The ‘Third Council’ at Pāṭaliputra c.350 bce is not an historical fact so much as a scholarly hypothesis developed to explain the ‘Great Schism’ between the ‘Elders’ (Sthaviras) and the ‘Great Assembly’ (Mahāsaṃghikas), which was to have a profound effect upon the later tradition. This council is not mentioned in any canonical sources, and is not recognised by the Theravāda.who identify the Third Council with a later council at the same place held in the reign of Aśoka (see Council of Pāṭaliputra II). The circumstances surrounding the ‘Third Council’ are somewhat unclear, and there are two alternative explanations for why it was called. One concerns five theses put forward by a monk named Mahādeva to the effect that the Buddha was greatly superior in wisdom and compassion to the Arhat. The Mahāsaṃghikas accepted these five points and emphasized the Buddha's compassion and supernatural qualities, while the Sthaviras rejected them and held to the notion of the Buddha's nature as essentially human. The two groups were unable to reach agreement and went their separate ways. This explanation, however, which comes from sources over 400 years after the event, is almost certainly incorrect. Recent research shows that the ‘five theses’ have nothing to do with the early Mahāsaṃghikas and therefore can have nothing to do with with the initial schism with the ancestors of the Theriya tradition.
A second explanation for the split is that the division was caused by an attempt by the Sthaviras to introduce additional rules into the Vinaya which the Mahāsaṃghikas refused to accept. Most probably the schism was the product of a number of disagreements concerning both doctrine and monastic practice.