Although based on a logo-syllabic prototype, all vowels but short /a/ are written and so the system is essentially an alphabet. There are three vowels, long and short. Initially, no distinction is made for length: "a" or "ā," "i" or "ī," "u" or "ū." However, as in the Brahmic scripts, short "a" is not written after a consonant: "h" or "ha," "hā," "hi" or "hī," "hu" or "hū." (Old Persian is not considered an abugida because vowels are represented as full letters.)