 In the Aufbau the construction of matter from “elementary experiences”, and later Nelson Goodman (1951) continued the project. Michael Friedman (1999) and Alan Richardson (1998) have argued that Carnap’s project of construction owed much more to his background in neo-Kantian issues about the “constitution” of empirical objects than with Russell’s project. See, however, Pincock (2002) for a response that argues for the importance of Russell’s project of reconstructing scientific knowledge in (Carnap 1967). More generally, the use of set theoretic constructions became widespread among philosophers, and continues in the construction of set theoretic models, both in the sense of logic where they model formal theories and to provide descriptions of truth conditions for sentences about entities.