Demographic translation relates period and cohort summary measures. Traditionally applied to analyses of fertility, the translation concept is extended here to mortality and to all types of decrements with unimodal rates. Using the assumption of a time-constant age-proportional rate schedule, explicit, interpretable, and closed form translation relationships are derived for cases where, over time, the level of the rates varies sinusoidally or according to a cubic polynomial. The results show that the cohort measure translates to the period measure for a specified number of years later, with an adjustment for the nonlinearity over time. For cubic time trajectories, those adjustments tend to be modest. For sinusoidal fluctuations they are substantial, and depend on the ratio of the reproductive age range to the length of the cycle. Substantively, cohort measures are seen as translated period measures. To the extent that the age pattern of rates is constant over time, cohort measures lose any claim to theoretical primacy.