"My wildest dreams have been fulfilled," wrote a jubilant Einstein in early December 1915 to his dear friend Michele Besso (Speziali, 1972, p. 60) "General covariance. Perihelion motion of Mercury wonderfully exact. . .," he continued, checking off the achievements that brought to a dramatic and successful close nearly three years of snuggle with his general theory of relativity, during which time he had mistakenly come to believe that he must forgo general covariance. The general covariance of his theory was to be stressed by Einstein as one of its most distinctive properties and, in particular, the one that gave mathematical expression to the theory’s extension of the principle of relativity to all states of motion. He explained this connection to the principle of relativity in lectures he gave at Princeton University: We shall be true to the principle of relativity in its broadest sense if we give such a form to the laws that they are valid in every such fourdimensional system of coordinates, that is, if the equations expressing the laws are covariant with respect to arbitrary transformations. (Ein— stein 1922, p. 60) Such proclamations are common in Einstein’s work} Unfommately, they have proved to be a problem for later commentators who seek to understand Einstein’s views because it is now commonplace for any reasonably coherent space-time theory to have a generally-covariant formulation. One need only formulate it by the standard methods of modern differential geometry. Since these generally—covaiiant theories include the versions of Newtonian space-time theory that tmequivocally violate...