This study explores one of the structural aspects of code-switching (CS) in two typologically distant languages, English and Japanese. Only the ‘insertion’ type of CS is dealt with, since it entails grammatical interaction between the two languages. Data collected from a pair of English-Japanese bilingual siblings’ CS are analyzed using Myers-Scotton’s MLF and 4-M models (2002), which are insertion frameworks. Viewed from the perspective of EL activation, the study identifies a continuum from borrowing to single-item insertion, to multi-item insertion. The study also investigates whether the matrix language (ML) can be identified using the System Morpheme and Morpheme Order Principles. The combination of the two Principles works well when the EL activation level is low. However, the System Morpheme Principle does not work in cases where the EL is fully activated. Based on this study, it is suggested that the MLF model can be subsumed under the continuum-based model.
