and from 1877 professor at Zurich. His masterwork, the Kritik der reinen Erfahrung (‘Critique of Pure Experience’, 2 vols., 1888–90) expounded a particularly rigorous kind of positivism, known as empirio-criticism, which rejects the dualism of perception and the external world in favour of a monism in which all knowledge and thought is confined to pure experience. The system is reminiscent of Hume and, like Hume, Avenarius adds various laws of thought in order to explain the phenomena of cognition. His view was remembered partly because of the attack on its idealist tendency by Lenin, in his Materialism and Empirio-Criticism (1908).