It seems people enjoyed the quotes from primary sources, so it might also be interesting to contrast the presentation in the Ratnagotravibhāga
with that of the Mūlamadhyamakakārikā
, the root text of the Madhyamaka school. The MMK has 2 whole chapters (16 & 25) entirely dedicated to your exact question, so there's a lot of material to choose from. I picked the first 3 verses of chapter 25 "An Investigation of Nirvana", together with Candrakīrti's explanations from the only surviving Sanskrit commentary, the Prasannapadā
. Unfortunately this is a bit longer than the quotes from the RGV, because the MMK tends to build its arguments over multiple verses, & I couldn't really cut it down to just a short passage.
Like almost all the chapters of the MMK, it begins with a hypothetical opponent objecting in verse 25.1 that if things were empty, some crucial element of Buddhist faith becomes untenable. Nāgārjuna then turns the table in verse 25.2, saying that the fault the opponent attributes to him actually applies to the opponent himself. In verse 25.3 he gives his own position.
The hypothetical opponent is a traditional follower of Abhidharma, who gives an explanation of nirvana similar to Jetavan earlier in this thread. Note that the 2 quotes he supplies in support of his position are both from Pali suttas, although in this case they're quoted from Hybrid Sanskrit sources.
The argument hinges on the idea that if things had "real natures" (svabhāva, often translated very literally, but not very meaningfully, as "own-being"), they could never change. This idea is developed earlier in the text, so here Candrakīrti simply assumes the argument is understood. The commentary also assumes a huge amount of technical vocabulary related to the aggregates, the conceptualizing process, karma & the afflictions, etc., but it's not really necessary to get the gist of things, & I haven't tried to translate all of these with separate English words.
I won't quote the Sanskrit this time as it's too long. It can be found here (Pp_227--Pp_230).
Bold indicates the root text, the rest is Candrakīrti's commentary. Slash marks indicate lines of Sanskrit verse.If all this is empty, nothing begins or ends. /
What then is eliminated, or what ceases, for you to assert nirvana? //25.1//
[The Opponent:] In this religion, the Blessed One taught two kinds of nirvana for those who dwell in celibacy, who follow the Thus Gone's instructions, and who are yoked to the practice of the Dharma in accordance with the Dharma: 1) nirvana with remaining accretions [sopadhiśeṣa], and 2) without remaining accretions [nirupadhiśeṣa]. Concerning this terminology, the word "accretions" refers to the five addictive aggregates which are the basis for the designation of a Self, because the love of Self accretes to them. The accretions themselves remain; therefore it is called nirvana with remaining accretions. The aggregates alone remain, completely devoid of the thieves known as the afflictions, such as the view of the real body [satkāyadṛṣṭi], similar to a village surviving after a band of robbers has been completely cast out. This is nirvana with remaining accretions. The nirvana where even the five aggregates don't exist is called "nirvana without remaining accretions", in reference to the accretions being gone, similar to the destruction of both the band of robbers and the village itself. Concerning this, it is said [in the Dabba-sutta Ud 8.9]-
The body is broken, cognition ended, all sensation burned out /
Karmic formations stilled, consciousness has come to an end //
and [in the Mahāparinibbāna-sutta DN ii; this the Buddha's attendant Anuruddha's famous verse at the death of the Buddha]-
With unbent body, he remained resolute in the face of painful sensation /
The liberation of his mind is like the extinguishing of a flame //
Thus, nirvana without remaining accretions is understood to follow from the cessation of the aggregates. How then can the two kinds of nirvana be accepted? When the cessation of afflictions and aggregates is real. If, however, all this is empty, and nothing whatsoever arises or ceases, then there are no afflictions or aggregates whose cessation would be nirvana. Therefore things must have real natures.
In response to this it is said: If we were to accept real natures, then
If all this is not empty, nothing begins or ends. /
What then is eliminated, or what ceases, for you to assert nirvana? //25.2//
As a real nature is permanent, how could afflictions and aggregates established with real natures ever be extinguished? How then could there be a nirvana based on their extinction? Therefore nirvana is impossible for those who proclaim real natures. Nor do those who proclaim emptiness assert that nirvana is defined as the extinction of the aggregates or afflictions. Therefore this fault does not apply to those who proclaim emptiness.
[Opponent:] If those who proclaim emptiness do not assert that nirvana is defined as the extinction of the afflictions or the aggregates, how do they define it? [Response] It is said:
Without elimination, without attainment, not cut off, not eternal, /
that is said to be unceasing and unarisen nirvana. //25.3//
It is not eliminated like desire and the other afflictions, nor obtained like the fruit of spiritual practice, nor cut off like the aggregates, nor permanent like the non-empty; this is called naturally unceasing and unarisen "nirvana", defined as the pacification of all conceptual elaboration. In such a state of non-elaboration, how could there be the conception of afflictions, whose elimination would be nirvana? How could there be conception of aggregates, whose cessation would be nirvana? For to the extent that conceptions proliferate, there can be no realization of nirvana, as the realization of nirvana is the very dissolution of all conceptual proliferations.
"Very well then," [says the opponent], "although there are no afflictions or aggregates in nirvana, they do exist prior to nirvana. Therefore it is after their dissolution that nirvana will exist." [Response] This grasping is to be abandoned, as something which existed with real nature before nirvana could not later be made non-existent. Therefore one who desires nirvana should abandond this notion. As [Nāgārjuna] will later say [in verse 25.20]:
There is not the slightest difference whatsoever /
between the sides of nirvana and samsara //
Thus it should be understood that in nirvana there is nothing whatsoever eliminated, and nothing whatsoever ceases. Therefore nirvana has the nature of the complete dissolution of all conceptualization. As was said by the Blessed One [in the Samādhirāja-sūtra]:
In extinction dharmas are not dharmas; what does not exist in this state does not exist at all. /
For those who imagine, "This exists, this does not exist," and who act accordingly, suffering will not be stilled. //
This verse means: In extinction, i.e. nirvana without remainder, there is no existence, because of the complete dissolution of the aggregates, or dharmas characterized by affliction, karma, and birth, old age, sickness, and death. This all sides agree on. But the dharmas which do not exist in nirvana never existed at all, just like the fear of a snake imposed on a rope observed in the dark, after a lamp is lit. The dharmas characterized by affliction, karma, and birth, old age, sickness, and death never really existed in the state of samsara either, just as the rope in the state of darkness was never truly a snake, because neither one's hands in darkness nor one's eyes in light experience the rope as a real snake. If [the opponent] were to object, "Why then is there samsara?" it is said [in response], "Although they are unreal, things appear as real to child-like ordinary beings seized by grasping to "Me and Mine" as real, similar to unreal hairs, etc. appearing in the vision of people with cataracts."
... [there follows a section on the different Buddhist and non-Buddhist philosophical schools implied by the phrase "those who imagine 'This exists, this does not exist' "]
Thus [in the Ratnaguṇasaṃcaya-gāthā]
As someone can be struck down by the mere suspicion
that he has ingested poison, even though no poison entered his stomach /
Just so a fool thinks "I am this, this is mine"
and by this unreal notion is born and dies forever. //
Thus it should be understood that in nirvana nothing whatsoever is eliminated, and nothing whatsoever ceases. Therefore nirvana simply has the nature of the ending of all conceptions. As it is said in the Ārya-ratnāvalī-
Nirvana is not even non-existence, how then can it be existence? /
Nirvana is the end of the conceit of existence and non-existence. //