This article attempts to develop a rational reconstruction of Kuhn's epistemological relativism which effectively defends it against an influential line of criticism in the work of Shapere and Scheffler. Against the latter's reading of Kuhn, it is argued (1) that it is the incommensurability of scientific problems, data, and standards, not that of scientific meanings which primarily grounds the relativism argument; and (2) that Kuhnian incommensurability is compatible with far greater epistemological continuity from one theory to another than is implied (...) by the criticisms in question. The reconstruction of Kuhn is then used to show that while it constitutes a provocative form of relativism, it can also plausibly account for the sense in which scientific development is rational, involves standards external to particular paradigms, and exhibits progress of a sort. Finally, the article attempts to develop an adequate critical perspective on Kuhn's relativism by distinguishing a ?short?run? from a ?long?run? relativism, and a relativism concerning scientific knowledge from one concerning scientific rationality in Kuhn; the challenge each poses to positi?vist philosophy of science is distinguished and separately evaluated. (shrink)