How much knowledge of language is innate and how much is learned through experience? The nativist view endorses that human language acquisition is guided by innate rules ("Universal Grammar"), while the empiricist view assumes that language acquisition is the product of abstractions from stored exemplars. Despite the apparent opposition between these views, the essence of the debate lies in the relative contribution of prior knowledge and linguistic experience. The main goal is then to establish the minimal prior knowledge needed for language acquisition to take place. In this paper we will focus on a couple of hard linguistic phenomena that have for a long time been considered "parade cases of an innate constraint": auxiliary fronting and ...