[…] let us use the term "acceptable" to refer to utterances that are perfectly natural and immediately comprehensible without paper-and-pencil analysis, and in no way bizarre or outlandish [...] The more acceptable sentences are those that are more likely to be produced, more easily understood, less clumsy, and in some sense more natural [...] The notion "acceptable" is not to be confused with "grammatical". Acceptability is a concept that belongs to the study of performance, whereas grammaticalness belongs to the study of competence.
- Chomsky (1969), Pag. 10-11