The thesis is a continuation of studies of Japanese modality, however its theme is not defined based on a particular kind of modality as is commonly done in synchronic studies but based on completely or to a degree shared common origin of the studied forms. Usage and properties of Early Middle Japanese -m.u are compared with usage and properties of Modern Japanese {-ō /-jō} a darō, schematic meanings of respective forms are suggested and grammaticalization and subjectification shifts which have taken place during approximately one thousand years of development are mapped. The results of the analysis show that subjectification has taken place and that the main impuls leading to the subjectification changes was grammaticalization of suffix -m.u to ending {-ō /-jō} respectively to particle (in Narrog (1998) terms) darō, which lead to split of one schematic meanings "inclination" in general control cycle (Langacker 2002, 2009) to two separate schematic meanings "inclination" in factual respectively epistemic control cycle. Powered by TCPDF (www.tcpdf.org)