Abstract
A provocative collection of technical and popular essays dealing with a variety of scientific and political topics which Popper has treated in his major works. For the most part Popper develops, sharpens, and extends to new areas, themes which he has already explored. The major theme running through the essays is that knowledge grows by unjustified and unjustifiable anticipations, guesses and conjectures. These are controlled by criticisms and refutations. Theories can never be positively justified; they can only prove to be resistant to rational criticism. The boldness of Popper's conjectures demands attempted refutations on the part of the reader.--R. J. B.