We have argued throughout this book that the cognitive system underlying a person's language capacity has intrinsic properties which are there by biological endowment. Those properties interact with contingencies resulting from exposure to a particular linguistic environment and the interaction yields a final state in which the person may communicate, perhaps some form of French. In that case, the person, Brigitte, will have incorporated from her environment the contingent lexical properties that livre is a word to refer to the novel she is reading and cooccurs with forms like le and bon (being “masculine”), père may refer to her father. She has also incorporated contingent structural properties: interrogative phrases like quel livre may be displaced to utterance-initial position, verbs raise to a higher functional position, and so on. We have described ways in which linguists have teased apart the intrinsic properties common to the species and the contingent properties resulting from individual experience. That work has been guided by the kind of poverty-of-stimulus arguments that we have discussed, by theoretical notions of economy and elegance, and by the specific phenomena manifested by the mature grammar under investigation.

Viewing a person's language capacity in this way and focusing on what we have called I-language leads one to ask novel questions about children and their linguistic development. The perspective we have sketched has already led to productive research and we have learned a great deal about the linguistic minds of young children.