Due to these extra syllables, it has been hypothesized that Old Japanese's vowel system was larger than that of Modern Japanese – it perhaps contained up to eight vowels. According to Shinkichi Hashimoto, the extra syllables in Man'yōgana derive from differences between the vowels of the syllables in question. These differences would indicate that Old Japanese had an eight-vowel system, in contrast to the five vowels of later Japanese. The vowel system would have to have shrunk some time between these texts and the invention of the "kana" ("hiragana" and "katakana") in the early 9th century. According to this view, the eight-vowel system of ancient Japanese would resemble that of the Uralic and Altaic language families. However, it is not fully certain that the alternation between syllables necessarily reflects a difference in the vowels rather than the consonants – at the moment, the only undisputed fact is that they are different syllables. A newer reconstruction of ancient Japanese shows striking similarities with Southeast-Asian languages, especially with Austronesian languages.