Why Can't the Buddha Find the Eighth Consciousness in Nirvāṇa Without Remainder?

In nirvāṇa without remainder (Anupadhiśeṣa-nirvāṇa), there is no longer a body of the five aggregates (pañca-skandha), so the eighth consciousness has nothing to rely upon and cannot manifest its own mode of activity. Without a mode of activity in operation, none of the Buddha's consciousnesses can discover the eighth consciousness.

Finding the eighth consciousness and observing the eighth consciousness can only be done on the body of the five aggregates; observing the eighth consciousness must be done through its operations on the body of the five aggregates. Without a body of the five aggregates, the eighth consciousness cannot be observed. It is like observing the wind: one must observe the wind on trees or on objects. Without trees or objects, even if there is wind in empty space, it cannot manifest itself. The situation of the eighth consciousness should be the same as that of the wind.

Something formless and without marks can only manifest itself through dharmas that have form and marks; otherwise, being formless and without marks, how could it be discovered? For example, when you discover the wind, you must discover the coolness and refreshing quality of the wind blowing on your own body, or you must see clothes fluttering, trees swaying, or objects moving before you can discover the wind. If you did not have your own body of the five aggregates, how would you discover the wind? Without the swaying of external trees and grass, how would you discover the wind? To discover the wind, you must find it through these material forms, through the wind's mode of activity and its dynamic nature; you find the wind through the fluttering of objects, and you discover the wind through the refreshing, cool, cold, or warm sensations you feel when the wind blows on your body.

The same principle applies to finding the eighth consciousness: it must be perceived through the operations of the body of the five aggregates, through the activities of the five aggregates. When there is activity of the five aggregates, it indicates that the eighth consciousness is upholding, sustaining, and operating within the material body. Without a body of the five aggregates, the eighth consciousness cannot manifest.

The Buddha said in the Twelve Links of Dependent Origination Sūtra: name-and-form, the two of them, depend on each other; name-and-form conditions consciousness, and consciousness conditions name-and-form. Name-and-form refers to the five aggregates, and consciousness refers to the eighth consciousness, the Ālayavijñāna. The five aggregates can only operate by conditioning upon the eighth consciousness; without the eighth consciousness, there would be no five aggregates. "Consciousness conditions name-and-form" means that the Ālayavijñāna must condition upon the body of the five aggregates in order to manifest its own existence and operation; without a body of the five aggregates, the eighth consciousness cannot operate.