SuttaCentral
If “consciousness” is what knows the rising and falling of the other 4 aggregates (nama-rupa - right?), then what knows the rising and falling of “consciousness”?
I’m thinking here of the simile of the two sheaths of grass leaning against one another. nama-rupa on one side and consciousness on the other.
Or … is the “knowing” an emergent property of the rising of the two sides together? If so, what is that called (in Pali)?
Or … Am I misunderstanding this.
Okay! Welcome to the most confusing and misunderstood chapter of the teaching! 
Viññana here is translated as consciousness but it is referring, imho, to something other than what we often call “consciousness” in English! It is not a reflective or introspective awareness, but rather the basic evolutionary power of recognition and discrimination which allows you to discern difference and variety across all experience. So it is absolutely necessary for self-awareness but it is not itself self-awareness!
Self-awareness, that which knows and recognises the five groups in the way you describe - that is for ever a nameless miracle! It is called Amun, it is called God, love, redemption, Sophia, soul, spirit, Psyche, transcendence, and many other appellations, including “consciousness”! In Dhamma, down to earth, we speak of sati & pañña!
It is our only true freedom, there’s non other! 
The Buddha has said that all that is (mistakenly) considered the self, is in the five aggregates and he showed how the five aggregates arise in the process of perceiving a stimulus from the six sense doors. This he said, then is the world, the all, if I am not mistaken. In other words everything we know if made up of these phenomena. Even intellectually we can see that they last only a moment, so that other factors like labelling, intending, feeling can arise quickly and is perceived to ‘belong’ to that object which is being focused upon now. They also equally come to an end, so that another stimuli (sound or sensation) can take its place, from a different sense door.
Having seen this process in detail, it becomes apparent that there is no other ‘hidden’ process to observe something. By the process of inference, in insight meditation, it is apparent that this process is applicable to all processes of observing, including the one that is happening now- i.e. the process of observation is also yet another replica of the same process that is being used to observe the aggregates now.
I.e. there is no observer or any universal consciousness… that belongs clearly, and unfortunately, in Mahayana. All that is there that could be considered as an observer is in the five aggregates- no other consciousness is mentioned in the five aggregates. It is the same consciousness that arises at each of the six sense doors. It is causally arisen by mental and material objects presenting at the sense doors -i.e. the simile of the reeds.
with metta
p.s.- please excuse my i.e.s -bad writing habit, but useful…!
Hi @Mat (or anyone),
can you point me in the direction of where this process is described in the suttas? Is it in several overlapping suttas? I don’t think I have all the pieces of the puzzle yet. Is there a contemporary commentary around this process?
This is found in several suttas and is a core EBT concept. Most of it can be found conveniently in one sutta below:
"Dependent on the eye & forms there arises consciousness at the eye. The meeting of the three is contact. With contact as a requisite condition there is feeling. With feeling as a requisite condition there is craving [broadly Sankhara or volitional fabrications]. ". MN148.
This sutta adds the last bit of the puzzle:
“There are these six kinds of perception: the perception of form, the perception of sound, the perception of aroma, the perception of flavor, the perception of tactile sensation, the perception of ideas. And what is the cause by which perception [sanna] comes into play? Contact is the cause by which perception comes into play”. AN6.63
with metta