 Much of the development of the models in the literature was grounded in a set of post-war "stylized facts" that every economics Ph.D. student learns in their first year of graduate study.One of the weak links in the development of these early models was their specification of saving behavior as being exogenous and given by the empirical regularity of the consumption-income relationship, and the various (partial equilibrium) theories of consumption spending designed to explain this regularity.Cass's paper was the first to endogenize the consumption-savings decision by deriving an optimal capital accumulation trajectory that maximized the discounted sum of utility payoffs over time.