What kind of eye can see the characteristics of the tathāgatagarbha?

The tathāgatagarbha is formless and without characteristics, invisible to the physical eye, yet it can be seen by the mind eye, the wisdom eye, the dharma eye, and the buddha eye. Among these, the wisdom eye, the dharma eye, and the buddha eye are collectively called the mind eye; because of differences in wisdom, what these three eyes see differs greatly. How can the formless, characteristicless essence of the tathāgatagarbha be seen? Although the essence of the tathāgatagarbha is invisible, it has a great many modes of operation and functional activities. The modes of operation of the tathāgatagarbha are also called mental activities (citta-caitta) and mental factors; its functional activities are the accomplishment of the myriad dharmas and the tens of millions of dharmas, manifesting the appearances of all dharmas and endowing all dharmas with their corresponding functions. The wisdom eye, being shallower in wisdom than the dharma eye and the buddha eye and subject to obstructions, sees the modes of operation of the tathāgatagarbha only superficially and roughly; the dharma eye sees the modes of operation of the tathāgatagarbha extensively and in fine detail; the buddha eye is perfect and unobstructed, seeing the complete modes of operation of the tathāgatagarbha in their entirety—so subtle that there is not a single dharma it does not know, not a single dharma it does not understand, illuminating all of heaven and earth and perceiving the finest minutiae.

The modes of operation of the tathāgatagarbha can be observed through direct perception (pratyakṣa); those who have not attained enlightenment cannot observe them and can only speculate about the functions the tathāgatagarbha performs, unable to directly observe its modes of operation and functions. From this point alone, one can completely determine whether a person has awakened or not, and whether the awakening is genuine or false. The functional activities of the tathāgatagarbha can be learned about and imagined from the Buddhist sutras and from the teachings of the patriarchs and great masters; through inference one can also deduce their general functions, but it is very difficult to deduce them in any finer detail. Fine details, if they cannot be obtained through hearing, must be gained through one's own direct observation. Therefore, every practitioner who wishes to attain true great wisdom, with the wisdom eye and the dharma eye, must diligently cultivate precepts, meditation (samādhi), and wisdom, put in painstaking effort, and engage in genuine practice and realization; only then can there be the merit and benefit of true liberation.