Michael Perelman has unearthed the work on obsolescence of David Wells and Edward Atkinson, "scooping" Schumpeter by many years. Let me suggest that perhaps all these writers unbalanced the scene by romanticizing the entrepreneur and/or inventor too much. There are many quotidian causes and kinds of obsolescence. Energy costs may rise; fashions change; building codes change; auto use grows, crowding small lots; ground rents rise; population grows; wages of domestic help rise; cities expand; electrical appliance uses grow, obsoleting old wiring because higher capacity is needed; fickle demands change; etc. Of all those I would suggest more focus on locational obsolescence, as cities evolve, business districts migrate, etc. The need to salvage old sites for new uses is a powerful force for "creative destruction". Otherwise, old structures would stand for generations until natural forces destroy them, like the old barns and abandoned buildings one still sees in rural areas. Mason Gaffney