How is the Fourth Discourse Connected with Emptiness?

1. Emptiness of Practice in the Middle Way

Practice in the middle way is empty of polar opposite views. In the first turning of the Dharma-wheel those two views are asceticism leading to self-mortification and hedonism leading to meaningless pursuit of pleasure. In the fourth discourse the polar opposite views are eternalism and nihilism, which we have examined (five posts ago) in connection with seeing straight (samyag-dṛṣṭi).

2. Emptiness of the Five Skandhas

As far as I have noticed, the Buddha himself is not recorded in the first four discourses as speaking explicitly of emptiness. Reading between the lines, however, the Buddha in the fourth discourse evidently described habitual doings (saṁskārāḥ, 4th of the 5 skandhas and 2nd link in the 12-fold chain of dependent arising) as empty.

This can be surmised from the question which the Māgādhans ask the Buddha...

Atha khalu teṣāṁ Māgadhakānāṁ brāhmaṇa-gṛhapatikānāṁ etad abhūṣi:

Then this occurred to those devotees and householders of Māgadha:

“Yato kila bho rūpam anātmā,
“Since bodily form, allegedly, is not self,

vedanā saṁjñā saṁskārā vijñānam anātmā,
since feeling, perception, habitual doings, and consciousness are not self,

atha ko tarhi kārako vā kārāpako vā,
then who in that case is the doer, or the agent,

utthāpako vā samutthāpako vā nikṣepako vā,
or the one that gives rise to, or stirs up, or casts off [these habitual doings]?

yo imāṁ saṁskārāṁ ādīyati vā nikṣipati vā,
Who takes up these habitual doings or casts them off?

yasyime saṁskārā śūnyā anātmanīyā, ātmena vā ātmanīyena vā?
For whom – [thinking practically] in terms of the self or of what belongs to the self – are these doings empty and not belonging to a self?

3. Whatever Dependent Arising There Is, We Call That Emptiness 

yaḥ pratītya-samutpādaḥ śūnyatāṁ tāṁ pracakṣmahe |
sā prajñaptir upādāya pratipat saiva madhyamā ||MMK24.18||
Whatever dependent arising there is, we call that emptiness. 

This teaching, when put into practice, is the middle path itself.

4. Emptiness as Realization

It is instructive to note where in the first four discourses two formulae appear: 

(A) Destroyed is (re)birth, lived is the spiritual life, done is what was to be done, no more is there of this mundane state; 

(B) minds, through not clinging, were freed from the polluting influences.

In the second discourse, the Buddha uses formula (A) to describe one who sees that the five skandhas are not self, and thus comes to know liberation. Using formula (B) the text then records that the group-of-five monks' minds, through not clinging, were freed from the polluting influences, so that at that time there were  in the world six arhats (worthy ones, enlightened beings).

In the third discourse, the Buddha similarly uses formula (A), this time to describe one who sees how the world is burning with the fires of passion, hatred, and delusion, and thus comes to know liberation. The text, again using formula (B), then records that one thousand monks' minds, through not clinging, were freed from the polluting influences.

In the fourth discourse, the Buddha again uses formula (A) to describe one who knows that the five skandhas are not self, and who thus, through not clinging, comes completely to quiet. At this point, however, the text does not describe anybody's mind as being freed from the polluting influences. Rather, the Māgadhans, being practical sorts, men of action, express a certain skepticism. How can it be, they seem to ask, that in the dropping off of habitual doings, there is no-one who takes responsibility for the dropping off? In actual practice, how can there be no practitioner?

It is in response to this doubt that the Buddha goes into detail into what sense saṁskārāḥ, habitual doings, are empty. 

The teaching of 12-fold dependent arising in the fourth discourse is therefore a clarification of the teaching of the emptiness of the five skandhas which was the subject of the second discourse. 

At the same time, because habitual doings are the 2nd link in the 12-fold chain of dependent arising of suffering, this same teaching of dependent arising is a clarification of the four noble truths – the subject of the first turning of the wheel of Dharma. 

What strikes me as interesting is that at the end of this exposition of 12-fold dependent arising, as also at the end of the first turning of the Dharma-wheel, there is mention of attainment of insight (= "the dustless Dharma-eye") and there is mention of being uplifted and greatly rejoicing. But neither in the first nor in the fourth discourse does the text say, using formula (B), that minds, through not clinging, were freed from the polluting influences.

