  Tomasello's theory differs from a Chomskyan approach in three  important respects. First, and taking up a point mentioned in the  previous section, it employs a different conception of linguistic  competence, the end state of the learning process. Rather than  thinking of competent speakers as representing the rules of grammar  in the maximally abstract, simple and elegant format devised by  generative linguists, Tomasello conceives of them as employing rules  at a variety of different levels of abstraction, and, importantly, as employing rules that are not formulated in purely syntactic terms. He adopts a different type of grammar, called  ‘cognitive-functional grammar’ or ‘usage-based  grammar,’ in which rules are stated partly in terms of  syntactic categories, but also in semantic terms, that is, in terms  of their patterns of use and communicative function. A second respect in which Tomasello's approach differs from that of most theorists in  the Chomskyan tradition, is in employing a much richer conception of  the ‘primary linguistic data,’ or pld. For  generative linguists, the pld comprises a set of sentences,  perhaps subject to some preliminary syntactic analysis, and the child learning grammar is thought of as embodying a function which maps  that set of sentences onto the generative grammar for her language.  On Tomasello's conception, the pld includes not just a set  of sentences, but also facts about how sentences are used by speakers to fulfill their communicative intentions. On his view, semantic and  contextual information is also used by children for the purposes of  acquiring grammatical knowledge.