This paper presents a simple model of legal dualism in which a pro-poor legal reform, under certain conditions, causes the conflicting custom to go some way toward producing the change intended by the legislator. As a result, even if the formal law is not resorted to in an explicit manner, its mere existence might create a situation in which its objectives are partly met. This is illustrated with examples on inheritance, marriage, and divorce issues in Sub-Saharan Africa and India. The conditions under which a moderate pro-poor reform is more effective than a radical reform are also characterized in this paper.