Mahāyāna Buddhism is based principally upon the path of a bodhisattva. According to Jan Nattier, the term Mahāyāna ("Great Vehicle") was originally even an honorary synonym for Bodhisattvayāna, or the "Bodhisattva Vehicle." The Aṣṭasāhasrikā Prajñāpāramitā Sūtra contains a simple and brief definition for the term bodhisattva, which is also the earliest known Mahāyāna definition. This definition is given as the following.
Mahāyāna Buddhism encourages everyone to become bodhisattvas and to take the bodhisattva vows. With these vows, one makes the promise to work for the complete enlightenment of all sentient beings by practicing the six perfections. Indelibly entwined with the bodhisattva vow is merit transference (pariṇāmanā).
In Mahāyāna Buddhism life in this world is compared to people living in a house that is on fire. People take this world as reality pursuing worldly projects and pleasures without realizing that the house is on fire and will soon burn down (due to the inevitability of death). A bodhisattva is one who has a determination to free sentient beings from samsara and its cycle of death, rebirth and suffering. This type of mind is known as the mind of awakening (bodhicitta). Bodhisattvas take bodhisattva vows in order to progress on the spiritual path towards buddhahood.
There are a variety of different conceptions of the nature of a bodhisattva in Mahāyāna. According to some Mahāyāna sources a bodhisattva is someone on the path to full Buddhahood. Others speak of bodhisattvas renouncing Buddhahood. According to the Kun-bzang bla-ma'i zhal-lung, a bodhisattva can choose any of three paths to help sentient beings in the process of achieving buddhahood. They are:
- king-like bodhisattva - one who aspires to become buddha as soon as possible and then help sentient beings in full fledge;
- boatman-like bodhisattva - one who aspires to achieve buddhahood along with other sentient beings and
- shepherd-like bodhisattva - one who aspires to delay buddhahood until all other sentient beings achieve buddhahood. Bodhisattvas like Avalokiteśvara and Śāntideva are believed to fall in this category.
According to the doctrine of some Tibetan schools (like Theravāda but for different reasons), only the first of these is recognized. It is held that Buddhas remain in the world, able to help others, so there is no point in delay. Geshe Kelsang Gyatso notes:
- In reality, the second two types of bodhicitta are wishes that are impossible to fulfill because it is only possible to lead others to enlightenment once we have attained enlightenment ourself. Therefore, only king-like bodhicitta is actual bodhicitta. Je Tsongkhapa says that although the other Bodhisattvas wish for that which is impossible, their attitude is sublime and unmistaken.
The Nyingma school, however, holds that the lowest level is the way of the king, who primarily seeks his own benefit but who recognizes that his benefit depends crucially on that of his kingdom and his subjects. The middle level is the path of the boatman, who ferries his passengers across the river and simultaneously, of course, ferries himself as well. The highest level is that of the shepherd, who makes sure that all his sheep arrive safely ahead of him and places their welfare above his own.