Early Buddhist 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.
The textual sources agree that the first split was between the Sthaviravāda and the Mahāsāṃghika. However, after this initial division, more were to follow. Some modern scholars argue that the first split occurred in the intervening period between the second and third councils, and was probably about monastic discipline. However, only two ancient sources (the Dīpavaṃsa and Bhavya's third list) place the first schism before Aśoka, and none attribute the schism to a dispute on Vinaya practice.
Tradition largely holds that Buddhism split into 18 schools, but different sources give different lists of them, and scholars conclude that the number is merely conventional.
During and after the third council, elements of the Sthavira group called themselves Vibhajjavādins. One part of this group was transmitted to Sri Lanka and to certain areas of southern India, such as Vanavasi in the south-west and the Kañci region in the south-east. This group later ceased to refer to themselves specifically as "Vibhajjavādins", but reverted to calling themselves "Theriyas", after the earlier Theras (Sthaviras). Still later, at some point prior to the Dipavamsa (4th century), the Pali name Theravāda was adopted and has remained in use ever since for this group.
In addition, the Dipavamsa lists the following six schools without identifying the schools from which they arose: