 The question of unity engaged science and philosophy alike. In the 20th century the unity of science became a distinctive theme of the scientific philosophy of logical empiricism. Logical empiricists—known controversially also as logical positivists—and most notably the founding members of the Vienna Circle in their Manifesto adopted the Machian banner of “unity of science without metaphysics”, a normative criterion of unity with a role in social reform based on the demarcation between science and metaphysics: the unity of method and language that included all the sciences, natural and social. A common method did not necessarily imply a more substantive unity of content involving theories and their concepts.