Antinaturalism rose to dominance in the debate on psychologism among German academic philosophers at the turn of the century. Psychologism, according to received opinion, was decisively refuted by Frege and Husserl. Kusch therefore examines their arguments and, crucially, relates them to the context that shaped that debate and gave those arguments their persuasive force. Drawing on perspectives pioneered by the sociology of scientific knowledge, he reconstructs the dynamics of the psychologism debate; he uncovers its causes and weighs the factors that determine its outcome. What emerges is the fascinating picture of a struggle, between 'pure' philosophy and the newly emerging experimental psychology, for academic status, social influence and institutional power. The triumph of antinaturalism, far from being the only logical conclusion, was dependent on historical contingency. Introducing forms of analysis new to the history of philosophy, psychologism will make fascinating reading for lecturers and students of philosophy, psychology, sociology and cognitive science; it will also stimulate renewed debate on the prospects of antinaturalism at the close of this century.