. ..a rather short list of semantic propositions and relations. . . will .encompass the nonlexical or compositional meanings [i.e., the underlying conceptualizations] of the majority of all multi-morpheme utterances produced by the Stage I children. . . . these meanings seem to represent linguistically the sensori-motor intelligence which develops, according to Piaget's research, in the 18 months or so which normally precede Stage I. (1973, p. 64)

The Stage I child realizes these conceptualizations in language in a direct way. Examples have already been given of how the three operations of reference (a-c) are realized. The seven semantic relations are realized in speech simply by replacing each element by a word that represents what is "playing" that semantic role. The order of the conceptualization is maintained. For example, in an utterance representing an agent + action conceptualization, the agent will always precede the action.

Even much more advanced children express their conceptualizations, and assume that others express theirs, in a fairly direct way. For example, children have difficulty in understanding reversible passive sentences, since they disrupt the expected agent action- object order; given the sentence "The girl was hit by the boy," children often incorrectly understand it to mean that the girl hit the boy (Slobin, 1966).

As the child advances, the "realization rules" become increasingly complex. By the time he reaches the adult stage, he has many possible ways of representing any conceptualization in language; there is no longer anything approximating a direct mapping between sentence and conceptualization (although, of course, the adult can use simple language, as he might when speaking to a young child). There are a great many mysteries with complex language, both on how to describe the realization rules and on how the child learns them.