Japanese evidential mitai originated from the construction omitayoo which emerged in late Early Modern Japanese. After dropping the accusative marker and phonetic erosion, omitayoo evolved into mitai around 1880. The two forms coexisted for a few decades until the 1940s when omitayoo was completely replaced by mitai. In the 1930s, mitai developed evidential functions, primarily inferential, out of simile and acquired the use of euphemism. The formal change of mitai in the process of acquiring evidential functions runs counter to the unidirectionality hypothesis of grammaticalization, but the functional change conforms to the criteria of subjectification. During the second half of the 20th century, independent use as an affirmative appeared and a change of pitch accent pattern towards prosodic independence also took place.