I am engaged in a study of historical changes in the phonemes and grammar of the Japanese language from the Nara period (8th century) to the present day. My recent research focuses on elucidating ancient Japanese language in the period before recorded history by analyzing 8th century Japanese literature. I have already succeeded in partially identifying a system of verb conjugation which existed circa 1BC/1AD. My theory that there were only two types of verb conjugation at that time, called the kamiichidan katsuyo (upper single grade) and shimo-ichidan katsuyo (lower single grade) is contrary to the commonly-held view, which is based on a form of conjugation called the yodan katsuyo (quadrigrade). The theory has not yet been widely recognized by conservative academic circles.