This study presents a novel theory on the interaction of social norms, fertility, education, and their joint impact on long‐run economic development. The theory takes into account that sexual intercourse is utility enhancing and that the use of modern contraceptives potentially conflicts with prevailing social norms (religious beliefs). The theory motivates the existence of two steady states. At the traditional steady state, the economy stagnates, fertility is high, education is minimal, and the population sustains a norm according to which modern contraceptives are not used. At the modern steady state, the population has abandoned traditional beliefs, modern contraceptives are used, fertility is low and education and economic growth are high. Social dynamics explain why both equilibria are separated by a saddlepoint‐equilibrium (a separatrix), i.e. why it is so hard to transit from the traditional regime to the modern regime.