Joseph A. Schumpeter (2011). “The Theory of Economic Development: An Inquiry into Profits, Capital, Credit, Interest, and the Business Cycle”, p.19, Transaction Publishers
Henry Ward Beecher, Augusta Moore (1859). “Notes from Plymouth Pulpit: A Collection of Memorable Passages from the Discourses of Henry Ward Beecher, with a Sketch of Mr. Beecher and the Lecture Room”, p.57
Alan Greenspan's address to the Federal Reserve Bank of Chicago's Forty-first Annual Conference on Bank Structure in Chicago, Illinois, www.federalreserve.gov. May 5, 2005.