I begin by examining the inadequacy of the Cobb-Douglas model for studying evolutions over the very long run. Over a very long period of time, the elasticity of substitution between capital and labor seems to have been greater than one: an increase in the capital/income ratio β seems to have led to a slight increase in α, capital’s share of national income, and vice versa. Intuitively, this corresponds to a situation in which there are many different uses for capital in the long run.
