Om is written as a single syllable and analysed as three sounds: A, U, M. The Mandukya Upanishad, twelve verses long and the shortest of the principal Upanishads, maps each onto a state of consciousness. A is the waking state, produced at the back of the open mouth, the broadest sound. U is the dream state, rolling forward as the mouth narrows. M is deep sleep, the mouth closed, the sound resonant and internal. The syllable is a compressed map of everything you experience.
The fourth part is where the teaching turns. After M there is silence, and the Upanishad names this amatra, the measureless, without parts, corresponding to Turiya. It is not a fourth sound appended to the other three; it is what the three occur in and return to. The syllable is constructed so that pronouncing it correctly enacts the doctrine, moving from the widest opening to complete closure and then into what has no measure at all.
This is why the recitation instructions are so specific about the ending. The syllable is not stopped; it is allowed to thin out until the practitioner cannot say where the sound ceased, and attention is held in what remains. The tradition treats the silence as the real content and the three sounds as the approach to it. Everything the texts say about the fourth state, about the witness, about what cannot be described, is folded into an instruction about how to finish saying one syllable.
Om is a doctrine you can pronounce, and its most important part makes no sound. To see the state its silence points at, explore more of The Living Sanatan Timeline.
Part 18 of 100 — Series I: From the Beginning
Series I: From the BeginningThe Five KoshasIndexFAQThe Timeline