 Reichenbach’s account of the ascension from sense data to individual things to scientific theories is via an account of testing, in spirit close to ideas that Hermann Weyl (1927) and Rudolf Carnap (1936) were later to advance, in which various hypotheses support one another, each functioning as an auxiliary in tests of others, an idea Glymour (1980) later unsuccessfully tried to formalize as “bootstrapping.” The foundational character of sense data and the view that objects and their properties and relations are constructions endures for some years in Reichenbach’s thought, for example in his 1929 essay on “The Aims and Methods of Physical Knowledge” (1929g), where, however, the example and authority is no longer Kant’s first Critique but rather Russell’s Our Knowledge of the External World (1914) and Carnap’s The Logical Structure of the World (1928). 