(1) I called up the man who wrote the book that you told me about [...] (2) I called the man who wrote the book that you told me about up [...]. 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. The sentences of (2) are low on the scale of acceptability but high on the scale of grammaticalness, in the technical sense of this term. That is, the generative rules of the language assign an interpretation to them in exactly the way in which they assign an interpretation to the somewhat more acceptable sentence of (1). Like acceptability, grammaticalness is, no doubt, a matter of degree, but the scale of grammaticalness and acceptability do not coincide. Grammaticalness is only one of many factors that interact to determine acceptability.
- Chomsky (1969), a pag.11