The functioning of the eighth consciousness is extremely subtle and difficult to comprehend. Fearing that those attached to a mistaken view of self would wrongly grasp it as a self, the Buddha deliberately did not teach it explicitly in the Agama sutras. However, practitioners of the two vehicles misunderstood
The vast scripture store is inexhaustible, Deep as the ocean, stirred by seven waves of sense, The outer world becomes the wind. It receives impressions, holds seeds, through sense organs and the world, Coming last, going first, it acts as master.
This eighth consciousness has the qualities of being able to store, being stored, and being clung to. That is why it is vast beyond measure, with no edge to be found, and deep beyond reach, with no bottom or source to be grasped. This consciousness holds the seeds of all the changing consciousnesses, so it is called "that which can store." It receives the seeds produced by the changing consciousnesses through their influence, so it is called "that which is stored." It is grasped as a self by the seventh consciousness, so it is called "that which is clung to."
This consciousness is like water. The first seven changing consciousnesses arise dependent on it, like waves. The objects and appearances that emerge from this consciousness act as a supporting condition for the changing consciousnesses, like a strong wind. This consciousness is neutral and undifferentiated, flowing continuously without interruption, and so it receives the influence of the first seven changing consciousnesses. It holds the seeds of all phenomena, the inner sense faculties and body, and the outer material world. At the moment of death, this consciousness is the last to depart. At the moment of birth, this consciousness is the first to take hold. Although it is not an actual self or a real entity, throughout a single lifetime of birth and death, it functions as the fundamental link that ties
Before the Unmovable Ground, the Storehouse Consciousness is finally shed; After the Vajra Path, the Fruit of Recompense is emptied.
Great Perfect Mirror Wisdom and Undefiled Consciousness arise together, Illuminating all realms in the ten directions, within worlds as numerous as dust.
This consciousness has many names. One is Alaya Consciousness, because it is grasped as a self by the seventh consciousness. This name is abandoned when self-grasping is permanently subdued at the stage of the Ground of Immovability. Another name is Maturation Consciousness, because it is brought about by the ripening of wholesome and unwholesome actions, both tainted and untainted. This name is only shed upon reaching the perfect Buddha fruit after the Vajra Path. A third name is All-Seed Consciousness, which pervades both causes and results, as well as ordinary and noble states. But after becoming a Buddha, it only holds perfect, untainted wholesome seeds, benefiting beings throughout the future without ever being habituated again—because all tainted seeds and inferior untainted seeds are forever eradicated. It is then called the Immaculate Consciousness, because it constantly associates with the supremely good, untainted mental factor of wisdom, and is called the Great Perfect Mirror Wisdom. Once this consciousness is transformed and this wisdom arises, the entire realm of reality becomes clear and luminous, with equal insight into both ultimate and conventional truths. Therefore it is said to universally illuminate the countless realms throughout the ten directions.