Ths chapter introduces MacSwann’s (1999) model. It is a minimalist framework within separationist assumptions to the extent that it is claimed that the bilingual has two lexicons and two PFs. The chapter also presents two empirical challenges to this model: mixed selection and noun classes. Mixed selection refers to the empirical fact that an item from “one lexicon” may select for an item in “the other” lexicon. Under the label “noun classes,” I show that an English noun can be inserted into a Swahili discourse, in the process acquiring a noun class. Both these well-known features of code-switching are empirical problems for any theory that posits separate lexicons. The chapter ends with a brief discussion of Multiple Grammar Theory highlighting the points of contact and divergence with the integrationist approach.

This chapter makes an initial presentation of the 1Lex hypothesis. It is shown that the mixed selection and noun class puzzles disappear if there is only one lexicon. It is followed with a discussion of how the lexicon of a biingual must be organized and the possibility of competition at the vocabulary insertion point. It also explores some of the consequences of the hypothesis for our understanding of borrowing, loan translation, and syntactic transfer.