This article suggests evidence for and reasons why prior acquisition may either facilitate or inhibit acquisition of a new construction. It investigates acquisition of the German passive and future constructions which contain a lexical verb with either the auxiliary sein “to be” or werden “to become”, and are related through these to potential supporting constructions. We predicted that a supported construction should be acquired earlier, faster, and unusually rapidly. An inhibited construction should show an extended depressed usage. We analyzed a (...) dense corpus of a German boy between 2;0 and 5;0. He acquired the sein- before the werden-passive. The former was supported by his prior acquisition of the sein copula, whereas the werden-passive itself supported one werden copula construction. He acquired the werden-future extremely slowly due to the hindrance of a semantically identical construction. These results fit with an emergentist approach in which apparently “sudden” acquisition is still due to gradual learning mechanisms. (shrink)