  The classical theory of physical geometry, developed by  Helmholtz, Poincaré and Hilbert, regarded the concept of  “metric congruence” as the only basic relation of  geometry, and constructed physical geometry from this one notion  alone in terms of the relative positions and displacements of  physical congruence standards. Although Einstein’s general theory of  relativity championed a dynamical view of spacetime  geometry that is very different from the classical theory of physical geometry, Einstein initially approached the problem of  the structure of spacetime from the metrical point of view. It was  Weyl (1923b) who emphasized and developed the metric-independent  construction of the symmetric linear connection and who pointed out  the rationale for doing so. In both the non-relativistic and  relativistic contexts, it is the symmetric linear connection, and not the metric, which plays the essential role in the formulation of all  physical laws that are expressed in terms of differential equations.  It is the symmetric linear connection that relates the state of a  system at a spacetime point to the states at neighboring spacetime  events and enters into the differentials of the corresponding  magnitudes. In both Newtonian physics and the theory of general  relativity, all dynamical laws presuppose the projective and affine  structure and hence the Law of Inertia. In fact, the whole of tensor  analysis with its covariant derivatives is based on the affine  concept of infinitesimal parallel displacement and not  on the metric. 