mantras and sacred sound
What is the Vishnu mantra 'Om Namo Narayanaya' and how does it differ from the Ashtakshara?
The two mantras
The Dvadashakshara means 'twelve-syllable.' When you count the syllables in Om Namo Narayanaya, you get twelve. This mantra names Narayana, one of the central names of Vishnu, and the words carry the sense of bowing to him or taking refuge in him. The Ashtakshara means 'eight-syllable.' It is Namo Narayanaya, the same phrase without Om at the front, giving eight syllables. Some traditions treat these as two separate mantras with different standing. Others see the Dvadashakshara as the fuller form and the Ashtakshara as the inner core within it.
Where they come from
Both mantras are closely tied to the Pancharatra tradition, a body of texts and ritual practice devoted to Vishnu. The Narada Pancharatra and related texts give these mantras a central place. In Sri Vaishnava practice especially, these mantras carry great weight. The tradition holds that the Ashtakshara in particular is a mantra received through initiation, called diksha, from a qualified teacher. There are eligibility distinctions in some lineages about who receives which form and under what conditions. These rules vary between communities and teachers.
What the syllables mean
In the tradition, Om is the primal sound, pointing to the absolute. Namas carries the sense of surrender or offering of the self. Narayanaya means 'to Narayana,' the one in whom all beings rest, or the one who is the resting place of all. Together the mantra is understood as a complete act of surrender to Vishnu. The tradition holds that each syllable carries meaning and that the mantra works as a whole, not just as words.
A common point of confusion
People sometimes ask whether Om Namo Narayanaya is the same as Om Namo Bhagavate Vasudevaya. They are not the same. Om Namo Bhagavate Vasudevaya is a twelve-syllable mantra of Krishna as Vasudeva and comes from a different textual background. All three mantras are widely chanted today, but they belong to different streams of devotion. In everyday use, many people chant Om Namo Narayanaya simply as a name of Vishnu without the formal initiation context. Whether the stricter rules of eligibility apply is something different communities answer differently.