Word classes show different degrees of sensitivity and susceptibility both to contact induced language change (borrowing) and to language mixing in conversation (codeswitching). Our contribution addresses the hierarchical nature of word class arrangement as manifested in language contact settings. We review generalisations that have addressed the question of borrowing constraints on particular categories and examine some of the features that accompany the integration of borrowed items in particular word classes. We then examine some of the insights gained from the analysis of bilingual corpora and their implications for an explanatory model of borrowing and the status of word classes in contact-induced change.