The Logical Theory of Canonical Maps: The Elements & Distinctions Analysis of the Morphisms, Duality, Canonicity, and Universal Constructions in Set

Abstract

Category theory gives a mathematical characterization of naturality but not of canonicity. The purpose of this paper is to develop the logical theory of canonical maps based on the broader demonstration that the dual notions of elements & distinctions are the basic analytical concepts needed to unpack and analyze morphisms, duality, canonicity, and universal constructions in Set, the category of sets and functions. The analysis extends directly to other Set-based concrete categories (groups, rings, vector spaces, etc.). Elements and distinctions are the building blocks of the two dual logics, the Boolean logic of subsets and the logic of partitions. The partial orders (inclusion and refinement) in the lattices for the dual logics define the canonical morphisms (where `canonical' is always relative to the given data, not an absolute property of a morphism). The thesis is that the maps that are canonical in Set are the ones that are defined (given the data of the situation) by these two logical partial orders and by the compositions of those maps.