Kedrov has reminded us that the development of knowledge proceeds from appearance to essence. That was also true of the development of notions about space and time. Leibniz, for example, defined space as the order of things existing at the same time. However, that definition is rather superficial, and it is only the development of physics, specifically relativity theory, which made it possible to penetrate more deeply into the nature of space and time and to ascribe a precise and mathematically (...) expressible notion to the well-known judgment to the effect that space and time are forms of the existence of matter. (shrink)