The term formal theories of language usually refers to linguistic theories that stem from the work of Noam Chomsky on Universal Grammar, or the idea that there is an innate language mechanism in humans that allows us to learn and use language. These theories are are also referred to as generative grammar, and are prominent in linguistic research in the United States. As a results, they have informed a great deal of research on second language acquisition, as well as theories of teaching. When the folk linguistic theories of language learning I discussed previously are contrasted with linguistic theories, these linguistic theories are most often formal theories. From my perspective, there are three main implications for taking an approach to language learning and teaching informed by formal theories of language, and I discuss these below.