Early Buddhist schools

The early Buddhist community initially split into two main Nikāyas (monastic groups, divisions): the Sthavira ("Elders"), and the Mahāsāṃghika ("Great Community"). This initial split occurred either during the reign of Aśoka (c. 268-232 BCE) or shortly after (historians disagree on the matter).

Later, these groups became further divided on doctrinal grounds into numerous schools of thought and practice (each with their own monastic rules and doctrinal Abhidharma texts). Some of the main sects included the Sarvāstivādins ("Temporal Eternalists"), the Dharmaguptakas ("Preservers of Dharma"), Lokottaravādins ("Transcendentalists"), the Prajñaptivādins ("Conceptualists"), the Vibhajyavādins ("Analysts"), and the Pudgalavādins ("Personalists"). According to traditional accounts these sects eventually proliferated into 18 (or, less-commonly, 20) different schools.

The textual material shared by the early schools is often termed the early Buddhist texts and these are an important source for understanding their doctrinal similarities and differences. There were various works of Abhidharma and other treatises written by these schools that contain more unique doctrines specific to each school.

Formation and development

The First Council

According to the scriptures (Cullavagga XI.1 ff), three months after the parinirvāṇa of Gautama Buddha, some of the arahants among his disciples held a council—presided over by Mahākāśyapa, one of the most senior disciples—at Rajagaha (Rajgir), with the support of king Ajātasattu, and there recited the teachings of the Buddha. The scriptures of the various schools differ, in their accounts of the council, as to what was actually recited there. An elder monk named Purāṇa is recorded as having said: "Your reverences, well-chanted by the elders are the Dhamma and Vinaya, but in that way that I heard it in the Lord's presence, that I received it in his presence, in that same way will I bear it in mind."; this is taken by Paul Williams to suggest some disagreement about the accuracy of the canon even at that time. According to Theravāda tradition, the teachings were divided into various parts and each was assigned to an elder and his pupils to commit to memory, and there was no conflict about what the Buddha taught.

Some scholars argue that the First Council did not actually take place.

Divergence between the Sthavira and the Mahāsāṃghika

The expansion of orally transmitted texts in early Buddhism, and the growing distances between Buddhist communities, fostered specialisation and sectarian identification. One or several disputes did occur during Aśoka's reign, involving both doctrinal and disciplinary (Vinaya) matters, although these may have been too informal to be called a "council". The Sthavira school had, by the time of Aśoka, divided into three sub-schools, doctrinally speaking, but these did not become separate monastic orders until later.

In Theravādin tradition, the first schism's precipitating dispute is supposed to have occurred during the Second Council at Vaishali, approximately one hundred years after Gautama Buddha's parinirvāṇa; the result of the council was—according to this tradition—the first schism in the Saṅgha, between the Sthavira and the Mahāsāṃghika, though the exact cause of the split is not well agreed-upon. While the Second Council probably was an historical event, details regarding its course and outcome are less certain.

Lamotte and Hirakawa both maintain that the first schism in the Buddhist Saṅgha occurred during the reign of Aśoka; Collett Cox places the date slightly later, writing that "most scholars would agree that even though the roots of the earliest recognised groups predate Aśoka, their actual separation did not occur until after his death." Only two ancient sources (the Dīpavaṃsa and Bhāviveka's third list) place the first schism before Aśoka, and only one (the Mahāsāṃghika Śāriputraparipṛcchā) attributes it to a dispute on Vinaya; several (especially Sthaviravādin) sources give the cause as a dispute over doctrine.

The various splits within the monastic organizations went together with the introduction and emphasis on Abhidharmic literature by some schools. This literature was specific to each school, and arguments and disputes between the schools were often based upon these Abhidharmic writings. However, modern scholars generally hold the first schisms to have been based upon disagreements on Vinaya (monastic discipline), though it is also asserted that—by c. 100 CE or earlier—they could be based upon doctrinal disagreement. Pre-sectarian Buddhism, however, did not have Abhidharmic scriptures, except perhaps for a basic framework, and not all of the early schools developed an Abhidharma literature.

Third Council under Aśoka

Theravādin sources state that, in the 3rd century BCE, a council was convened under the patronage of Aśoka. Some scholars argue that there are certain implausible features of the Theravādin account which imply that the Third Council was ahistorical. The remainder consider it a purely Theravāda-Vibhajyavāda council.

