The names of the fourth and sixth to ninth generations of emperors are obviously Japanese-style posthumous names, but according to reliable descriptions in "Kojiki" and "Nihon Shoki," Japanese-style posthumous names came to be used around the mid-sixth century; and although names like Jinmu and Suizei may sound like names of emperors used when they were alive, names that contain characters representing god (as in Jinmu) is unlikely to have been used as names of living persons, which leads us to believe that these were names for legendary characters or something similar to posthumous names and that, therefore, these emperors were added to the imperial lineage later in history.
4代・6代～9代の天皇の名は明らかに和風諡号と考えられるが、記紀のより確実な史料による限り、和風諡号の制度ができたのは6世紀半ばごろであるし、神武・綏靖のように、伝えられる名が実名であるとすると、それに「神」がつくのも考え難く、やはり神話的ないし和風諡号的なものであるので、これらの天皇は後世になって皇統に列せられたものと推定できる。