This paper develops a continuous variant of the theory of social custom of akerlof (q. J. Econom. 94 (1980) 749) to model the impact of a traditional household norm on married women's labour supply. The erosion of this norm is treated as the endogenous result of feedback of the labour supply behaviour on the norm beliefs. These endogenous dynamics are shown to imply multiple long-run equilibria on both the individual and collective levels exhibiting hysteresis and mutual transitions dependent on the wage rate. It is suggested that these properties have played important roles in the long-run increase in married women's labour supply in many oecd countries.