 The worry enters from multiple directions. Perhaps most obviously, it calls into question the down-to-earth realism that Mill endorses within the philosophy of science. Mill’s claim that that the process of science involves finding the structure already present in nature seems at least in tension with the claim that all knowledge is phenomenal and relativized. More subtly, Mill’s basic conception of the relation of mind and world also seems challenged. Mill claims that a priori knowledge is impossible because we cannot know 