What Is the Inner and Outer Mind-Consciousness?

When the Buddha expounded on the five hindrances in the Mahasatipatthana Sutta, he spoke of internal sensual desire and external sensual desire, internal ill will and external ill will, internal sloth-and-torpor and external sloth-and-torpor, internal restlessness-and-worry and external restlessness-and-worry, internal doubt and external doubt. What do the internal and external refer to respectively?

If the mind is divided into internal and external, the external mind refers to the mind-consciousness that sentient beings can commonly perceive and observe, while the internal mind refers to the mind-root that sentient beings find difficult to perceive and observe. These two types of consciousness are: one manifest, one hidden; one apparent, one obscure; one shallow, one deep; one easily changeable, one firmly entrenched and difficult to alter. Spiritual practice first addresses the superficial level of consciousness, then penetrates to the deep level of the mind-root. It initially transforms the consciousness provisionally and ultimately transforms the mind-root completely. Therefore, all afflictions and ignorance are initially and most evident at the level of consciousness, but ultimately and most profoundly rooted at the level of the mind-root.

From this sutra, we can see that although the Buddha did not explicitly teach the Dharma concerning the mind-root when expounding the Hinayana teachings, he nevertheless implicitly addressed it. He implied that all afflictions and ignorance pertain to the mind-root, that eradicating afflictions means eradicating the afflictions of the mind-root, that liberation is the liberation of the mind-root, and that all phenomena ultimately pertain to the mind-root. By resolving the problem of the mind-root, one resolves all phenomena, ultimately attaining Nirvana and liberation.