Abstract. A probabilistic grammar approach to language assumes that grammatical knowledge has a probabilistic component and that this probabilistic knowledge of language is derived from language experience. It is assumed that the extent and nature of grammatical knowledge is reflected in language variation. In the present paper, the probabilistic variation patterns of the Estonian exterior locative cases and the corresponding postpositions are determined by exploring a large, manually annotated dataset of Estonian web texts. It is proposed that there are both similarities and differences in the morphosyntactic knowledge on the part of Estonian speakers as pertains to the three alternations: allative ~ peale ‘onto’, adessive ~ peal ‘on’, abl...