Remarks during the Fifth Solvay International Conference on October 1927. "Physics and Beyond: Encounters and Conversations". Book by Werner Heisenberg, pp. 85-86, 1971.
John Stuart Mill (1867). “Thoughts on parliamentary reform. Recent writers on reform. Bain's psychology. A few words on non-intervention. The contest in America. Austin on jurisprudence. Plato”, p.204