 To start with, it must be noted that long before the verification principle proper entered the Circle’s discourse in the late 1920s, the thought expressed by Mach’s dictum that “where neither confirmation nor refutation is possible, science is not concerned” (1883 [1960, 587]) was accepted as a basic precept of critical reflection about science. Responsiveness to evidence for and against a claim was the hallmark of scientific discourse. (Particularly the group Frank-Hahn-Neurath, who formed part of a pre-World War I discussion group (Frank 1941, 1949a) sometimes called the “First Vienna Circle” (Haller 1985, Uebel 2003), can be presumed to be familiar with Mach’s criterion.) Beyond this, still in the 1920s, Schlick (1926) convicted metaphysics for falsely trying to express as logically structured cognition what is but the inexpressible qualitative content of experience. Already then, however, Carnap (1928b, §7) edged towards a formal criterion by requiring empirically significant statements to be such that experiential support for them or for their negation is at least conceivable. Meaningfulness meant the possession of “factual content” which could not, on pain of rendering many scientific hypotheses meaningless, be reduced to actual testability. Instead, the empirical significance of a statement had to be conceived of as possession of the potential to receive direct or indirect experiential support (via deductive or inductive reasoning).