In this article I discuss a recent argument due to Dan McArthur, who suggests that the charge that Michael Friedman’s relativised a priori leads to irrationality in theory change can be avoided by adopting structural realism. I provide several arguments to show that the conjunction of Friedman’s relativised a priori with structural realism cannot make the former avoid the charge of irrationality. I also explore the extent to which Friedman’s view and structural realism are compatible, a presupposition of McArthur’s argument. (...) This compatibility is usually questioned, due to the Kantian aspect of Friedman’s view, which clashes with the metaphysical premise of scientific realism. I argue that structural realism does not necessarily depend on this premise and as a consequence can be compatible with Friedman’s view, but more importantly I question whether Friedman’s view really implies mind dependence. (shrink)