 The central role on the Vienna Circle’s side in this discussion falls to Carnap and the reorientation of philosophy he sought to effect in Logical Syntax (1934/37). It was the notion of the merely relative and therefore non-apodictic a priori that deeply conditioned his notion of analyticity and allowed him to sidestep Quine’s fallibilist argument in a most instructive fashion. In doing so Carnap built on an idea behind Reichenbach’s early attempt (1920) to comprehend the general theory of relativity by means of the notion of a merely constitutive a priori. Now Schlick had objected to the residual idealism of this proposal (see Oberdan 2009) and prefered talk of conventions instead and Reichenbach soon followed him in this (see Coffa 1991, Ch. 10). Carnap too did not speak of the relative a priori as such (in returning to this terminology present discussions follow Friedman 1994), but his pluralism of logico-linguistic frameworks furnishes precisely that.