Historical Context

By the early 1960s growth theorists had two pieces on the board: Solow's exogenous-savings model (1956) and the resurrected Ramsey framework that Cass and Koopmans were independently developing. Both depended on a representative-agent abstraction that some economists found uncomfortable. The world is not populated by immortal households; it is populated by overlapping cohorts of finite-lived agents.

Paul Samuelson had already sketched the alternative in his 1958 *Journal of Political Economy* paper, *An Exact Consumption-Loan Model of Interest with or without the Social Contrivance of Money*. Samuelson's setting had no production — only an endowment economy with two-period agents — but it established the crucial insight: with overlapping generations and no asset to transfer wealth across cohorts, the autarkic equilibrium can be Pareto-inferior to alternatives sustained by money or social transfers.

Peter Diamond's 1965 *American Economic Review* paper, *National Debt in a Neoclassical Growth Model*, took Samuelson's two-period structure and added capital and production. The result was a complete general-equilibrium growth model with a non-trivial role for government debt. Diamond showed that issuing public debt in a dynamically inefficient economy could raise welfare by crowding out excess capital — an idea that would later become central to the debate over Social Security in the United States.