According to the Theravādin account, this council was convened primarily for the purpose of establishing an official orthodoxy. At the council, small groups raised questions about the specifics of the Vinaya and the interpretation of doctrine. The chairman of the council, Moggaliputta Tissa, compiled a book, the Kathāvatthu, which was meant to refute these arguments. The council sided with Moggaliputta and his version of Buddhism as orthodox; it was then adopted by Emperor Aśoka as his empire's official religion. In Pali, this school of thought was termed Vibhajjavāda, literally "thesis of [those who make] a distinction".

The distinction involved was as to the existence of dharmas in the past, future, and present. The version of the scriptures that had been established at the Third Council—including the Vinaya, Sūtra, and Abhidharma Piṭakas (collectively known as the Tripiṭaka)—was taken to Sri Lanka by Emperor Aśoka's son, the monk Mahinda. There it was eventually committed to writing in the Pali language. The Pali Canon remains the most complete set of surviving Nikāya scriptures, although the greater part of the Sarvāstivādin canon also survives in Chinese translation (along with parts of other—sometimes unidentified—canons); some parts exist in Tibetan translations; and some fragments exist in Sanskrit manuscripts, and in some other Indo-Aryan languages (e.g., Gāndhārī).

Further divisions

Some time after the reign of Aśoka, further divisions began to occur within the Buddhist movement, and a number of additional schools emerged. Étienne Lamotte divided the mainstream Buddhist schools into three primary doctrinal types:

1. The "personalists", such as the Pudgalavādin Vātsīputrīyas and Saṃmittīyas.
2. The "realists"; namely, the Theravāda and Sarvāstivāda Ābhidharmikas.
3. The "nominalists"; e.g., the Mahāsāṃghika Prajñaptivādins, and possibly non-Abhidharma Sthaviravādins.

One Sthavira faction—based (in part) in Sri Lanka, and in certain areas of South India (such as Vanavasi in the southwest and the Kañci region in the southeast)—began to call themselves the Vibhajyavādins; this group later ceased to refer to themselves specifically as "Vibhajjavādins", but reverted to calling themselves "Theriyas", after the earlier Theras (Sthaviryas). Still later, at some point prior to the Dīpavaṃsa (4th century), the Pali name Theravāda was adopted and has remained in use ever since for this group.

Other groups included the Sarvāstivāda, the Dharmaguptakas, the Saṃmitīya, and the Pudgalavādins. The Pudgalavādins were also known as Vātsīputrīyas, after their putative founder. Later, this group became known as the Saṃmitīya school, after one of its subdivisions. It died out around the 9th or 10th century. Nevertheless, during most of the early medieval period, the Saṃmitīya school was numerically the largest Buddhist group in India, with more followers than all the other schools combined. The Sarvāstivādin school was most prominent in the Northwest India, and provided some of the doctrines that would later be adopted by the Mahāyāna. A related group was the Sautrāntika school, which only recognised the authority of the sūtras, and which rejected the Abhidharma transmitted and taught by the Vaibhāṣika wing of the Sarvāstivāda. Based on textual considerations, it has been suggested that the Sautrāntikas were actually adherents of Mūlasarvāstivāda. The relation between the Sarvāstivāda and the Mūlasarvāstivāda, however, is unclear.

All of these early schools of Nikāya Buddhism eventually came to be known collectively as "the eighteen schools" in later sources. With the exception of the Theravāda—and, in Tibet alone, the Mūlasarvāstivāda—none of these early schools survived beyond the late medieval period (by which time, several were long-extinct already); however, a considerable amount of the canonical literature of some of these schools has survived, mainly in Chinese translation. Moreover, the origins of specifically Mahāyāna doctrines may be discerned in the teachings of some of these early schools; in particular, those of the Mahāsāṃghika and the Sarvāstivāda.

The schools sometimes split over differences concerning the "real" meaning of teachings in the Sūtra Piṭaka, and sometimes over disagreement concerning the proper observance of Vinaya. These differences became embedded in large works such as the Abhidharmas and commentaries. Comparison of existing versions of the Sūtra Piṭakas of various sects shows evidence that doctrines from the Abhidharmas sometimes found their way back into the Sūtra Piṭakas to support the statements made in those Abhidharmas.

Some of these developments may be seen as later elaborations on the teachings. According to Gombrich, unintentional literalism was a major force for change in the early doctrinal history of Buddhism; i.e., texts were interpreted according to a strict literal reading of the words used therein, with little consideration paid to other hermeneutic techniques.