Carnap and Phenomenology: What Happened in 1924? A.W. Carus When Carnap first sketched out the Aufbau program, in early 1922, the observational basis of the system was developed phenomenologically. The logical construction of qualities by quasi-analysis only picked up from there; there was no attempt to apply logic directly to subjective sensation itself, as in the published book. 1 In the early phase (1922-24), Carnap distinguished a fixed “primary world” of immediate experience, delineated phenomenologically, from the various “secondary worlds” (or “realities”) that could be constructed by quasi-analysis on this fixed basis. Sometime during 1924 there was a drastic change of course. The distinction between primary and secondary worlds was dropped; Carnap decided that the two-dimensional primary world was every bit as constructed as the secondary worlds, so could not be distinguished as “primary” or more authentically immediate. 2 (In the terms of Der Raum, then, this is the point where intuitive space departs from the stage, leaving only formal and physical space.) 3 At Carnap’s job talk for Vienna, in January 1925, we find a new fundamental principle: “Overcoming Subjectivity [Überwindung der Subjektivität]” as well as a new emphasis on “Unity of the Object Realm [Einheit des Gegenstandbereichs]” (ASP 1925b). And the published book (largely written in 1925) took that route, of course; Russell’s “construction principle,” as Carnap called it, became the book’s motto. Why this abrupt change in the book’s basic approach? There is nothing obviously unstable or inconsistent about applying quasi-analysis to a phenomenologically derived basis. After all, the published Aufbau remained inhomogeneous, too: the ascent from two to three dimensions remained a 1 See more detailed discussion in Carus (2007), pp. 148-54, 160-77. In what follows, archival references are abbreviated as “ASP” or “UCLA”; see bibliography below for list of cited archival items from each source. 2 Carnap 1928, §124; further discussion of this passage and the elimination of the “primary/secondary world” distinction in Carus (2007), pp. 170-71. 3 “In the constitution system the peculiar quality of spatiality, though such an essential feature of the external world in experience, makes no appearance as a quality, any more than other qualities do: colors, pitches, feelings, etc. For the constitution system concerns itself only with the structural, which in the case of space means only with the formal features of this configuration. But nothing knowable, i.e. conceptually capturable, is thereby lost to the constitution system. For the non-structural cannot, according to the thesis of constitution theory, be the object of a scientific statement.” (Carnap 1928, §125)