Justus von Liebig (1859). “Familiar Letters on Chemistry, in its relation to Physiology, Dietetics, Agriculture, Commerce and Political Economy: Edited by John Blyth”, p.5
"New Studies in Philosophy, Politics, Economics and the History of Ideas". Book by Friedrich Hayek. Part I: "Philosophy ". Chapter 2: "The Pretence of Knowledge", p. 24, 1978.