The datival genitive, the most common occurrences of which (e.g. Andacat sis ne Keisarin iotca Keisarin ouat ‘render therefore unto Caesar the things which are Caesar’s’) are found in 16^th century written texts, has been one of the most absorbing puzzles in diachronic research on Finnish. It has even been thought to be of Proto-Uralic origin, but no credible traces of it have been found in the languages related to Finnish. The present study aims to explain the origin of the Finnish datival genitive within the reference frame of the historical-comparative method.

The point of departure of the present study is the Finnish datival genitive. It is then compared to the dative in Livonian and to the genitive in possessive clauses in South Saami, Mordvin and Mari, which were previously thought to be connected to the datival genitive. On the basis of a description of the Finnish datival genitive, these cases are portrayed and examined on a language-by-language basis using a comparative method based on case syntax and taking the means of expressing possessive relations into account. The possible influence of foreign languages has also been investigated through an analysis of the occurrences of the verbs giva ‘give’ and säga ‘say’ in Early Modern Swedish and Old Swedish. The material consists of texts and electronic corpora of the target languages, and approximately 10 000 sentences have been analysed.

                      The result of this comparative analysis is consistent with previous studies and shows that there are no traces of the datival genitive in related languages; i.e. the datival genitive could either have completely disappeared from these languages or is a relatively late innovation in Finnish. The last alternative is supported by an account given of the indirect objects of the verbs giva ‘give’ and säga ‘say’ in Early Modern Swedish and Old Swedish which explains the puzzling restricted occurrence of the datival genitive. This in turn supports the postulation that the datival genitive is a morphosyntactic fossil in Finnish mirroring changes occurring in the Swedish case system between the Late Old Swedish of the 1450s and the Early Modern Swedish of the beginning of the 1500s.