The German physicist and philosopher Friedrich Albert Moritz Schlick (1882-1936) revived positivism as a leading force in 20th-century thought and was the founding spirit of the Vienna Circle.

Moritz Schlick was born in Berlin on Feb. 28, 1833, and educated there. His secondary school training was largely focused on mathematics and physics, and he pursued these subjects further in his university studies at Heidelberg, Lausanne, and Berlin. His doctoral thesis at Berlin, written under Max Planck, was Reflection of Light (1904).

By 1910 Schlick's interests had shifted from physics proper to epistemology and the philosophy of science. With his inaugural dissertation, "The Nature of Truth in the Light of Modern Physics," he began his teaching career at Rostock. There he continued to follow developments in physics, partly through his friendship with Planck and Albert Einstein; and he wrote the first interpretation of the latter's relativity theory in 1917. Also during this period, Schlick...