本文主要探討賽德克語時式（貌）助動詞之語法化，並主張其動詞musa 「去 主事」與 maha 「去 主事」為同源詞；兩者共存之原因乃為動詞*muSa 因 maha 語法化為標示未來之助動詞而一分為二的結果。賽德克語musa 與 maha 同源顯示在泰雅古語（Proto-Atayalic）甚或南島古語（PAN）可能曾經存在*S > s與*S > h 之音變競爭, 此一發現有其歷史意義。

The purpose of this paper is two-fold. It aims at a general exploration of the auxiliaries that mark tense/aspect in Seediq from a grammaticalization perspective on the one hand, and on the other hand, argues that the future-marking auxiliary maha and the verb musa ‘to go AF’ are cognates. The co-existence of maha and musa is the result of a split of the verb *muSa due to the grammaticalization of maha as an auxiliary to mark futurity. The finding that Seediq musa and maha are cognate with the PAN *kuSa ‘to go’ implies that a competition change between *S > s and *S > h might have occurred in the Proto-Atayalic as well as in the PAN, a finding that is historically significant.