 The debate between Laudan and Worrall over the value of a fixed methodology of science wonderfully exemplifies the persistence of the ancient problem of change (Laudan 1989; Worrall 1989). How is it possible to explain, or even to measure, change except in terms of an underlying fixity? Doesn’t allowing change at all three of Laudan’s levels—matters of scientific fact and theory, method and standards, and goals—leave us with a damaging relativism? Worrall defends the fixity of Lakatos’s MSRP but agrees that it cannot be established a priori. Laudan’s reticulated model retains a more piecemeal and historically contingent fixity, as described above.