Mahayana/Theravada III: The Great Schism.
The Buddha was very concerned with schism in the sangha. He defined schism very clearly, warned about its arising in no uncertain terms, and put many policies and procedure in place to avoid. The sangha here is understood as the community of monks and nuns, and the Buddha is reported to have averted a serious attempt at schism on the part of his cousin Devadatta, who had ambitions for leadership of the sangha.
Many accounts of the Mahayana trace its origins to a schism in the sangha reported to have occurred around 100 years after the death of the Buddha. The assumption is common that Theravada and Mahayana therefore have had irreconcilable differences ever since. I would like to show here that there probably never was an historic schism that separated Mahayana from Theravada or any of the other "Hinayana" schools, and to caution that assuming that there was might effectively induce one.
The great schism of about 350 BC reportedly resulted in a group of monks called the Mahasanghika walking out of the Second Buddhist Council and forming their own order, by some reports for reasons of doctrine and by others for reasons of discipline. Doctrine here means Dharma/Dhamma and discipline means Vinaya, principles of conduct for the monastic community. In fact, from the period 350 BC to 100 BC (I'm looking at a book here by Nalinaksha Dutt, Buddhist Sects in India), there seems to have been three principle factions of Buddhism, a forerunner of Theravada, the Sarvastivadins and the Mahasanghika, along with many minor ones. These three sects seemed to have doctrinal differences, but also influenced each other. For instance, the Theravadins and the Sarvastivadins composed competing Abhidharmas during this period. Dutt reports that the idea of the Bodhisattva first arose in the Sarvastivadin school during this period, as something that had particular appeal lay practitioners, then spread to the other two schools. Apparently most of the Jataka stories found in the Pali Canon were in fact composed by Sarvastivadin authors to illustrate the ideal of the Bodhisattva, then incorporated by the Theravadins into the Pali scriptures. The Mahasanghika advocated a higher status for the Buddha than that of a mere omniscient, psychically powerful human. However, Dutt considers all of these schools to be Hinayana.
Mahayana apparently developed centuries later in India and its exact connection to any of these schools is obscure. The bodhisattva ideal (Sarvastivadin) became a central feature of the Mahayana, but at the same time the equally important emphasis of the Mahayana on emptiness and the perils of conceptual thinking is considered by some scholars to have developed in direct opposition to the radical Sarvastivadin idea that gave the school its name, the idea that things in fact exist. The Mahayana produced, or later claimed for itself, a line of brilliant and creative thinkers, and a very rich mythology, populated by such figures as Avalokiteshvara (Guan Yin), Manjushri and Samantabhadra.
When considering doctrinal variation in Buddhism, we can ask, "Is it true?" or "Did the Buddha say (something like) that?" But before we do that, we might ask, "Does it matter?" I'm not convinced, for instance, that belief in a transcendental Buddha either brings one closer or brings one further away from liberation. However, the question here is, "Are the doctrinal differences between the Mahayana and non-Mahayana schools great enough to cause a schism?"
Apparently not: Chinese pilgrims traveled to India in the Fourth to Sixth Centuries AD. These were Mahayana monks who knew that they might encounter "Hinayana" Buddhists in their travels. To their great surprise they found Mahayana monks living in the same monasteries, eating the same food, with Theravada monks, sacrificing no harmony over doctrinal matters. They lived like modern roommates one of whom reads mysteries and one of whom reads science fiction. It is not something one fights over.
The pilgrims returned to China, Buddhism eventually died out in India, Theravada Buddhism came to dominate the South of Asia, Mahayana thrived in the North, and for many centuries there was little opportunity for contact. However, this geographical dispersal of the schools of Buddhism was never, as far as I can see, the result of a schism in the sangha. It is more like a family separated for many generations through immigration, now divided even by language, but now reunited. Or maybe like a family reunited, but now with a lingering rumor of an ancient family feud. What will its future be?
We have not one, but two strong traditions each of which preserves essence of the Buddha's tradition (sometimes in its own way). That's great: we have someone we can swap leisure-time reading with.