Abstract
Having for thirty years believed and taught the doctrine of phlogiston… I for a long time felt inimical to the new system, which represented as absurd that which I hitherto regarded as sound doctrine; but this enmity… springs only from force of habit… [Black to Lavoisier, 1791]This paper is abstracted from a forthcoming book which defends a particular answer to the question of just what it is that shifts when a paradigm shifts. The claim is that what shifts are habits of mind. And in particular the claim is that the most striking cases of paradigm shift will characteristically turn on a shift in some single, uniquely critical, habit of mind: the barrier. An account of a radical discovery — discovery that prompts the Kuhnian symptoms of incommensurability, so that intuitions that seem irresistible to some seem perverse to their rivals — then characteristically turns on how some individual got past the barrier (escaped the critical habit of mind), while at least for a while others could not do so.
