eighteen Hinayana schools ［十八部・小乗十八部］ ( jūhachi-bu or shōjō-jūhachi-bu): Also, eighteen schools. Hinayana schools formed by schisms in the Buddhist Order after Shakyamuni’s death. According to The Doctrines of the Different Schools, a text of the Sarvāstivāda school, one hundred years after Shakyamuni’s death, the first schism occurred in the Buddhist Order and gave rise to the Sthaviravāda (Pali Theravāda) and Mahāsamghika schools. During the following hundred years, eight schools derived from the Mahāsamghika school. They were the Ekavyāvahārika, Lokottaravāda, Kaukkutika, Bahushrutīya, Prajnāptivādin (also, Prajnaptivādin), Chaityavādin, Aparashaila, and Uttarashaila schools.
The Sarvāstivāda school broke away from the Sthaviravāda school about two hundred years after Shakyamuni’s death and later gave rise to nine offshoots, totaling ten schools. The nine offshoots were the Vātsīputrīya, Mahīshāsaka, Kāshyapīya, Sautrāntika, Dharmottara, Bhadrayānīya, Sammatīya, Shannāgarika, and Dharmagupta schools. The eight schools that derived from the Mahāsamghika school, plus the ten schools that derived from the Sthaviravāda, or the Sarvāstivāda and its nine offshoots, together constitute the eighteen schools. If the original two schools, Sthaviravāda and Mahāsamghika, are added to the eighteen schools, then they form twenty Hinayana schools. The successive schisms that gave rise to these schools are said to have ceased by the beginning of the first century b.c.e.