From Nagajuna’s MMK, Chapter 3 - The examination of the Senses. The commentary/errors/explanations are my own and hence should be taken with large grains of salt.
3.1
Seeing, hearing, smelling,
Tasting, touching, and mind
Are the six faculties.
Their spheres are the visible objects, etc.
The chapter starts out with an assertion (verse 3.1) made by those objecting to Nagarjuna. They assert truthfully that the Teacher taught the six sense bases. From this they infer the existence of sensed objects. If sensed objects don’t exist, then how could the six sense bases exist in their absence? Hopefully, you can already see this as a corollary to your presentation above where the existence of the knower is inferred from the known aka nibbana.
3.2
That very seeing does not see
Itself at all.
How can something that cannot see itself
See another?
This is Nagarjuna’s reply. He turns the statement around on its head and points out that the sense base of seeing cannot see itself. Not seeing itself; upon what can the inference that seeing exists be based? When seeing tries to analyse (or see) itself it comes up empty. The ways of knowing - the six sense bases - are not able to verify themselves. A sword cannot cut itself. A fingertip cannot touch itself. The six sense bases cannot know themselves.
3.4
When there is not the slightest seeing,
There is no seer.
How could it makes sense to say
That in virtue of seeing, it sees?
Without establishing seeing or the other ways of knowing how is it possible to establish a seer or a knower? In the absence of knowing how can a knower be known?
Furthermore, what is this “it” that sees? This “it” is also maintained to exist in the absence of seeing - due to the dichotomization of the six ways of knowing - so it is not appropriate to establish the existence of “it” by virtue of seeing, even if seeing could be established. This is a powerful refutation to my mind.
3.5
Seeing does not see.
Nonseeing does not see.
Through seeing itself
The analysis of the seer is understood.
The word seeing describes an action. The eye is posited as the agent of this action. The agent has neither the nature of the action nor the absence of the nature of the action.
If it has the nature of the action, then “it” (the eye) cannot be known by virtue of seeing; if it could, then two actions (one for seeing itself and another for seeing the other) would be necessary and hence two agents which leads to infinite regress. If it doesn’t have the nature of the action, then what’s left is an eye that is void of the nature of seeing. If what is void of the nature of seeing could see, then even fingertips could see. Neither is appropriate; this is another way of understanding that, “in virtue of seeing, it sees” is not appropriate.
We can understand, “through seeing itself, the analysis of the seer is understood” as a poetic refutation of the seer through verse. ‘Seeing itself’ has been refuted. Through analysis proving so, the seer (or lack thereof) can be understood.
3.6
Without detachment from vision there is no seer.
Nor is there a seer detached from it.
Without a seer
How can there be seeing or the seen?
Either a seer can be posited to exist in dependence upon seeing or independent of seeing. A dependent seer cannot be said to exist in the absence of seeing. An independent seer cannot be posited to exist merely on the presence of seeing. A dependent seer that cannot see itself can thus not be said to exist. An independent seer can only be known to exist by seeing itself. Neither is found. If neither a dependent seer nor an independent seer can be posited to exist, then how can seeing be posited or the seen posited?
3.7
From the nonexistence of seeing and the seen it follows that
The four—consciousness, etc.—do not exist.
Since this is the case, how could such things as
The appropriator exist?
The same difficulties we have positing the existence of the seer, the seeing, and the seen can be applied to all of the six sense bases and their objects. The appropriator of the six sense bases also runs into the same difficulties and cannot be posited to exist.
3.8
Through the explanation of seeing,
Hearing, smelling, tasting, touching, and mind,
Hearer and sound, etc.,
Should also be understood.
All of the above analysis applies equally well to the rest of the six sense bases. Undergoing this analysis it can be seen that all six sense bases are void, hollow and completely insubstantial just as the Teacher has said.
‘Empty village’ is a term for the six interior sense fields. If an astute, competent, clever person investigates this in relation to the eye, it appears vacant, hollow, and empty. If an astute, competent, clever person investigates this in relation to the ear … nose … tongue … body … mind, it appears vacant, hollow, and empty.
SN 35.238
