This volume is a selection of papers representing the efforts of one student of psychology and of the history and analysis of science, (a) to channel psychology towards the goal of natural science, and (b) to urge that all the constructions of science (descriptions and interpretations) be derived exclusively from contacts with confronted things and events. As the earliest articles indicate, from his first professional concern with psychology, Dr. Kantor has been a reprobative witness of the spiral development of psychology from pure mentalism, through a behavioural era, and back to a modified mentalism. The author has chosen thirty-six papers that have been grouped into eleven sections, each covering important issues within the general scientific or specialised psychological domain. In every case the author's intention was to indicate the direction psychology and the other sciences should go in order to reach a naturalistic status.