Why Can Manas and Vijñāna Communicate with Each Other?

For example, when the manas (mental faculty) desires to eat, the tathāgatagarbha (Buddha-nature) complies with the intention of manas, giving rise to mano-vijñāna (mind consciousness). Manas then conveys to mano-vijñāna the task of discerning the various dishes before it, selecting among them the preferred food to eat. Mano-vijñāna can comprehend the thoughts of manas, and after mano-vijñāna performs its discernment, manas can also comprehend the thoughts of mano-vijñāna; the two can communicate with each other instantaneously. However, when manas discerns phenomena from past lives and conveys them to mano-vijñāna, mano-vijñāna is unable to comprehend them or can only understand a little. Why is this? It is because mano-vijñāna has not experienced past lives and thus has no memory of them, rendering it incapable of discernment.

Manas decides to discern the various dishes to determine which one to eat, and mano-vijñāna arises to perform this discernment on behalf of manas. After mano-vijñāna discerns and judges the characteristics of each dish, it conveys this information to manas. Upon understanding, manas then decides what to eat. It is also possible that mano-vijñāna, relying solely on observation together with eye consciousness, cannot discern comprehensively. Therefore, manas decides to taste a little, causing tongue consciousness and nose consciousness to participate together in the discernment and judgment. After manas receives and understands the information, it knows which dish is delicious and to its liking, and thus begins eating heartily, ignoring the unpalatable ones.

These dishes can be directly contacted (experienced) by mano-vijñāna together with the five sense consciousnesses (eye, ear, nose, tongue, body), hence there is sensation (vedanā), perception (saṃjñā), and mental formation (cetanā), enabling judgment. Regarding phenomena from past lives, without supernatural powers (abhijñā), the five sense consciousnesses cannot contact them at all. Mano-vijñāna lacks the power of mind-reading (cetopariyañāṇa), has no experience, and possesses insufficient wisdom (prajñā), thus it cannot know the thoughts and contemplations within manas. If mano-vijñāna possesses great wisdom, it can clearly discern the dharmas (phenomena, mental objects) contemplated or implied within manas.

Why can mano-vijñāna and manas convey intentions to each other? It is because manas contacts mental objects (dharmas), giving rise to mano-vijñāna. The three (manas, dharmas, and mano-vijñāna) then come together in contact. Regarding mental objects (dharmas), not only can manas discern them, but mano-vijñāna can also discern them, differing only in the degree and clarity of discernment. During this process, mano-vijñāna and manas are also constantly in contact with each other; mind contacts mind. Naturally, they can mutually know each other's intentions, with the difference lying in the degree of knowing, involving depth and scope. As long as mano-vijñāna exists, it is necessarily in contact with manas. Therefore, their respective intentions can be transmitted and communicated at any time and place. If the communication is poor, psychological dissonance arises; if the communication is smooth, the mood becomes pleasant. This bears some resemblance to the relationship between two individuals interacting.