The human capacity for language is one of the most contentious topics in cognitive science. While some researchers attribute language to domain-general mechanisms, others postulate a specialized language system. When it comes to the phonological component, however, even proponents of domain-specificity concede that specialization is unlikely (Fitch et al., 2005). Phonological competence, in this view, is the product of experience, auditory perception, and motor control. And indeed, phonological systems are intimately grounded in phonetics. But while the domain-general perspective can account for this fact, it offers no explanation for several key features of language. It fails to explain why all languages—signed and spoken—have a phonological system, why phonological systems emerge spontaneously, in the absence of a model, and why the cultural invention of reading and writing invariably recapitulates phonological principles. Such observations, however, are readily explained by the view of phonology as a core knowledge system.