions, is only a property of our distribution board, a property residing, so to speak, in the human intelligence. The destruction of some of these connections, that is to say, of these associations of ideas, would be sufficient to give us a different distribution board, and that might be enough to endow space with a fourth dimension" [1]. According to E. Borel, on the other hand, "it is convenient to use intervals, just as it is convenient to assume that the earth is rotating and the sun is standing still (to a first approximation). Moreover we must not forget that for Poincare convenience is identical to scientific truth" [2]. Hume, Mach, Poincare, Wittgenstein, the multiform schools of classical and modern positivism, deprived the concepts of space and time of their ontic counterpart. 3. Kant, on the contrary, was, from a certain point of view, a realist. He accepted the existence of the things in themselves, independent of the subject. For him, however, space and time are the a priori forms of the intuition. They are not forms of existence of matter.
I will not try to refute the conception of positivism [3]. The case of Kant is more delicate and interesting and I will try to confront it with that of Einstein. For comtemporary realism and materialism, the realist Einstein is right. Not Kant. However the problem is not so simple. So, in order to discuss it, let us at first summarize the Kantian conception.
