음성음운형태론연구 19집 1호 Kan Sasaki 

Sasaki, Kan. 2013. Another look at sa-insertion in Japanese. Studies in Phonetics,Phonology and Morphology 19.1. 179-190. 

The sa-inserted causative form is a substandard form of the causative predicate. For this phenomenon, there are two analyses, the suffix leveling analysis and the double causative analysis. The present paper advocates a third analysis, the stem leveling analysis, where sa-insertion results from treating the host for causative suffixation as the irrealis stem across the board. This analysis is compatible with all the range of sub-standard causative forms, including rarely mentioned irrealis based causative form of the s-irregular verb. (Sapporo Gakuin University)