Post Keynesian macrodynamic models make various assumptions about the normal rate of capacity utilization. Those rooted in the Classical and neo-Keynesian traditions assume the normal rate is fixed, whereas Kaleckian models treat it as a variable that is endogenous to the actual rate of capacity utilization. This paper contributes to the debate about the normal rate of capacity utilization by developing a model of strong or genuine hysteresis, in which firms make discrete decisions about the normal rate depending on the degree of uncertainty about demand conditions. An agent-based model based on empirical analysis of 25 sectors of the US economy is used to show that hysteresis can cause variation in the normal rate of capacity utilization within a subset of the range of observed variation in the actual capacity utilization rate. This suggests that the economy exhibits both constancy and (endogenous) variability in the normal rate of utilization over different ranges of variation in the actual rate. More broadly speaking, the genuine hysteresis model is shown to provide the basis for a synthesis of Post Keynesian macrodynamics that draws on both the Classical/neo-Keynesian and Kaleckian modeling traditions.