This paper focuses on the history of a polyfunctional case marker 𗗙 jij1
in Tangut, an extinct Rgyalrongic language (Sino-Tibetan). This versatile case morpheme is a typological rarity of maximum syncretism among several abstract case functions, including differential object marking, the genitive, and the oblique (which overlaps with the dative). For one thing, accusatives originating from datives or spatial sources are rarely found with additional genitive functions; for another, reported instances of accusative/genitive syncretism seldom include other functions. The principal hypothesis of this paper is that the Tangut 𗗙 jij1
may be the result of multiple grammaticalization processes stemming from a proto-locative source. These processes can be subsumed under two pathways, one leading from an allative to an accusative, with an intermediate oblique stage, and the other from a locative to a genitive. Although both of these development pathways are frequently attested, the Tangut 𗗙 jij1
remains a typological rarity due to their superposition.