The existence and meaning of this system is a critical point of scholarly debate in the study of the history of the Japanese language.
Those syllables marked in gray are known as jōdai tokushu kanazukai.
It predates the development of kana, and the phonetic difference is unclear.
One popular system places a diaeresis above the vowel: ï, ë, ö.
A word is consistently, without exception, written with syllables from a specific group.
This strict distinction exists for all of the syllables marked in gray.
Thus, its conjugation is as follows: Before the jōdai tokushu kanazukai discovery, it was thought that quadrigrade realis and imperative shared the same form: -e. However, after the discovery, it became clear that realis was -e2 while imperative was -e1.
As seen in early Heian Period texts such as Kogo Shūi, the final syllables to be distinguished were /ko1, go1/ and /ko2, go2/.