Abstract One of the major goals of linguistics is to delineate the possible range of variation across languages. Recent work has identified a surprising number of typological gaps in a variety of domains. In morphology, this includes stem suppletion, person pronoun syncretism, case syncretism, and noun stem allomorphy. In morphosyntax, only a small number of all conceivable Person Case Constraints and Gender Case Constraints are found. While various proposals have been put forward for each individual domain, few attempts have been made to give a unified explanation of the limited typology across all domains. This paper presents a novel account that deliberately abstracts away from the usual details of grammatical description in order to provide a domain-agnostic explanation of the limits of typological variation. This is achieved by combining prominence hierarchies, e.g. for person and case, with mappings from those hierarchies to the relevant output forms. As the mappings are required to be monotonic, only a fraction of all conceivable patterns can be instantiated.