 The actual detailed construction of the autopsychological realm occupies only a small part of the book. The first sections focus largely on what Carnap would later call “clarification of the explicandum” (see  section 1.1  above). Carnap considers various options for the choice of basic elements (the elements or building blocks of which everything is to be constructed) and basic relations (the relations between and among these building blocks that is to effect the construction). The radicalism of Carnap’s push for simplification is expressed by his choice of only a single kind of basic elements, “elementary experiences”, and a single basic relation, “recollection of similarity”. The elementary experiences were not isolated “sense data” of traditional empiricism (the isolated pitch and timbre of momentary sounds or colored points of the visual field that we find in Hume or Mach), but holistic time slices of total experience, from which nothing has yet been abstracted; Carnap was here attempting to do justice to the psychology courses he had taken as an undergraduate, where he had learned about the new directions taken in Gestalt psychology by Köhler, Koffka, and others. By quasianalysis, an abstraction technique formalizing Russell’s “principle of abstraction”, (see the supplement  Methodology (Section 3))  the similarities among these time-slices could retrospectively be grouped (by repeated application of the basic relation, recollection of similarity) into something like equivalence classes of, say, a certain color or a certain smell that were sufficiently similar. By this means Carnap constructs the subjective cognitive world of a single mind in some detail, up to the point where, on that basis, a three-dimensional objective world of space-time can be constructed (see the supplement  Aufbau (Section 2)  for more detail concerning some of these constructions).