 Early philosophical interpretations of the general theory of relativity selected distinct aspects of that theory for favored recognition. Followers of Mach initially lauded Einstein’s attempt to implement a “relativization of inertia” in the general theory, but ultimately were more comfortable with Einstein’s operationalist treatment of the concept of distant simultaneity in the special theory. Kantians and neo-Kantians, if freed from strict fealty to the doctrines of the Transcendental Aesthetic and Transcendental Analytic, pointed to the surpassing importance of certain synthetic “intellectual forms” in the general theory, above all, the principle of general covariance. To an emerging logical empiricism, the philosophical significance of relativity theory was above all methodological, that conventions must first be laid down in order to express the empirical content of a physical theory. In a more far reaching development, already by its completion in November 1915, attempts were made to extend general relativity’s geometrization of gravitational force to non-gravitational interactions, in particular, to electromagnetism. Among these, that of Weyl, and shortly thereafter of Eddington, may be distinguished from others, in particular from Einstein’s many subsequent proposals. Weyl and Eddington aimed not only at a unified field theory, in the sense of a classical field theory in which all fundamental interactions are described by objects of spacetime geometry, but also at reconstructing gravitation and electromagnetism from the epistemological standpoint of a refurbished transcendental idealism.