 It is true, of course, that in Carnap’s later work on scientific theories and theoretical languages, he distinguishes between a theoretical language and an observation language, and studied the relations between them. What is often overlooked, though, is that even in the Aufbau (and even in the earliest proto-Aufbau manuscripts) Carnap was very clear that what we are to take as “the given” is not inherently fixed or given by nature (as Aristotle would have put it), but something we have to decide on, something we have to specify provisionally in our chosen form of rational reconstruction. Later Carnap became even clearer that what we choose to regard as “observation sentences” is purpose-relative and can’t be decided once for all contexts, in the abstract. As early as “Testability and Meaning” (TM1: §16) Carnap was saying that “there can be several and even mutually exclusive bases” for confirmation by observation. And in later work on the theoretical language this pluralism is extended; in “The methodological character of theoretical concepts” he merely enumerates various possible requirements of different kinds and strengths that might be imposed on the observation language. 