Abstract

On the usual philosophical story, gauge theories are puzzling because they seem to have "surplus structure": theoretical content that does not directly correspond to features of the world.  

Prima facie, this is only a puzzle for a scientific realist: the instrumentalist is indifferent to this sort of correspondence.  Nevertheless, I argue, puzzles about gauge theories indeed arise for some contemporary versions of instrumentalism.  In particular, there is a problem concerning the interpretation of the physicist's distinction between "gauge" and "physical" symmetries.  

I offer a new interpretation of this distinction that has payoffs for current debates in philosophy of physics.