This article approaches the origin of multilingual innovations in language contact by presenting data from an intensive contact situation between two closely related Finnic languages, Finnish and Estonian. This situation between languages that have complex interconnected morphological systems often leads to the emergence of structures that contain material from both languages. The origin of these structures is discussed in the light of two basic assumptions: that in the mind of the bilingual speaker, the elements of the two languages are connected to each other via phonological and semantic or functional similarities and that both languages of the bilingual speaker always remain active and available during speech processing. The simultaneous activation of synonymous, competing elements or patterns is hypothesised to be the cause for the inevitable presence of both language-internal and cross-linguistic forces at the initial stage of language change.