This book demonstrates that Karl Popper's philosophy of science, with its emphasis on the method of trial and error, is largely based on the psychology of Otto Selz. Selz's theory of problem solving and scientific discovery laid the foundation for much of contemporary cognitive psychology. This original analysis covers Popper's early writings before he began his career as a philosopher.

Wittgenstein's aphoristic style holds great charm, but also a great danger: the reader is apt to glean too much from a single fragment and too little from the fragments as a whole. In my first confron tations with the Philosophical Investigations I was such a reader, and so, it turned out, were most of the writers on Wittgenstein's later philosophy. Wittgenstein's remarkable ability to bring together many facets of his thought in one fragment is fully exploited in the critical literature; but hardly any attention is paid to the connection with other fragments, let alone to the many hitherto...