Moritz Schlick studied at Berlin under Max Planck (see Vol. 5) and received his Ph.D. in physics in 1904. He taught at Rostock and Kiel before joining the faculty at Vienna in 1922. His early work, General Theory of Knowledge (1918), reveals his commitment to realism and to the experimental method in scientific and philosophical knowledge. At Vienna he led the Vienna Circle of logical positivism and was instrumental in recruiting Rudolf Carnap. The publication of Ludwig Wittgenstein's Tractatus Logico-Philosophicus (1921) influenced radically the subsequent development of his thought. Increasingly he stressed the empirical verification criterion for truth and meaning and became severely critical of statements in philosophy and elsewhere that could not meet this criterion. Hence the logical positivists whom he led became notorious for their thesis that metaphysics in non-sense. His mature epistemology was presented in the publication of the second edition of his General Theory of Knowledge (1925). He also advanced a noncognitivist theory of ethical statements in his book Problems of Ethics (1939).
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