The all-base consciousness is the general basis for the whole mind, and thus for all of the consciousnesses. Though each of the particular consciousnesses has its own specific functions and defining characteristics, you can, from the absolute point of view, only talk of the mind as a singularity. The mind is one; its essence is one. It has its specific defining characteristics and functions, but only a single expression which is clear and cognizing.
When the eyes see an object and the mind immediately apprehends that object without having to check or confirm it through any other process, or, when the mind consciousness understands the ear consciousness immediately, a connection of mutuality is indicated. Though the mind is divided into particular categories, the connection comes about due to the single nature of the all-base consciousness.
Being the basis for all aspects of the mind, it is designated as the eighth consciousness. The all -base consciousness expresses itself in two different ways.
Firstly, it is the ‘all-base that seizes karmic imprints’. That means all karmic imprints, such as the perceptions of the eyes, ears, nose, tongue, or those of the body , as well as all mental activities including those of a studious nature, are grasped by the all-base so that they will not be forgotten. In this way memories are made: something is seized and not thereafter forgotten. None of the consciousnesses of the six collections can seize their imprints. These consciousnesses dissolve as soon as they arise. However, the corresponding karmic imprints are stored within the all-base. They are collected there, and thus not forgotten. If we learn something today the corresponding information is stored in the form of karmic imprints within the all-base, and this is why it is possible to remember it tomorrow or at a later date. In this respect— that of the functions of seizing, storing , and not thereafter forgetting— the all-base consciousness is called the ‘all-base that seizes karmic imprints’.
The second aspect of the all-base consciousness is called the ‘all-base of complete ripening’. This designates the possibility of allowing the karmic imprints that were once stored in the mind to reappear again. The future reappearance of the karmic imprints is the function of the all-base of complete ripening.
Generally, as is the case for perception, it seems as if the sense organs and their corresponding faculties were located inside the body and the perceived objects outside. We take it for granted that, for example, the eye and the eye faculty are inside and the perceived form, the eye object, outside. While we are engaged in the act of seeing, the eye seems to look at the object, a form that is present outside. We therefore think that forms, sounds, smells, tastes, and tangible objects are externally present and that their corresponding consciousnesses are internal.
From the Buddhist point of view this is certainly not the case. In our view the eye consciousness merely perceives a mental image of the form to be perceived. This form is not really external, but merely mental. The same is the case for all other sense objects; the mind itself appears in their form. Other than that they don’t exist externally at all. Therefore we teach that all appearances are mind. If we ask ourselves how the objects appear, we can say that it is the all-base consciousness itself that appears in the form of these objects, which are then perceived through the perspective of the sense consciousnesses . This is why this aspect is called the ‘all-base of complete ripening’.
When we teach that all appearances are just appearances of the mind, it often happens that beginners cannot put their trust in that. This is because our karmic imprints have been stored since beginningless time, one of which is the assumption that the sense objects are external and the mind internal. With precisely this imprint we have a difficult time understanding that the objects appear as an image of the mind.
In order to clarify this point through careful analysis, we can take dreaming as an example. In the context of a dream mountains, houses, horses, elephants, and so forth appear to us, and we take it for granted that these appearances are actually present externally. We think that the mountain is actually there. The same is valid for the house in a dream: we think it is really present. In reality, however, there does not exist the slightest trace of any house or mountain. They are not actually there, but still they appear as if they were.
So where is it that they appear? They appear in the essence of the mind.
Since every one of us has our individual experiences in dreams, it is easy for us to understand that the dream objects merely appear within the mind. As with the dream objects, in this example, the same applies to the whole of reality while we are not dreaming. We assume the appearances of objects in ordinary life, when we are not dreaming , are indubitably there. However, they are not truly present externally. They appear on the basis of the inner mind, in the same way as appearances in a dream. The karmic imprints once stored in the all-base reawaken, emerge, and appear to us.
Rinpoche, Khenchen Thrangu (2007-03-15). Everyday Consciousness and Primordial Awareness (p.34- 37). Shambhala Publications. Kindle Edition.