The monopoly power of private property

All rent, recall, is a return to the monopoly power of private ownership of some crucial asset, such as land or a patent. The monopoly power of private property is therefore both the beginning-point and the end-point of all capitalist activity. A non-tradable juridical right exists at the very foundation of all capitalist trade, making the option of non-trading (hoarding, withholding, miserly behavior) an important problem in capitalist markets. Pure market competition, free commodity exchange, and perfect market rationality are therefore rather rare and chronically unstable devices for coordinating production and consumption decisions. The problem is to keep economic relations competitive enough while sustaining the individual and class monopoly privileges of private property that are the foundation of capitalism as a political-economic system.

David Harvey, Rebel Cities (Verso, 2013) p. 94