arapacana is made up of the first five syllables of an alphabet which occurs in the Perfection of Wisdom in 25,000 lines - translated by Edward Conze as The Large Sutra on Perfect Wisdom. I need to clarify 'alphabet' a bit. Actually Sanskrit is a syllabic language, which means that a consonant is almost always associated with a vowel. The most basic, unmarked, form assumes the short 'a' vowel sound which you hear in the English word but. That's why the 'alphabet' is not written in roman characters as arpcn! So this alphabet is spelt out in the Sutra, and each syllable is associated with some aspect of perfect wisdom. A, for instance, stands for anutpada - unarisen - and refers to the idea that no actual 'things' ultimately exist, that there are just conglomerations of conditions which are constantly changing. One of the most important conditions being our perception and the associated mental processes.
The alert amongst you will already have clocked that the Sanskrit alphabet does not begin a ra pa ca na - it begins with the vowels a, i, u, e, o, etc, in their short and long forms. Even the consonants start with ka, kha, ga, gha, nga, etc. So this is not the Sanskrit alphabet. Some scholars have postulated a Gandhari origin, or that it relates to the Karoshthi alphabet.* The earlier Lalitavistara Sutra also has an alphabet of Wisdom - this one is Sanskrit.
But why? What is special about the alphabet? The answer lies, I suggest, not in Buddhism at all but in one branch of Vedic exegesis known as Mimamsa (miimaa.msaa) which has origins almost as old as the Vedas themselves, although the first systematic account was Jaimini's Mimamsa Sutra probably written about 200 BCE - about a century before the Lalitavistara Sutra.
The central concern of the Mimamsa School was the status of the Vedas as divine revelation - and as such they parallel the Christian philosophers who sought to "prove" the divine status of the Christian Bible. The Indian problem was that the words used in the Vedas were (more or less ) the same words that ordinary people use in their banal conversations. What is so holy about them? A contemporary school, the Sphotavada, worked along the lines that the words were special because of the order that they were in - that it was the sentences of the Vedas that made them holy. The Mimamsa went in the other direction. The meaning of a sentence depends on the sum of the parts that make it up. The smallest units are what are true or real (both translations of satya) and in the case of Sanskrit this is the syllable. To quote Shabara, a mid-1st century BCE Mimamsa scholar:
"The word gauh (cow) is nothing more that the three phonemes which are found in it, namely g, au, and h... It is also these very phonemes which cause the understanding of the meaning of the word".Contemporary scholar Guy Beck adds:
"The human process of comprehension is therein said to result from the mysterious accumulation of individual letter potencies (shakti), each of which leaves an impression or trace (samskara), which carries over onto the next letter or syllable".**The early Upanishads contain several little treatises on the associations of syllables with esoteric meaning - Chandogya 1.3.6 for instance. But Shabara has taken this to it's logical conclusion and given significance to all of the syllables. This doesn't entirely solve the problem of logically establishing the revealed nature of the Vedas, but that need not distract us at present since that is not our project.
Shabara wrote in the time immediately preceding, or even slightly over-lapping, the rise of the Mahayana. We know that Buddhists, in accordance with the general Indian approach, were apt to incorporate any practice or idea which could be adapted to their use. It seems to me that in this case the Vedic linguistic speculations were adopted, and developed. The apotheosis of this occurs in the Mahavairocana Abhisambodhi Tantra where visualisation of the Sanskrit alphabet is recommended as a meditation practice.
It is interesting to note that this ancient India interest in the significance of words or syllables prefigures much of modern linguistics. Ferdinand de Saussure himself had held a professorship in Sanskrit before giving his lectures on general linguistics in 1910-11 that have set the agenda of linguistics ever since. Another interest contemporary parallel is in the research of Margaret Magnus. Magnus's doctoral thesis explored the way that phonemes (the smallest unit of articulate vocal sounds) bear meaning. Standard linguistic theory tells us that phonemes have an arbitrary relationship to meaning - that the sounds we use to indicate things or concepts are arbitrary and conventional. I don't have space in this post to go into the details of Magnus's findings, but I have repeated many of her experiments and I believe that phonemes are not entirely arbitrary.
The arapacana mantra, then, stands as an embodiment of a principle, put forward by the Mimamsa school on the basis of Upanishadic speculation, but taken up by Buddhists around the time of the rise of the Mahayana: that each and every articulate vocal sound has significance.
* see for instance: Richard Salomon. New Evidence for a Gandhari Origin of the Arapacana Syllabary. Journal of the American Oriental Society, Vol. 110, No. 2 (Apr - Jun, 1990), pp. 255-273
** Guy L. Beck. Sonic Theology. (Delhi : Motilal Banarsidass, 1995, 1993), pp.61.
Sound files from my evening on the Arapacana Alphabet at the Cambridge Buddhist Centre, 1 Nov 2007.
15/3/08. I've just added a page to visblemantra.org which pulls out the bits of the Pañcaviṃśatisāhasrikā Sūtra related to the Wisdom Alphabet meditation, with a few added comments.