The principle of equivalence

start from John Norton's analysis (1985) of the reach of Einstein's version of the principle of equivalence which is not a local principle but an exte nsion of the relativity principle to reference frames in constant accelerat ion on the background of Minkowski spacetime. We examine how such a point o f view implies a profound, and not generally recognised, reconsideration of the concepts of inertial system and field in physics. We then reevaluate t he role that the infinitesimal principle, if adequately formulated, can leg itimately be claimed to play in general relativity. We show that what we ca ll the 'punctual equivalence principle' has significant physical content an d that it permits the derivation of the geodesic law. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.