The subject of this study is the case category system of Ket language, the only existing language of the Yeniseian languages. After examining the usage of each case and case marker, we analyzed the singular/plural category, male/non-male category, animate/inanimate binary confrontation structure, which are important standards for the classification of cases of Ket language.
 Ket nouns are first classified into singular and plural, and if singular, they are classified into male/non-male categories, and if plural, they are classified into animate/inanimate categories. The three gender categories for nouns, which are male, female, and neutral, cannot be seen as a morphological difference in nominatives. Gender categories only play a dominant role in genetive case and dative, ablative, benefactive and adessive cases, which are made in basis of genetive case.
 It was found that it is reasonable to view the dative, ablative, benefactive, and adessive, which have binary structure according to male/non-male and animate/inanimate, as a declinable case. Locative, instrumental, abessive and prosecutive have no distinction between male/non-male, animate/inanimate, and they do not change according to the number and gender, so the case markers for these nouns are similar to case suffixes or propositions. As for the vocative, it has a male/female binary structure in singular, but they don’t have any confrontation structure in plural, which is very different from other standards.
 As such, the Ket language system does not have a clear system that appears in Indo-European languages due to the correlation between the confrontational structure of the class, the hierarchy of the class, and the postposition. So the Yeniseian language case system should be viewed as a binary structure, which has a declinable group(nominative, genetive, dative, ablative, benefactive, adessive, vocative) and indeclinable group(locative, instumental, prosecutive, abessive).
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