tly, bilingual children's language mixing has often served as material for discussing whether children are able to develop two languages separately from an early period (two-system model) or a phase of temporary language mixing precedes differentiation as part of development (one-system model).
             There are variations in bilingual mixing, such as loan blends, syntactic mixing, semantic mixing, and pragmatic mixing. Each type of mixing seems to occur under different situations, probably for different reasons. For example, a bilingual child may use pragmatic mixing to capture a parent's attention by first using one language and if the parent has taken no notice after this tactic, then using the other language. In addition to variations in mixing, there are also variations in the rates of mixing from study to study. These results are difficult to analyze and compare since they occur under different situations with different languages for children with different language backgrounds. However, a trend that appears to hold true in most cases is that mixed utterances show higher frequency in the early stages of bilingual development and that this frequency diminishes with age (Genesee 1989).
             It is important to note that bilingual adults also sometimes combine two languages in a single sentence. Research indicates that this so-called code-mixing phenomena is an organized, "rule-governed communicative device" that is used by linguistically mature bilinguals "to achieve a variety of communicative goals" (Genesee 1989). A bilingual adult may, for instance, use code-mix for role playing purposes or to establish a socio-cultural identity. This phenomena, unlike in bilingual children's mixing, is highly structured, with syntactic and sociolinguistic constraints. Thus the belief is that what differentiates bilingual children's mixing from adults' mixing is "the lack of systematicity or compli...