This section begins with a discussion of the standard views of the stage of two-word speech-pivot and open classes. However, we will note some weaknesses in this type of analysis, the most important of which is that it considers only the forms of the child's utterances, while neglecting the meanings. Therefore we then look at some of the recent work on the child's attempts to represent basic underlying conceptualizations by his speech. Next we briefly discuss the child's acquisition of various grammatical morpheme factors and inflections that "modulate" or further specify the meanings of his speech. We then go on to more advanced syntactic forms, using the stages in the acquisition of the rules for forming negative sentences as an example. Finally, we look briefly at an important but unanswered question: What processes might account for the acquisition of syntactic knowledge?
Pivot and Open Classes. Children's syntactic forms, especially those first attempts to put words together to form more complex utterances, have been extensively studied in recent years. The child's first structured utterances generally consist of two words; he produces forms such as "this toy" and "mommy eat." Braine (1963) and others (Miller and Ervin, 1964; Brown and Fraser, 1963) have proposed that the child divides words into two different classes. One is a small set of frequently occurring words; in the corpora of children's utterances on which this analysis was originally based, these words occurred only in combination with other words, and generally preceded them. This class, which includes such words (at least for some children) as see, get, bye-bye, more, and no, are called "pivot" (P) words. The second is a large set, each member of which appears infrequently. This set of "open" (0) words consists mainly of words that are nouns or verbs in adult English.
Braine (1963) thought that the majority of the child's sentences (ie., complete utterances) could then be characterized by a few simple "rewrite" rules: