Core-grammar is that part of the relatively stable (steady) state of the language faculty (i.e. of the adult I-language) that results from the setting of parameters in UG (the initial state of the language faculty, S0).
As opposed to the periphery, which consists of additional, marked, language-specific rules and exceptions.
- Chomsky, Noam A. 1986. Knowledge of language: its nature, origin and use. Praeger, New York.