Ekstein's book brings together papers on a number of themes which have occupied his thinking during the last 40 years. In the Wiener Kreis, the Vienna circle of philosophers, he studied, together with his professor Moritz Schlick, the philosophy of science, the analysis of language, and the clarification of meaning. Ekstein's chronological assessment allows us to arrive at a philosophical and psychological clarification of present psycho-therapeutic and psychoanalytic schools.