An excerpt from the book by Henri Lefebvre introduces the basic principle of his theory  and  what is followed by explanations and implications. The main point -- space (social) is the product (social) -- is considered in the problematic vein. The author wonders about what hides this truth of (social) space, which consists in that it is the product (social). His response is --  a double illusion, each side of which suggests another, reinforce each, it is justified: first, the illusion of transparency, and second -- of density ("realistic" illusion). What follows is a detailed analysis of these illusions.