Say that you hire me to mow your lawn and afterwards you pay me $30. What I have earned might be thought of as certificates of performance, i. e. proof that I served you. With these certificates of performance in hand, I visit my grocer and demand 3 pounds of steak and a six-pack of beer that my fellow man produced. In effect, the grocer asks, "Williams, you're demanding that your fellow man, as ranchers and brewers, serve you; what did you do in turn to serve your fellow man?" I say, "I mowed my fellow man's lawn." The grocer says, "Prove it!" That's when I hand over my certificates of performance — the $30.

Markets, Governments, and the Common Good, speech at Hillsdale College, 27 September 2007