[page 70] Sacred texts or scriptures, transmitted either orally or in written form, are common to all the world's religious traditions. In some traditions these texts are relatively brief and unitary, like the Koran, for example. In others they are longer and spring from various sources, but are brought together in a single compilation, as in the case of the Christian Bible. In such instances the resulting collection is known as a canon, which is not one book, but many. These many books, however, share a common identity by virtue of the particular sanctity or authority attributed to them, which sets them apart from other books. Not every work of religious literature is scripture, after all, but only that which for some reason is thought to be especially sacred. For Buddhists, whose canonical literature is extraordinarily prolific, the sacredness of their scriptures depended originally on their utterance by the Buddha, Siddhārtha Gautama. Insofar as we can determine it, the canon1 transmitted by Gautama's followers after his death consisted of two principal sets of texts, the Dharma or Sūtras (discourses delivered by the Buddha, or in some cases by his disciples, but with his blessing) and the Vinaya (the corpus of monastic regulations, with the various traditions relating to their original promulgation).[page 71] Later most schools added a third collection of summaries and systematic restatements of doctrine, the Abhidharma. These three collections or "baskets" (piṭaka) were passed down orally for several centuries, and as the Buddhist community split into different ordination lineages and schools, the Buddhist canon or Tripiṭaka ("Three Baskets"), which can hardly have been fixed even in the lifetime of the founder, diverged correspondingly, so that by the beginning of the Common Era there were various "canons" in existence. (Of these only one has survived to the twentieth century relatively complete, but with later modifications that scholars are now beginning to address: the Pāli Canon of the Theravādin school, which was committed to writing in the first century B.C.E.) We are unsure precisely to what extent these collections were ever considered "closed," setting the texts in them apart from others in circulation, but we know that Buddhists worked with very definite ideas about authenticity, about what could be accepted as the word of the Buddha (buddhavacana) and what could not (see Lamotte; Ray; Davidson). And we also know that Buddhists of all "Mainstream" schools (on this term see Harrison, 1992b: 45, n. 8) continued to produce works of literature, which caused no problems as far as the borderline between the canonical and the non-canonical was concerned, as long as they were not attributed to the Buddha.

This situation changed around the beginning of the Common Era with the advent of the Mahāyāna, a loose pan-Buddhist movement which, while it may have found more favorable conditions for growth within some Mainstream schools than others, soon overran their sectarian boundaries. To promote the various doctrinal and cultic innovations which were their characteristic concern, the followers of the Mahāyāna produced an enormous number of new texts claiming the status of buddhavacana. These then circulated in an uneasy relationship with the canons of the traditional schools, which had in many cases furnished the raw materials for their composition. Although this was in one sense an "anti-canon," co-existing with the Mainstream collections in India while challenging their claims to exclusive authenticity and completeness, this alternative set of scriptures was itself never "closed." Rather, it remained an "open canon," a contradiction in terms evidently occasioned by the need to assign the texts a certain primacy and yet not close the door on further creativity.2 As for the contents of this "canon," we can only speculate as to what[page 72] texts were available at any given time or place,3 but we may assume that most Mahāyānists can hardly have had at their disposal the huge collections of their scriptures we now possess. It is much more likely that, in addition to the traditional canons of the schools they belonged to, they had access to a limited number of Mahāyāna texts, in some cases perhaps to compendia of them. We know of two of these major sūtra collections, the Mahāsaṃnipāta and the Ratnakūṭa, the compilation of which poses difficult historical problems, although some of the texts in them are known to date back to the beginnings of the Mahāyāna. Alongside them we might also place "mega-scriptures" like the Avataṃsaka and the various longer versions of the Prajñāpāramitā ("Perfection of Wisdom"), one of the most philosophically important productions of the Mahāyāna. Such longer texts and text-compendia may well have done duty as a type of Mahāyāna Buddhist canon.

This situation was further complicated when a new movement known as the Vajrayāna or Tantric Buddhism began to take shape towards the middle of the first millennium. In fact the production of sacred literature simply continued unabated, while the themes addressed changed to suit the needs and tastes of the times. In this new wave of works, which are known as tantras, the ritual and iconographical repertoire of Mahāyāna Buddhism was extended, while its doctrines were stretched and remolded so as to harness the power of sexual desire and the potency of sexual symbolism (among other things) in the service of the quest for liberation. Although the tantras do indeed qualify as scriptures, given the circumstances of their production and use, a tantric canon was even less likely to emerge than a Mahāyāna canon. By the close of the first millennium, then, towards the end of its life in its homeland, Indian Buddhism was a complex amalgam of three strains—Mainstream, Mahāyāna and Vajrayāna—and it is this multi-layered tradition and its equally complex scriptural heritage which the Tibetans have inherited and passed down to the present day. Without some appreciation of this background, it is impossible to understand the canon which the Tibetans developed.