Causes of Monopoly: This section discusses some of the sources of monopoly power.  It is important for students to realize the sources of monopoly power and the measurement of monopoly power (e.g. using the Lerner Index as described earlier) are two different things.  It is also useful to link the discussion here of cost-based sources of monopoly power back to the chapters on production and cost to remind students that some of the cases of monopoly are simply a consequence of underlying economic conditions.  This is important both now and later, since some of the sources of monopoly power (government action, strategic decisions by the firm, possibly illegal actions) are decidedly not inevitable the same way that scale economies may be.