The Difference and Boundary Between the Six Internal Sense Bases and the Six External Sense Bases

The objects perceived by our six consciousnesses are all within the inner six realms; the outer six realms cannot be directly perceived. The outer six realms are constituted by the actual four great elements and the seeds of the five great elements; they are substantial material forms (rūpa-dharma), representing the essential realm. This part of material form corresponds exclusively to the Tathāgatagarbha. In contrast, the inner six realms are the objective realm with substance (sad-artha); they are not the most substantial material forms but are realm-based material forms imbued with the substantial essence of the outer six realms' five great element seeds. They are no longer the original substantial material forms, much like an image in a mirror—though similar in shape, it cannot be touched. What can be touched is the substantial material form; what is empty and cannot be touched is the similar, illusory dharma, and thus it has no practical utility.

Since what the six consciousnesses perceive is illusory dharma, devoid of practical utility, why do sentient beings use it every day? In truth, sentient beings do not engage in real utilization either. What is called "use" is merely sensation. Sensation is illusory, and what is sensed is also illusory. This is a difficult gap to cross; only after realizing emptiness through direct experience can one see through it.

So, where is the boundary between the inner six realms and the outer six realms? After the Tathāgatagarbha initially transforms and generates the six realms using the seeds of the five great elements, the mental faculty (manas) perceives dharmas based on the Tathāgatagarbha. However, what the mental faculty perceives differs from what the Tathāgatagarbha perceives. The appearances seen by the mental faculty are material forms bearing the characteristics of the conventional world, belonging to conventional dharmas. What the Tathāgatagarbha perceives is not conventional dharmas; it lacks conventional appearances. Sentient beings fundamentally cannot comprehend this part. After the mental faculty perceives the dharmas, the Tathāgatagarbha then transmits the dharmas onward to the superior sense bases (adhipati-pratyaya). During this transmission, the material forms are continuously arising, ceasing, and transforming until they reach the superior sense bases. What the six consciousnesses perceive by then is no longer the six realms outside the superior sense bases. The six realms begin to change as soon as the mental faculty perceives them; by the time the six consciousnesses perceive them after the mental faculty, they are no longer the original six realms.

Thus, the six realms can be broadly divided into three levels: first, what is perceived by the Tathāgatagarbha; second, what is perceived by the mental faculty; third, what is perceived by the six consciousnesses. The further along this sequence, the less substance the six realms carry, the greater the transformation, the more alterations occur, and the more illusory and unreal they become—much like images reflected through three layers of mirrors. When the isolated mental consciousness (manovijñāna) subsequently recalls, fantasizes, and compares these images within the mind, that realm possesses not even a trace of substance. After the six consciousnesses differentiate and discern these manifold images, the arising of thoughts and mental activities affects the mental faculty. The mental faculty, stirred again, influences the Tathāgatagarbha. If the karmic seeds permit, it will alter the essential realm—the outer six realms. When the outer six realms change, the subsequently arising inner six realms will also change, and the world transforms. But what would be the result if the six consciousnesses did not differentiate these layered images and remained unmoved by them?