Theravada and Nagarjuna

Officially the Theravadans means the people who like the vinaya & suttas in pali, and sometimes their parallel in chinese and so on, and also the same for their abiddhama. Sometimes theravadans are just the people who like the suttas (and the vinaya?).

So for people who like the suttas most, philosophy is useless to reach nibanna. And the fantasy that there is a ''proof of nibanna'' and a ''proof of the wrongness of wrong views (ie not buddhism)'' is complete non-sense, ie only a fantasy. At best it will be the people who like the abidhamma, who enjoy mental gymanistics a bit more, but then reading another book from some indian intellectual wherein he wrote his speculations on whatever was buddhism at the time and trying to ''refute'' whatever the Shravakas had written in their own abidhamma is usless to them, since they think their abidhamma is already good enough to reach nibanna.

More generally, what is even a ''proof'' in philsophy? In maths they use ''proof'' too, but in philsophy people keep saying such claim is an ''argument'' and such string of arguments is a ''proof of some other claim'' but so far intellectuals do not even agree on what a proof is in philsophy. And how a string of sentences in some language would even be a proof of nibanna?

The buddha said that the only good use of ''mano'' is yoniso manisakara , which just means thinking a lot about the dhamma, but in this way : ''thinking about what is the fuels the arising of sensual desire'' https://suttacentral.net/sn46.51/en/sujato and so on, so just dependant origination. And in Mahyana, they confuse dependant origination with interconnectenedss already, so they struggle a lot on the dhamma.

And it is this proper attention, ie comparing your life with whatever the buddha calls the good life, that is supposed, sooner or later, to get you into samadhi, and then it is right samadhi which will get you to nibanna. https://suttacentral.net/sn9.11/en/sujato

Thinking about the Teacher, the teaching, the Saṅgha, and your own ethics, you’ll find gladness, and rapture and bliss as well, no doubt. And when you’re full of joy, you’ll make an end to suffering.”

Officially, the ''proper attention'' has faith for condition

And what is the fuel for mindfulness and situational awareness? You should say: ‘Proper attention.’ I say that proper attention is fueled by something, it’s not unfueled. And what is the fuel for proper attention? You should say: ‘Faith.’ I say that faith is fueled by something, it’s not unfueled. And what is the fuel for faith? You should say: ‘Listening to the true teaching.’ I say that listening to the true teaching is fueled by something, it’s not unfueled. And what is the fuel for listening to the true teaching? You should say: ‘Associating with good people.’

https://suttacentral.net/an10.61/en/sujato

So none of the mental proliferations of indian intellectuals fit in the dhamma.

Bhikkhu K. Ñāṇananda, a Theravādin monk, did mention him from time to time. From Questions & Answers On Dhamma :

“The five ascetics were given a teaching based on the ethical middle path, avoiding the two extremes of kāmasukhal- likānuyoga and attakilamathānuyoga. But the middle path of right view is found in the Kaccānagotta Sutta, beautifully used by Ven. Nāgārjuna. When the Theravadins got engrossed with the Abhidhamma they forgot about it. The Mādhyamikas were alert enough to give it the attention it deserved.

(...)

“I didn’t quote from the Mahāyāna texts in the Nibbāna sermons,” he says, “because there was no need. All that was needed was already found in the Suttas. Teachers like Nāgārjuna brought to light what was already there but was hidden from view. Unfortunately his later followers turned it in to a vāda.”

He goes on to quote two of his favourite verses from Ven. Nāgārjuna’s Mūlamādhyamakakārikā (as usual, from memory):

Śūnyatā sarva-dṛṣtīnaṃ proktā niḥsaranaṃ jinaiḥ, yeṣāṃ śūnyatā-dṛṣtis tān asādhyān babhāṣire [MK 13.8] The Victorious Ones have declared that emptiness is the relinquishing of all views. Those who are possessed of the view of emptiness are said to be incorrigible.

Sarva-dṛṣti-prahāṇāya yaḥ saddharmam adeśayat, anukampam upādāya taṃ namasyāmi gautamaṃ I reverently bow to Gautama who, out of compassion, has taught the doctrine in order to relinquish all views. – [MK 26.30]

Bhante doesn’t bother translating the verses; the ones provided above are by David Kalupahana.;

“When I first read the Kārikā I too was doubting Ven. Nāgārjuna’s sanity” he laughs. “But the work needs to be understood in the context. He was taking a jab at the Sarvāstivādins. To be honest, even the others deserve the rebuke, although they now try to get away by using Sarvāstivāda as an excuse. How skilled Ven. Nāgārjuna must have been, to compose those verses so elegantly and filling them with so much meaning, like the Dhammapada verses. It’s quite amazing. This has been rightly understood by Prof. Kalupahana.”

