Dual Theories: ‘Same But Different’ or ‘Different But Same’?

I argue that, under the glitz, dual theories are examples of theoretically equivalent descriptions of the same underlying physical content: I distinguish them from cases of genuine underdetermination on the grounds that there is no real incompatibility involved between the descriptions. The incompatibility is at the level of unphysical structure. I argue that dual pairs are in fact very strongly analogous to gaugerelated solutions even for dual pairs that look the most radically distinct, such as AdS/CFT.