A historical example is considered which conflicts with Laudan's Problem Solving Model [1981]. In the period 1840–85 chemists preferred a theory with 3 major conceptual problems (the Liebig Theory of Acids) to Lavoisier's which had only one major conceptual problem (why are the halogen hydrides acids?). The overall conceptual merits of Lavoisier's scheme have been revived in the modern Lux-Flood classification of Acids. Larry Laudan [1977], [1981] proposed a problem solving model of scientific rationality which not only applied to global (...) theories but, if one takes the final paragraph of his [1977] seriously, also applies to sub theories, auxiliary hypotheses and sub auxiliary hypotheses all the way down the line. (shrink)