Second language acquisition (SLA) research arose from the developments of the proposals made by Chomsky (1965) regarding the concept of The Language Acquisition Device (LAD), a language faculty that enables children to infer hypotheses about the rules of a certain language given that they are exposed to a considerable amount of linguistic input. Furthermore, Chomsky suggested that all languages are structured according to a set of universal principles; then, it is assumed that children have an innate knowledge of these universal principles which enables them to acquire the native language quickly, easily and efficiently. Added to these ideas, Chomsky’s mentalist theory of language acquisition contains the concept of linguistic competence, which consists in the mental representations of linguistic rules that constitute the speaker-hearer’s internal grammar, and linguistic performance, realized through the use of this grammar in the comprehension and production of language. Although Chomsky’s theory was developed within the field of the acquisition of the mother tongue (also known as L1), it had an effect on SLA theories since it showed that the acquisition of a given language could not be explained in terms of habits or imitation as the behaviorist view stated. When applying Chomsky’s proposals to the learning of a second language (L2), the differences between languages are not relevant issues to be considered in such process. Hymes (1971) extended the distinction of the concepts of linguistic competence and linguistic performance to include the communicative aspects of language, i.e. to cover linguistic and pragmatic knowledge. As a result, nowadays, SLA aims at the description and explanation of the learners’ linguistic or communicative competence by examining their performance.