  Well-being at any given date is assumed to be a function solely of consumption at that date. We therefore write \(U(t) = U(C(t))\). Ramsey assumed that marginal well-being is positive (i.e., \(dU(C)/dC \gt 0)\) but diminishes with increasing consumption levels (i.e., \(d^2 U(C)/dC^2 \lt 0)\).  The latter property implies that \(U(C)\) is a strictly concave function. (Edgeworth, 1885, had routinized the idea that marginal well-being declines with increasing consumption.) Thus equation (2) can be written as