  Let \(t \ge 0\) denote time. In Ramsey’s model there is no uncertainty (but see Levhari and Srinivasan, 1969, for one of the first of many extensions of the Ramsey model that incorporate uncertainty about future possibilities). The economy is endowed with a single, non-depreciating commodity that can be worked by labour to produce output at each date (Gale, 1967, and Brock, 1973, were among the first of many extensions of the Ramsey model that contain a heterogeneous collection of capital goods). The economy is assumed to be closed to international trade (opening the economy to trade involves only a minor extension to Ramsey’s model). That means some of the output can be invested so as to add to the commodity’s stock while the remainder can be consumed immediately. We call the stock of the commodity that serves to produce output, “capital.” The problem is then to find the optimum allocation of output at each date between consumption and investment.