The Seed Syllable 'a'

"The letter 'a' is the first letter of the Indic alphabets. It is the short 'a' sound that we find in the English word but (= ə in the IPA Alphabet). In Indic languages each consonant has an implied short a attached to it, so the consonants are ka, kha, ga, gha, etc. So 'a' is said to be present in each consonant, and to be the mother of all of the letters. If you open your mouth and breath out the sound is 'a'."

http://www.visiblemantra.org/a.html