This volume is an extension of Optimality Theory to the study of Code Switching, the use of two languages with a sentence. Optimality Theory, a theory of constraint ranking and interaction, proves to be a promising framework in dealing with forms of language variation, which ohter conventional formalisms have had difficulty in accounting for fully.  Code Switching as an instance of synchronic variation can serve as a productive testing ground for such a model.

This present study focuses on Code Switching spoken by Hong Kong bilinguals, that is, the intermingling of English words or phrases within Cantonese sentences.  My analysis primarily centralises the notion of syntactic well-formedness of Code Switching from the perspective of Optimality Theory, for instance the examples of preposition-switching as the emergence of unmarked syntactic properties. My central objective is to contend that there are syntactic reasons for Code Switching, apart from metalinguistic ones which are already well-investigated.  In most cases, Code Switching is optionally selected as optimal along with single-language outputs sharing the same semantic interpretation. On other occasions, Code Switching may yield outputs which are actually more well-formed than those of single languages, according to the robust constraint-ranking mechanism of Optimality Theory.  This is consistent with the assumption that Optimality Theory strives for the best candidate regardless of the source of syntactic objects they are dealing with. The recourse to items of another language may facilitate the search for a more optimised form of utterance.  Such a result seems justifiable in that bilinguals have more lexical items available in their lexicons, and can switch items in order to maintain or even enhance well-formedness. Also a special chapter of A-not-A reduplication is presented in order to illustrate the interface between prosody and morphology, by means of the constraint-ranking mechanism in Optimality Theory.

On more conceptual grounds, the study of Code Switching offers fresh perspectives on how speakers design a new form of language.  As Code Switching looks into hte strategy bilinguals adopt so as to attain a higher level of optimailty, such tactics should be operative across languages and individuals. This work  reveals one facet of economisation of language, i.e. a switch of lexical items could obviate numerous algorithmic complexities which speakers might otherwise come across. In view of this, Code Switching provides a new way to solve this puzzle.