In late 1924, Carnap radically changed the Aufbau framework. Up to then, the logical construction of "realities" or "secondary worlds" by quasi-analysis had proceeded on the basis of a fixed, phenomenologically articulated "primary world." This distinction disappears in 1924, and logical construction is now applied directly to the basis itself, following the published book's Russellian motto, "Wherever possible, logical constructions are to be substituted for inferred entities." This paper first reviews the available documentary evidence for this radical change, but finds only hints, which are then placed in the larger context of Carnap's development during this period.