1. Competence and Performance
1.1. Competence
Competence refers to a person's internalised grammar (knowledge) of his language. This means a native speaker's ability to produce and understand sentences, including sentences they have never heard before. It also includes a person's knowledge of what are and what are not sentences of a particular language. So, it is the code which underlies all utterances in a given language. A speaker's linguistic competence enables him to produce only grammatical and well-pronounced sentences, and to avoid the generation of ungrammatical and mispronounced sentences, and to recognise whether sentences are synonymous, ambiguous, simple, complex, etc. For Chomsky, linguistics should be concerned with competence. The latter is purely linguistic.
This is similar to Saussure's concept of langue, but Saussure stressed the social aspect of langue (the collective shared knowledge), whereas Chomsky stressed the individual nature of competence: He sees it as a set of processes possessed by the individual and developed in him as part of his maturation. “Langue” is extracted from utterances after they were produced, but “competence” is the system which creates sentences never heard before.