Demand: Vital and Non-Vital

Demand can be divided into vital need and non-vital want.  Correspondingly, other Economic categories can be likewise divided--Use-Value, Utility, Supply, etc.  Conversely, that the division is not recognized is reflected e. g. where the Demand for Viagra and the Demand for heart medication are indifferently ascribed to a 'Consumer'.  So, one example of a Prescriptive Economics formulation that is not to be found in a Descriptive Economics is the principle that distinguishes vital from non-vital Demand, and sets the universal meeting of it as a priority.