Doppelt defends the key elements of Kuhn's thesis that scientific revolutions occur when one paradigm is replaced by another and that crucial aspects of competing paradigms are incommensurable. He concedes the merits in the views of those positivist critics of Kuhn who contend that for paradigms to be comparable their proponents must be able to communicate with one another, to agree on a common core of meaning for basic concepts and to deal with shared data and problems. However, he maintains that in identifying the problems which are held to be of fundamental importance and in adopting the standards by which explanatory adequacy is to be evaluated, rival paradigms do not overlap sufficiently for them to have genuine commensurability. This leads Doppelt to accept Kuhn's version of epistemological relativism which maintains that the rationality of the acceptance of new paradigms by the scientific community, at least in the short-run, has an irreducible normative dimension that is strongly conditioned by subjective factors. Doppelt also accepts Kuhn's views with respect to the loss of data, and the question of cumulative progress. The absence of paradigm-neutral external standards allegedly allows each paradigm to assign priority to its own internal standards, thus providing persuasive grounds for the incommensurability of competing paradigms and for epistemological relativism. Nevertheless, he acknowledges that the validity of these arguments over the long term is a contingent issue which can only be resolved by a careful examination of the historical evidence. A chemical revolution took place in the latter part of the eighteenth century when the oxygen theory replaced that based on hypothetical phlogiston. This transition is frequently cited as a typical example of a paradigm - one that illustrates Kuhn's claims for a shift in standards and a loss of data as central features of scientific revolutions. The phlogiston theory held that phlogiston was a normal constituent of air. It explained smelting as the transfer of phlogiston from the air (or from phlogiston-rich charcoal) to the earthy components of the ore, and held that the similar properties of the metallic products could be attributed to their phlogiston content. Combustion, including the calcination of metals and the respiration of living organisms, was viewed as a process involving the release of phlogiston to the atmosphere. The development of improved techniques for collecting gases and for measuring their volume and weight lead to emphasis on precise quantitative methods for evaluating chemical data as distinct from those based on simple quantitative descriptive observations. These developments soon posed difficulties for the phlogiston theory (eg.,the anomalous weight loss during combustion). Eventually, clarification of the composition of water and the use of the 'nitrous air1 test for the ability of a gas to support combustion and respiration (its 'goodness') led to the discovery of oxygen as a component of air and the demonstration that combustion involved combination with an exact quantity of this gas. Within a relatively short period of time, the oxygen theory gained general acceptance and the phlogiston theory was abandoned by most chemists. A critical examination of the events which culminated in the chemical revolution fails to bear out the claim that it was accompanied by a significant loss of empirical data or that it did not represent genuine cumulative progress in scientific knowledge. Instead the history of this revolution indicates that paradigm-neutral external standards for evaluating explanatory adequacy (conservatism, modesty, simplicity, generality, internal and external coherence, refutability, precision, successful predictions) were available and played a crucial role in bringing about this transition. Accumulating evidential warrant played the decisive role in the triumph of the oxygen theory. / Arts, Faculty of / Philosophy, Department of / Graduate