AbstractThis paper serves two purposes. It is a summary of much work concerning One compelling kind of evidence for the autonomy of a language’s morphology is the incidence of inflectional polyfunctionality, the systematic use of the same morphology to express distinct but related morphosyntactic content. Polyfunctionality is more complex than mere homophony. It can, in fact, arise in a number of ways: as an effect of rule invitation (wherein the same rule of exponence serves more than one function by interacting with other rules in more than one way), as an expression of morphosyntactic referral, as the effect of a rule of exponence realizing either a disjunction of property sets or a morphomic property set, or as the reflection of a morphosyntactic property set’s cross-categorial versatility. I distinguish these different sources of polyfunctionality in a formally precise way. It is inaccurate to see polyfunctionality as an ambiguating source of grammatical complexity; on the contrary, by enhancing the predictability of a language’s morphology, it may well enhance both the memorability of complex inflected forms and the ease with which they are processed.