ཨ་ཡིག་དབྱེ་བ་བརྒྱད།

Tibetan grammarians (bSod-nams-rtse-mo and Sa-paṇ) speak of eight kinds of a:

(a) “inexpressible three [types of] a” (brjod du med pa’i a gsum):
1. bar tsheg srog gi a = yi ge so so’i bar du ’jug pa (i.e. inherent a accompanying each syllable)
2. dang kyog gi a = dbu khyud = dang por ’jug pa glang po che’i sna lta bu (i.e. heading a)
3. shad kyi a = mtha’ mar ’jug pa rnam par gcod pa (i.e. visarga)
(b) yan lag gi a = 4 = i, u, e, and o
(c) rtsa ba’i dbye gzhi’i a (i.e. a, which is the basis of all)

See the Thon mi’i zhal lung (pp. 68–72).