>It remains an
>intellectual exercise, which may excite mathematically inclined economists
>but is no substitute for economic analysis in which mathematics may serve
>for some purposes, as an aid to understanding, but never as a replica of
>real economic processes.
Keynes, in a letter to Harrod: "But it is of the essence of a model that one does not fill in real values for the variable functions. To do so would make it useless as a model. For as soon as this is done, the model loses its generality and its value as a mode of thought."