Prof. David J. Kalupahana is an eminent Sri Lankan scholar who stirred up another controversy when he portrayed Ven. Nāgārjuna as a reformist trying to resurrect early Buddhist teachings. He had been a lecturer during Bhante Ñāṇananda’s university days as a layman at Peradeniya.

(...)

“Ven. Nāgārjuna was right: at the end, all is empty. We are not willing to accept that existence is a perversion. Existence is suffering precisely because it is a perversion.”

See also this, this and this (from a more Early Buddhist Texts perspective than Theravādin, however).

OP:

In his Fundamental Verses Nagarjuna demonstrates the absurdity of positive or extreme metaphysical positions.

Do Theravadans accept this proof as valid and sound?

Personally, I am not familiar with Nagarjuna's works regarding the absurdity of positive or extreme metaphysical positions.

Theravadans generally accept the absurdity of extreme metaphysical positions, because they accept the absurdity of all metaphysics, due to the following statements in the suttas.

So, I suppose we can say that Theravadans agree with Nagarjuna?

From Acintita Sutta:

"Conjecture about [the origin, etc., of] the world is an unconjecturable that is not to be conjectured about, that would bring madness & vexation to anyone who conjectured about it.

From Sabba Sutta:

"Monks, I will teach you the All. Listen & pay close attention. I will speak."

"As you say, lord," the monks responded.

The Blessed One said, "What is the All? Simply the eye & forms, ear & sounds, nose & aromas, tongue & flavors, body & tactile sensations, intellect & ideas. This, monks, is called the All. Anyone who would say, 'Repudiating this All, I will describe another,' if questioned on what exactly might be the grounds for his statement, would be unable to explain, and furthermore, would be put to grief. Why? Because it lies beyond range."

To the Buddha, pragmatism was more important than metaphysics. Please see the Parable of the Poisoned Arrow.

You are referring to a full book comprising of 27 chapters, with at least ten different translations. That makes it hard to know what the "positive or extreme metaphysical positions" are for someone unfamiliar with his writings, so the question may be difficult to answer without specific references.

Anyway, with all due respect for Nagarjuna, from a fundamentalist approach here are some suggestions for demarcation criterias from the nikayas.

AN 4.77:

Mendicants, these four things are unthinkable. They should not be thought about, and anyone who tries to think about them will go mad or get frustrated. What four?

The scope of the Buddhas …

The scope of one in absorption …

The results of deeds …

Speculation about the world …

These are the four unthinkable things. They should not be thought about, and anyone who tries to think about them will go mad or get frustrated.

https://suttacentral.net/an4.77/en/sujato

MN 63:

These positions that are undeclared, set aside, discarded by the Blessed One — 'The cosmos is eternal,' 'The cosmos is not eternal,' 'The cosmos is finite,' 'The cosmos is infinite,' 'The soul & the body are the same,' 'The soul is one thing and the body another,' 'After death a Tathagata exists,' 'After death a Tathagata does not exist,' 'After death a Tathagata both exists & does not exist,' 'After death a Tathagata neither exists nor does not exist' — I don't approve, I don't accept that the Blessed One has not declared them to me. I'll go ask the Blessed One about this matter. If he declares to me that 'The cosmos is eternal,' that 'The cosmos is not eternal,' that 'The cosmos is finite,' that 'The cosmos is infinite,' that 'The soul & the body are the same,' that 'The soul is one thing and the body another,' that 'After death a Tathagata exists,' that 'After death a Tathagata does not exist,' that 'After death a Tathagata both exists & does not exist,' or that 'After death a Tathagata neither exists nor does not exist,' then I will live the holy life under him. If he does not declare to me that 'The cosmos is eternal,'... or that 'After death a Tathagata neither exists nor does not exist,' then I will renounce the training and return to the lower life.

https://www.accesstoinsight.org/tipitaka/mn/mn.063.than.html

MN 2:

'Did I exist in the past? Did I not exist in the past? Who was I in the past? How was I in the past? In the past, who had been I and who was I [in the subsequent existence]? Will I exist in the future? Will I not exist in the future? Who will I be in the future? How will I be in the future? In the future, having been who, who will I be?'

