  Theoretical equivalence and duality are two closely related notions: but
their interconnection has so far not been well understood. In this paper I
explicate the contribution of a recent schema for duality to discussions of
theoretical equivalence. I argue that duality suggests a construal of
theoretical equivalence in the physical sciences. The construal is in terms of
the isomorphism of models, as defined by the Schema. This construal entails
interpretative constraints that should be useful for theoretical equivalence
more generally. I illustrate the construal in various formulations of Maxwell's
electromagnetic theory.
