  The linear technology (eq. 11a) and the iso-elastic \(U\)-function (eq. 11b) allowed us to recognise immediately that if a consumption stream satisfying the Ramsey Rule is to be the optimum, both capital and consumption should grow at the same exponential rate, \(m\). Identifying a sufficient condition for optimality in more general models is a lot more difficult. What we need is a condition on the long-run features of a consumption stream satisfying the Ramsey Rule that can ensure it is the optimum. von Weizsacker (1965) showed that the required condition relates to the long-run behaviour of the social value of capital associated with that consumption stream. We now formalize the condition.