 Like Wittgenstein and Popper, both prior to but especially during the Red Vienna period, Neurath was interested in education and cognitive psychology (like Popper, also in connection with socialist political and social goals). He quickly gained notoriety with his visual method of communication, known as ISOTYPE or Vienna Method. Neurath’s crusade for unified science against speculative metaphysics and the connected challenge of understanding the social and objective nature of scientific knowledge drove him in 1931 to adopt physicalism as the chief constraint on scientific concepts and theories. Physicalism, in a sense broader than Carnap and Schlick’s doctrine of the same term, was the materialist view that science speaks only of observable events, things and processes in space and time. This view set a (normative) bridge intended to unify the truly scientific natural and the social sciences, yet it did not require any reduction to physics. Radical empiricism, by contrast, would only impose the primacy of the subjective, the source of contentiousness, dogmatism and arbitrariness, which he abhorred in speculative metaphysical doctrines. Neurath rejected, along these lines, the language of the unconscious and the ego, subjective mental states devoid of material -physiological-, perceptual or operational correlates. 