 Part of the classical structuralist program consists in the idea that philosophy of science, properly construed, pursues an ideal of rational reconstruction of science (cf. Stegmüller 1979; Balzer 1984: 331), which is to be understood as a reconstruction of actual scientific developments. Since it is common knowledge that cases of straightforward reductions are rare, if they exist at all, structuralists focused primarily on cases of mere replacement or on similarities between theories, which are cashed out in terms of approximation or (semantic counterparts of) derivation under ideal conditions (Moulines 1984; Scheibe 1999; Stegmüller 1979 &amp; 1986: ch. 4).