Causal theories of reference in the philosophy of language and philosophy of science have suggested that it could resolve lingering worries about incommensurability between theoretical claims in different paradigms, to borrow Kuhn’s terms. If we co-refer throughout different paradigms, then the problems of incommensurability are greatly diminished, according to causal theorists. I argue that assuring ourselves of that sort of constancy of reference will require comparable sorts of cross-paradigm affinities, and thus provides us with no special relief on this problem. (...) Suggestions on how to think about rigid designation across paradigms are included. (shrink)