  We now construct an informal version of the variational argument Ramsey used for determining \(\{C^*(t)\}\) in Mark III. Loosely speaking, the DMs require the marginal rate of ethically indifferent substitution between consumption at any two brief periods of time to equal the marginal rate at which consumption can be transformed between those same pair of brief periods of time. Their equality (i.e., the right balance from among the “desirables” and the “feasibles”) is a necessary property of an optimum consumption stream.