Viewed with hindsight, in many respects Brentano belongs to the tradition of Austrian liberalism whose exponents included Mach and Boltzmann. Shared by these thinkers was the endeavour to reform the theory of knowledge in general, and logic in particular, and a scientific conception of the world.1 The mainstream of this tradition flowed through the Vienna Circle, which acknowledged Brentano, Meinong and Höfler among its forerunners. As Neurath recalls, although Brentano started from entirely different premises, he prepared the way for foundational inquiry in logic, mathematics and theory of knowledge. The section of the Vienna Circle's Manifesto devoted to the history of the movement declared: