This paper takes a typological approach to the case marking on subjects and objects in Estonian. The aim of the study is to establish whether case marking can be seen as a straightforward indicator of definiteness in Estonian grammatical relations. The discussion is based on the Transitivity Hypothesis put forward by Hopper & Thompson (1980). Hopper and Thompson see transitivity as a cover term for various characteristics of a clause that specify its degree of effectiveness.
The current paper illustrates that the Transitivity Hypothesis in broad terms is able to account for the case variation of Estonian subjects and objects. It also shows that the hypothesis needs to make a more subtle distinction of possible noun phrases constituting the subject relation in terms of Individuation. In Hopper and Thompson’s theory this characteristics has been assigned to object arguments only. In conclusion, the current study states that in Estonian case marking reflects the transitivity of a clause, but is not a transparent indicator of grammatical relations.