The mind-base and mental factors are the guiding principle of practice and also the operating system of practice.

“Direction” means that the mental factors (caitasika) can direct one toward the goal of one’s own practice, eradicate ignorance, subdue and eliminate afflictions, transform mental activities, and transform karmic seeds. “Return” means to let the mind return to wisdom, to purity, and to liberation. The operating system, in accordance with the mental factors, continuously corrects and transforms the mental factors. Actual practice is the process of operating the mental factors and the operational process of the mental factors; it is the process of the mind transforming itself.

The reason why mental factors can change is due to the successful permeation of the mental consciousness (manovijñāna) upon the mental faculty (manas). The mental faculty abandons evil and moves toward good, thereby transforming its own mental activities. The fundamental cause of this transformation is the Tathāgatagarbha (Thus-Come One’s Womb/Storehouse). It is the Tathāgatagarbha that transforms the mental factors of the mental faculty. However, the Tathāgatarbha is not the dominant consciousness; it does not take the initiative and lacks subjective initiative. It passively transforms seeds in accordance with the mental activities of the mental faculty. When seeds are transformed, the results are also transformed. Although the arising of all phenomena is produced by the Tathāgatagarbha, the driving force behind it is the mental factors of the mental faculty. If the mental faculty does not intend to act, the Tathāgatagarbha remains inactive, and no phenomena arise.

The mental faculty possesses subjective initiative. When its nature is transformed, it prompts changes in karmic seeds. The transformation of mental factors is the cause, and the change of karmic seeds is the result. The mental faculty’s recognition of truth and its direct realization of truth are the cause, and the transformation of mental factors is the result. The mental faculty’s diligent cultivation of the thirty-seven factors of enlightenment (bodhipākṣika dharmas) is the cause, and direct realization is the result. The mental consciousness’s proper permeation and guidance are the cause, and the mental faculty’s being permeated is the result. Of course, in actual practice, every step causes the mental factors of the mental faculty to change. The change of mental factors is the result, while the cause remains the mental faculty’s own mental factors prompting corresponding changes in itself. The prerequisite is that the mental factors of the mental consciousness must propel the mental factors of the mental faculty.

Mental factors necessarily arise simultaneously with the consciousness.

Mental factors are the companions of the consciousness. They must accompany the operation of the consciousness; otherwise, the consciousness would be inactive. Whenever a consciousness arises, mental factors necessarily arise simultaneously. Without mental factors, the consciousness cannot function, and thus all phenomena in the world could not arise or exist. Even the operation of the eighth consciousness requires the coordination of its own mental factors. The very existence of the eighth consciousness itself is inseparable from the accompaniment of mental factors.

The arising and operation of the four kinds of sustenance (āhāra) are all functions of the consciousness. Since the consciousness is inseparable from the accompaniment of mental factors, the four kinds of sustenance are likewise inseparable from mental factors. Ordinary beings cannot be free from the four kinds of sustenance, and even noble beings (ārya) in the desire realm of the human world cannot be free from them. Beings with relatively high meditative attainments can be free from solid food (kavaḍīkārāhāra) and mental volitional food (manasañcetanāhāra), and sometimes can also be free from contact food (sparśāhāra), but they cannot be free from consciousness food (vijñānāhāra). The most fundamental needs of a sentient being’s life require the consciousness food of the eighth consciousness and the seventh consciousness.