The Six Roots, Six Dusts, and Six Consciousnesses

The Eighteen Realms include the six sense faculties, six sense objects, and six consciousnesses. The six sense faculties consist of the eye, ear, nose, tongue, body, and mind faculties. The first five sense faculties are composed of the four great elements (earth, water, fire, and wind). The superficial sense faculties (浮尘根) are located on the surface of the body, visible, tangible, and perceptible to the ordinary eyes of sentient beings. They can be destroyed and altered, exhibiting birth and cessation phenomena observable to the physical eye. The ultimate sense faculties (胜义根) of the five sense faculties are situated in the posterior region of the brain and can be seen through surgery; they are also material dharmas (色法) that are visible, tangible, and perceptible, subject to destruction and alteration, being impermanent dharmas of suffering characterized by birth and cessation. When the five sense faculties are damaged, the functions of the physical body become obstructed and cease, resulting in a vegetative state or even death.

In contrast, the mental faculty (意根) is not composed of the four great elements (earth, water, fire, and wind). It is formed from consciousness seeds; therefore, it is not a material dharma (色法) but a mental dharma (心法), possessing the functions and activities of consciousness. Material dharmas are conditioned dharmas (因缘所生法) without autonomy; they are passively born and manifested through the combined function of the Tathagatagarbha (如来藏) and the mental faculty, relying on the propelling force of the mental faculty. If the mental faculty does not propel, material dharmas immediately vanish. The mental faculty was not born later; it has coexisted with the Tathagatagarbha since beginningless kalpas, sustained continuously by the consciousness seeds provided by the Tathagarbha, requiring no other conditions. It is not a conditioned dharma. As long as the mental faculty has objects to grasp, it will not perish but continue to exist, and the world of the five aggregates (五蕴) will consequently undergo continuous birth and cessation. Although the five aggregates and five sense faculties ceaselessly arise and cease, the mental faculty never perishes. No one can annihilate the mental faculty, except when Arhats and Pratyekabuddhas enter Nirvana.

The functions of the mental faculty, which is an immaterial consciousness, differ vastly from those of the five material sense faculties. The five sense faculties lack the function of discernment, lack mental factors (心所法), and lack defilement or purity. They can be influenced by the mental faculty; their function of receiving the five sense objects (五尘) is directed by the mental faculty, yet they cannot direct the five sense objects or the five consciousnesses, much less direct the mental faculty. However, they can influence the mental faculty's feelings and decision-making.

The functions and activities of the mental faculty, as a mental dharma, are extremely potent. It possesses autonomy and decision-making authority over the body of the five aggregates, governing the birth, alteration, and even cessation of all worldly dharmas. It has the function of mental factors associated with consciousness, exhibiting both defilement and purity. It possesses the characteristics of discernment, discrimination, judgment, autonomy, seeking benefit and avoiding harm, selfhood and selflessness, ignorance and wisdom, habits and vexations, and the nature of conceptual proliferation (遍计所执性). It determines the cycle of birth and death for sentient beings, determines their progression toward Nirvana, the attainment of Buddhahood, and governs everything from the heavens to the earth. The five material sense faculties lack these characteristics; only the mental faculty, as a mental dharma, possesses them. Therefore, the mental faculty is a mental dharma, not a material dharma; it is an immaterial sense faculty, not a material one.

The term "faculty" (根) implies the function of giving rise to consciousness. However, this so-called "giving rise" is not direct production but rather the ability to cause the six consciousnesses to arise. It is the most direct condition for the birth of the six consciousnesses. The direct producer of the six consciousnesses is the Tathagatagarbha. The Tathagatagarbha utilizes karmic conditions and the six sense faculties to give rise to the six consciousnesses, but if the mental faculty is unattached to any dharma, the Tathagatagarbha cannot give rise to the six consciousnesses. Therefore, the condition provided by the five sense faculties for birth is very passive, while the condition provided by the mental faculty is extremely active and proactive. Its power to give rise to the six consciousnesses and all dharmas is immensely strong, and it also determines whether the five sense faculties are born or not. Such powerful autonomous driving force can only exist in an immaterial mental dharma; the material five sense faculties cannot possess it. Hence, the mental faculty is a mental dharma, not a material dharma; it is an immaterial sense faculty, not a material one.