In contrast to the "co-operative" economy of classical theory, the "entrepreneur" economy described by Keynes' general theory can achieve not only market clearing as a possible outcome but also stagnation and instability. There is an aspect of common cause between Keynes and Marx. Specifically, the rhetorical task of persuading political economists to rethink capitalism's inherent stability requires a refutation of classical theory's thin concepts of money and the magnetized nature of capitalist production.