On Symmetry and Duality

We advocate an account of dualities between physical theories: the basic idea is that dual theories are isomorphic representations of a common core. We defend and illustrate this account, which we call a Schema, in relation to symmetries. Overall, the account meshes well with standard treatments of symmetries. But the distinction between the common core and the dual theories prompts a distinction between three kinds of symmetry: which we call `stipulated', `accidental' and `proper'.
Comment: 44 pages. Published in Synthese, in a special issue on `Symmetries and Asymmetries in Physics' edited by M. Frisch, R. Dardashti, and G. Valente