[…] a distinction must be made between the 'conventions' [...] and the 'syntactic redundancy rules' [...] The former are universal, and therefore need no specific statement in the grammar. They are part of the procedure for interpreting grammars [...] The latter, on the other hand, are particular to a given language, and therefore must be given in the grammar. I have tried to emphasize this by calling the former "conventions", and the latter "rules".
- Chomsky (1969), a pag.168