Also as regards the present, uncertainty arises in him thus: 'Do I exist? Do I not exist? Who am I? How am I? From where has this soul come? Where will this soul go?'

In a person who thus considers improperly there arises one of the six [wrong] views. The view 'I have self' arises in him really and firmly. Or, the view 'I have no self' arises in him really and firmly. Or, the view 'I perceive self through self' arises in him really and firmly. Or, the view 'I perceive non-self through self' arises in him really and firmly. Or, the view 'I perceive self through non-self' arises in him really and firmly. Or, he has the view thus: 'That self of mine speaks, knows and experiences the results of wholesome and unwholesome actions. That self of mine is permanent, stable, durable, incorruptible and will be eternal like all things permanent.'

https://www.accesstoinsight.org/tipitaka/mn/mn.002.bpit.html

Of course traditionally Theravada Buddhism has regarded Nagarjuna as not one of its own. He has too long been claimed by Mahayana to expect otherwise. But some relatively recent scholarship regards him as a transitional figure, with close affinities -- as you suspect -- to Early Buddhism. In fact, a very strong case can be made that he regarded himself as a defender of Gautama as recorded in the suttas. His opponents were not in the suttas, but in the Abhidharma philosophy that dates from several centuries after Gautama and several centuries before Mahayana.

A.K. Warder's rather monumental Indian Buddhism argues that Nagarjuna was closer to Gautama than the Mahayana, and blurs the distinction.

David Kalupauhana's Nagarjuna: Philosophy of the Middleway is an eminently scholarly translation and commentary on Nagarjuna's Mulamadhyamakakarika which argues that Nagarjuna was not Mahayanist at all, and in fact makes the case that the Karika itself is a commentary on the Kaccayanagotta Sutta, upholding Gautama's view of the middle way between "eternalism" and "nihilism."

You can find Velez de Cea, “Emptiness in the Pali Suttas and the question of Nagarjuna's orthodoxy.” (Philosophy East and West 55(4) October 2005) on line. Here, parallels between Nagarjuna and the suttas are gathered, and Nagarjuna's roots in the suttas is demonstrated.

In the Sunna Sutta, Gautama is asked: “In what respect is it said that the world is empty?" and answers; "Insofar as it is empty of a self or of anything pertaining to a self.” This is pretty much Nagarjuna's view. In the Sunyatatasaptati (Emptiness: The Seventy Stanzas), he writes that “since the intrinsic being [self-nature] of all entities does not exist . . . therefore they are empty."

The reason I have this at my fingertips is because I've been spending my time in COVID lock-down writing a piece on Nagarjuna that argues that he believes he is upholding Gautama's Dharma. Although it's dressed up, it was really written just to pass the time, but I'll put it on line for you, and in fact would be pleased if you read it, and comment if you wish. It will be at

Reading Nagarjuna -- A rendition of Chapters 1, 24, and 25 of The Mulamadhyamakakarika for Students of the Buddha's Dharma

You are right that Nagarjuna and Gautama both reject the unanswerable questions" about Ultimate Realities (and N. warns that only fools confuse emptiness with the Absolute), believing, in distinction to almost every religion, that answers to metaphysical questions are not necessary for "salvation." As I suspect you know, the Cula-Malunkyovada Sutta asks "did I ever say to you . . . live the holy life under me, and I will declare to you that 'The cosmos is eternal,' or 'The cosmos is not eternal . . . [etc.]. The final chapter of the Karika, “Examination of Views,” is concerned entirely with the unanswered questions contained in this and other suttas. The last verse of the Karika states: “I reverently bow down to Gautama who, out of compassion, has taught the true doctrine in order to relinquish all views.” The "views" he refers to are the unanswered questions of the suttas. No more no less.

I think it is clear from the suttas and Karika that there are 2 reasons for rejecting the unanswered questions -lst because they are improper questions in the sense that they have no answers, they are metaphysical speculations 2nd because they do help --- and N. echoes G. on both counts.

You can certainly, IMO, like me, be a follower of the Buddhism of the suttas and accept almost all of N.'s Karika. But whether a strict Theravedan would agree, I cannot say.