Non-constant Returns,Pareto Optimality and Competitive Equilibrium

Competitive equilibrium is not Pareto optimal if returns to scale are not constant, except in special and accidental circumstances. This result is demonstrated using a classical production model; it holds quite generally and independently of all other sources of Pareto inefficiency, such as externalities, imperfect information and quantity constraints. It establishes a general and ubiquitous basis for critique of the 'invisible hand' ideology, which still dominates both the textbooks and wider reaches of social thought.