What is the separation of mind and matter, and the separation of mind from mind?

After contemplative practice (vipaśyanā-caryā) gains strength, first the mind and material form separate, and then mind separates from mind. The separation of mind and material form is easy to understand and observe, but what is the state of mind separating from mind, and how can it be observed?

He Qianxing: I myself do not know whether mind has separated from mind; I suppose it has not yet completely separated. I only feel that the mind of fear has faded a great deal. In the past I feared physical harm, feared the future, and feared that my body would not be cared for. Now I feel that the body is a wooden tool; touching my body is like touching an external object, and so there is no more fear. As for how to observe it: when the mind settles down, the arising of mental thoughts is observed very clearly—arising and then vanishing, the mind standing outside of thoughts, with thoughts drifting to and fro like dust. This disciple's level is still very low, so I do not even know how to describe it.

Assessment: Why was there fear in the past? Because there was worry. Why was there worry? Because of fearing loss and fearing not gaining—anxiety over gain and loss. Why the anxiety over gain and loss? Because the body and mind and the five aggregates (pañca-skandha) were taken as one's own, grasping at the gains and losses of the five aggregates of body and mind; unable to let go of oneself inwardly, one becomes anxious over gain and loss, with worry and fear in the mind. When cultivation reaches the point of seeing the body and mind as empty and seeing the five aggregates as empty, there is no more fear.

The separation of mind and material form is the mind leaping outside the body to objectively observe the physical body, just like observing a piece of wood unrelated to oneself—without emotion, not taking the physical body as one's possession. At this point, the elimination of the view of the body (ātma-dṛṣṭi) is not far off. The separation of mind from mind is likewise the mind leaping outside of the mind itself, objectively and dispassionately observing the mind's various activities, various thoughts, various ideas, and various emotional fluctuations—wholesome, unwholesome, and neutral (avyākṛta) thoughts and emotions can all be observed, just as if observing someone else's. The conclusions drawn in this way are objective and truthful, impartial and upright. Thus one comes to understand the wholesome and unwholesome nature of one's own thoughts, and will consciously or unconsciously correct and transform one's own mind. If mind has separated from mind, seeing the path is not far off.
All of these observations belong to the contemplation of the four foundations of mindfulness. Regardless of whether a person has studied and cultivated the four foundations of mindfulness, as long as one can observe truthfully, one will unknowingly enter the contemplative practice of the four foundations of mindfulness—body, feeling, mind, and dharmas—and only afterward can one see the path. The contemplation of the four foundations of mindfulness is the contemplative practice that must be cultivated before seeing the path; therefore the contemplative practice of any Hīnayāna dharma cannot be separated from the contemplation of the four foundations of mindfulness. The contemplation of the four foundations of mindfulness is the expedient method, the swift method, for reaching liberation, and it is also the expedient and swift dharma gate leading to the Mahāyāna.

Ru Chun: This disciple has observed that at certain times when afflictive habits arise, it is like using fire to ignite wet firewood—the flame flickers for a moment, but no true fire is produced. Does this mean there is now a slight separation between the mind and the afflictions?

Assessment: Because the mind has seen the five-aggregate world as empty, the afflictions are no longer so many and so heavy. It is like wet firewood: when it meets a spark, because water overcomes fire, the causes for kindling fire are not complete, so fire cannot be lit; afflictive karmic actions naturally do not arise, and afflictive karma cannot be created. What is the cause for kindling fire? It is taking the five aggregates as real and truly existent, taking them as "mine." When one observes that the five aggregates are not self and not real, they become unrelated to oneself—then what reason is there to kindle fire?

Ru Chun: It is indeed so. Without needing the mind consciousness to instruct it, the fire simply cannot be lit, naturally and spontaneously. The state of mind is fairly stable and peaceful; it is just that sometimes a strong sense of renunciation suddenly arises, wishing one could immediately leave the present environment for a place isolated from the world, requiring no food or drink, no attendants, and no various worries. I always want to find some place like deep mountains and old forests to stay alone in quiet purity. But wanting is one thing—reality does not allow it, so I can only stay honestly and helplessly at home, passing the days.