two vehicles ［二乗］ ( nijō): The vehicles or teachings that lead voice-hearers ( shrāvaka) and cause-awakened ones (pratyekabuddha) to their respective levels of enlightenment. The vehicle of voice-hearers was intended to lead persons of that capacity to the state of arhat via the teaching of the four noble truths; the vehicle of cause-awakened ones leads those individuals to the awakening to the truths of impermanence and of causal relationship via the teaching of the twelve-linked chain of causation. In early Buddhism, pratyekabuddhas, or cause-awakened ones, referred to those who lived apart from human habitation; with no chance to hear the Buddha’s teachings, they nevertheless realized the impermanence of all things by observing changes in nature such as the scattering of blossoms or the falling of leaves. Hence they were also called self-awakened ones.
Buddhist texts describe two kinds of self-awakened ones: The first are those who were originally the Buddha’s voice-hearer disciples but who, on reaching the stage just below arhatship, chose to practice alone toward the goal of becoming arhats. The second are those who practiced alone in an age without a Buddha and without learning from anyone and achieved a level of enlightenment. Mahayana Buddhism describes the two vehicle teachings as “lesser vehicles,” or Hinayana teachings. The provisional Mahayana teachings condemn persons of the two vehicles for seeking their own enlightenment without working for the enlightenment of others, and assert that they can never attain Buddhahood. The Lotus Sutra reveals the one vehicle of Buddhahood and identifies all three vehicles—those of voice-hearers, cause-awakened ones, and bodhisattvas—as expedient means that lead people to the one Buddha vehicle. According to the Lotus Sutra, therefore, even those of the two vehicles can become Buddhas. This is substantiated in the sutra by Shakyamuni’s prophecy that all of his voice-hearer disciples will in the future become Buddhas, specifying when and where this will take place and what names they will assume at that time.