This chapter is devoted to an analysis of mathematics as a distinct domain of objective mental reality, which is grounded in a quantitative mode of representing the world. The quantitative entities of mathematics (and the world) are formed on the basis of a single universal property—calculability—which allows any qualitative entity and its characteristics to be translated into uniform measurable sets. Thanks to this, consciousness is capable of perceiving any entity as a set of abstract countable elements, thereby constructing quantitative models of the world. Unlike the qualitative approach, which captures the unique, sensually representable properties of entities, quantitative symbolic representation reduces them to sets that can compare quantitative entities, or sets, according to a single parameter—cardinality, that is, the property of countability. Quantitative representation produces a particular projection of the world, that only captures the relationships between new kinds of entities—sets. Although these sets are, by their nature, mental entities, in physical reality they possess firm referents and can therefore often be directly correlated with it. Mathematical creativity, which may at first seem detached from the familiar, sensory-based picture of the world, unexpectedly gives rise to models suitable for describing fragments of reality. This can be explained by the fact that there are objective relations and dependencies in the world between the physical referents of mathematical objects and constructions. Mathematics is an autonomous domain of objective mental reality that reveals the hidden structure of the world. However, looking for correspondences between its constructions and fragments of reality is usually a complex and intuitive process.