This work examines affinity theories espoused by British chemists of the 18th Century, exposing a degree of theoretical variation at odds with the received view of a unified, monolithic 'affinity theory'. Showing that affinity was valued for its utility and its ability to guide chemical practice, it explains how theories were formulated specifically to assist the chemist at an operational level. This work explores the roles assigned to affinity in chemical practice and, in particular, in chemical pedagogy. It traces a complex structure of correspondences and divergences amongst affinity theories by comparing theoretical components performing the same operational role within different theories. In spite of the evident variations amongst affinity theories, a public consensus still held throughout the 18th century. The lack of controversy is evidence of an array of predominantly tacit concepts forming part of each theory to which all subscribed; this "common ground" was at the heart of the apparent public consensus. The work shows how in due course affinity became a fundamental part of the chemical norm to which the majority of chemists assented.