 In this early stage of what became the Aufbau project, Carnap still followed Vaihinger in distinguishing sharply between the direct, genuine, first-hand knowledge of the “chaos” and the fictive, constructed nature of “reality”. But he put the boundary between them in a different place. This was because Husserl’s phenomenology offered an escape route from Vaihinger’s completely undifferentiated chaos. It yielded certain distinctions within the chaos (e.g., between “living” and “dead” experience) that could claim a degree of objectivity. These distinctions, Carnap then thought, were not fictional, but actually extended the range of what could be genuinely known, even without fictions, just from the chaos itself. So Carnap’s boundary between the immediately known primary world (of sensory “chaos” plus a minimal, phenomenologically extrapolated structure) and a fictive secondary world of “reality” included more in the “primary” sector than Vaihinger’s. Carnap thought he could show on phenomenological grounds that the primary world is two-dimensional in all sense modalities (Carnap 1924). So the boundary between the fixed primary world and the freely choosable secondary worlds (“realities”) was located at the ascent from two to three dimensions. Within the primary world, the construction proceeded entirely by explicit definition, beginning from the qualities obtained by quasianalysis. Secondary worlds, by contrast, are not uniquely determined. The construction of a secondary world proceeds, rather, by optimizing its fit to whichever fictions are chosen to guide the construction, subject to the constraint of the (fixed) primary world. 