Demand and supply of “Empty sum”

T. C. A. Srinivasa-Raghavan asks how the causality function? And “f, say, the demand curve for something shifts upwards, how do you know which of the following caused it: an upward shift in per capita incomes, a change in tastes and preferences, or simply a generational change?

Economists, with their certitudes, often carry on as if they know for sure. The truth, however, is that there is simply no way of telling”.