 As we saw in  section 6.1,  by the late 1930s Carnap had returned to a consideration of theoretical languages whose primitive terms are not constructed bottom-up from observation sentences at all but entirely top-down, “floating in the air, so to speak” so that these basic theoretical terms can have “only an indirect interpretation, which is incomplete in a certain sense” (Carnap 1939: 65). In Carnap’s mind, the question of confirmation of theories and the question of the empirical content of theories were directly and inseparably connected, as they had been in “Testability and Meaning”. In this subsequent work on these two questions, however, they were pursued separately, and for all of Carnap’s efforts, the two strands could not be joined up. His inductive logic was never able to assign a degree of confirmation other than zero to unrestricted universally quantified theories, which was obviously a defect of the theory and was seized upon by Popper as discrediting the entire enterprise (e.g., Popper 1963). Carnap’s own way around the problem was to argue that scientists often regard the degree by which a piece of evidence E confirms a universal law hypothesis \(\forall x P(x)\) to be given by the degree to which E confirms an “arbitrary” instance of the law \(P(a)\), where a is an individual constant that does not occur in E: see Carnap (1945b: §14). Later authors tried to repair the defect in alternative ways, with varying degrees of success; see the supplement  Inductive Logic.  On the other hand, though Carnap’s work on the empirical content of sentences in a theoretical language often discusses the relations between observational language and theoretical language, he was never quite able to spell out a criterion for empirically meaningful sentences in the theoretical language that did not fall prey to fairly straightforward criticism (e.g., Kaplan 1975). The grand design of connecting up the projects of explicating confirmation and of reconstructing scientific theoretical language remained a distant goal. 