This paper is concerned with problems of learnability. It speculates on how learners, with the help of UG and a few common-sense strategies, go about discovering abstract relationships between superficially different structural formats available in the input. Far from being confused by variation, learners can use what they perceive as conflicts between UG and experience to infer new system properties. According to the multiple-roots perspective proposed here, the monolingual child starts out like a bilingual child, that is, with coexisting (but not arbitrary) sentential roots, eventually deciding where convergence is possible and where (as in the case of the real bilingual) it is not. The knowledge domain for which this scenario is explored is the acquisition of finite and nonfinite verb placement in German. The paper also addresses the issue of how different target languages enhance or slow down the overall process of structure building and relates this to asynchronies observed in bilingual children.