  To formalize this, we consider an arbitrary date \(t\) at which DM is deliberating. Let \(\tau\) denote dates not earlier than \(t\) (i.e., \(\tau \ge t)\). Ramsey considered a deterministic, infinitely lived world (but see Yaari, 1965, for the first of many extensions of the Ramsey model that incorporate the risk of individual or societal extinction). Well-being is assumed to be a numerical quantity. Let \(U(t)\) be well-being at \(t\), and let \(V(t)\) be an aggregate measure of the flow of well-being across time and generations, as evaluated at time \(t\). Ramsey followed Sidgwick in assuming that