This dissertation argues for the position that code-switching utterances are constrained by the same set of mechanisms as those which govern monolingual utterances. While this thesis is in line with more recent code-switching theories (e.g. Belazi et al. 1994, MacSwan 1997, Mahootian 1993), this dissertation differs from those works in making two specific claims: Firstly, functional categories and lexical categories exhibit different syntactic behaviour in code-switching. Secondly, codeswitching is subject to the same principles not only in syntax, but also in production and pragmatics. Chapter 2 presents a critical review of constraints and processing models previously proposed in the literature. It is suggested that in view of the vast variety of data, no existing model is completely adequate. Nevertheless, it is argued that a model which does not postulate syntactic constraints (along the lines of Mahootian 1993, MacSwan 1997) or production principles (along the lines of de Bot 1992) specific to code switching is to be preferred on cognitive and theoretical grounds. Chapter 3 concerns word order between lexical heads and their complements in code-switching. It is shown that the language of a lexical head (i.e. noun or verb) may or may not determine the word order of its complement. Chapter 4 investigates word order between functional heads and their complements in code-switching. Contrary to the case with lexical categories, the language of functional heads (e.g. D, I and C) is shown to determine the word order of their complements in code-switching. It is proposed that word order between heads (lexical or functional) and complements is governed by head-parameters, and the difference between lexical heads and functional heads is due to their differential processing and production in terms of Levelt's (1989) algorithm. Chapter 5 investigates the selection properties of functional categories in codeswitching, with special reference to Cantonese-English. Contrary to the Functional Head Constraint (Belazi et al. 1994), it is shown that code-switching can occur freely between functional heads and their complements, provided that the c-selection requirements of the functional heads are satisfied. Chapter 6 investigates the selection properties of lexical categories in code-switching, again with special reference to Cantonese-English. It is shown that "language-specific" c-selection properties need not be observed: a Cantonese verb may take an English DP whereas an English verb may take a Cantonese demonstrative phrase (DemP). Similar phenomena are drawn from other language-pairs involving a language with morphological case and a language without morphological case. The difference between functional categories and lexical categories in their selection properties is again explained in terms of the different production processes they undergo. Chapter 7 is devoted to prepositions which have been problematic in terms of their status as a functional category or a lexical category. Based on the behaviour of prepositions in code-switching, it is suggested that prepositions display a dual character. It is proposed that prepositions may well point to the fact that the conventional dichotomy between functional categories and lexical categories is not a primitive one in the lexicon. Chapter 8 looks at code-switching in a wider perspective. and explores the pragmatic determinants of code-switching in the light of Relevance Theory (Sperber and Wilson 1995). It is argued that many types of code-switching (e.g. repetitions, quotations, etc.) are motivated by the desire to optimize the "relevance" of a message, with "relevance" as defined in Relevance Theory
