 Einstein addressed this issue in several popular writings during the 1920s, in particular, the famous lecture Geometrie und Erfahrung (Einstein 1921, see also Einstein, 1923, Einstein, 1924, Einstein 1926; Einstein 1926; see Giovanelli 2014 for an overview). Sub specie temporis, he argued, it was useful to compare the geometrical/kinematical structures of the theory with experience separately from the rest of physics. Sub specie aeterni, however, only geometry and physics taken together can be said to be ‘true or false.’ This epistemological model became more appropriate, while Einstein was moving beyond general relativity in the direction of theory unifying the gravitational and the electromagnetic field. Einstein had to rely on progressively more abstract geometrical structures which could not be defined in terms of the behavior of some physical probes. Thus, the use of such structures was justified because of their role in the theory as a whole. In the second half of the 1920s, in correspondence with Reichenbach (Giovanelli 2017) and Meyerson (Giovanelli 2018), Einstein even denied that the very distinction between geometrical and non-geometrical is meaningful (Lehmkuhl 2014). 