 Carnap’s views on the theoretical language during this period developed in response to critiques and commentaries from (as well as personal correspondence with) C.G. Hempel (1945, 1958, 1963). One response to these interactions was Carnap’s adoption of an idea first suggested by Frank Ramsey (1929) for the purpose of separating the theoretical from the empirical content of a theory; this idea first appeared in print in (the original German version of) Carnap’s paper “Observation language and theoretical language” (1958). (This procedure is explained in detail in the supplement  The Reconstruction of Scientific Theories (Sections 4–6).)  The idea was that a theory could essentially be stated in such a way that all the theoretical terms in it are eliminated, i.e., it could be stated solely in terms of its “empirical residue”. But Carnap’s goal in adopting this method was not to suggest that the theoretical language was eliminable, that theoretical terms could or should be eliminated (as some versions of traditional empiricism might have liked). The point was rather to understand the empirical content of theoretical claims, and its logical function within theories. This leads to many complications, which are still very much under discussion (e.g., Demopoulos 2007, Friedman 2011, Schurz 2005). 