Vowels following a consonant are inherent or written by diacritics, but initial vowels have dedicated letters. There are three "primary" vowels in Ashokan Brahmi, which each occur in length-contrasted forms: /a/, /i/, /u/; long vowels are derived from the letters for short vowels. There are also four "secondary" vowels that do not have the long-short contrast, /e/, /ai/, /o/, /au/.[25] Note though that the grapheme for /ai/ is derivative from /e/ in a way which parallels the short-long contrast of the primary vowels.