Seeing this, although it has made for progress even slower than the snail's pace at which I translated Aśvaghoṣa's Buddhacarita and Saundarananda, I feel particularly glad that something prompted me,  in laying the ground for the translation of Nāgārjuna's MMK, to go back and study the first four discourses. The cautionary message I take from the above nit-picking is that a translator should never be unduly proud of, and still less cling to, any philosophical understanding, even if it is philosophical understanding of emptiness. 

The point is that, for causing there to be worthy ones in the world, it was sufficient for the Buddha to teach those who had gone forth as monks not to cling to the five skandhas as if they were a self. Seeing the emptiness of the five skandhas, the group-of-five monks in the second discourse and a thousand monks in the third discourse, through not clinging, realized the enlightenment in which the mind is freed from the polluting influences of desire, becoming and ignorance.

For the Buddha, as also one suspects for Nāgārjuna, detailed exposition of 12-fold dependent arising was not so much something they aspired in the first place to teach; the teaching of a 12-fold chain was rather an expedient they resorted to in order to help towards insight people whose eyes were not so free of dust. 

When we see him from this perspective, we might begin to wonder whether those who have looked up to Nāgārjuna as a great philosopher may have in fact been insulting him by describing him in those terms.

A truer way to revere Nāgārjuna might be as a monk, and as a master of sitting-meditation, whose mind, through not clinging, was empty of the polluting influences of desire, becoming, and ignorance. 

Nāgārjuna's purpose in writing MMK, I tentatively submit, might not have been the laying down of the philosphical foundations of Māhayāna Buddhism. His purpose might rather have been compassion for people with more than a little dust on their eye -- like King Bimbisāra and eleven myriad other self-made men of Māgadha who, at the end of the fourth discourse are praised as being possessed of the stainless, dustless, pure Dharma-Eye. None of them is praised yet as having become free, through not clinging, of the polluting influences.

So the implication is that the doings which are the root of saṁsāra they, as ones still steeped in ignorance, continued habitually to do. Therefore they were not free of the divided consciousness which is grounded in habitual doings. They had not dropped off the psycho-physicality which is grounded in divided consciousness. Similarly they were not free of six senses, feeling, and thirsting. Not being free of thirsting, they remained in a state of clinging to the five skandhas of clinging -- like fuel and fire that have taken hold of each other. And so, through clinging, they were not free of the polluting influences. 

The point, to spell it out one more time, mainly for my own benefit, is this: 
Clarification of the various meanings of emptiness, intellectually appealing though that task may be, is not the original aim. If not a dirty trick, it might be a kind of dusty trick. 
The ultimate aim is freedom of the mind, through not clinging, from the polluting influences. 

Hence...

From then on, through investigation of what is, he applies his mind to eradicating the polluting influences, / For on this basis he fully understands suffering and the rest, the four true standpoints: // SN16.3 //This is suffering, which is constant and akin to trouble; this is the cause of suffering, akin to starting it; / This is cessation of suffering, akin to walking away. And this, akin to a refuge, is a peaceable path. // 16.4 // Understanding these noble truths, by a process of reasoning, while getting to know the four as one, / He prevails over all pollutants, by the means of mental development (bhāvanayā), and, on finding peace, is no longer subject to becoming. // SN16.5 // For by failing to wake up and come round to this four, whose substance is the reality of what is, / Humankind goes from existence to existence without finding peace, hoisted in the swing of saṁsāra. // SN16.6 //

"Mental development" in "by the means of mental development" (bhāvanayā) is "cultivation" or "bringing-into-being" in Nāgārjuna's "because of the cultivation of just this wisdom" or "because of the bringing-into-being of just this act of knowing" (jñānasyāsyaiva bhāvanāt)

If we say that "just this wisdom," means the wisdom of emptiness, or the wisdom of dependent arising, in saying that we had better be clear that the wisdom in question is ultimately not intellectual, and not philosophical, but is connected, most fundamentally, with a particular act of knowing -- namely, sitting in full lotus as the dropping off of body and mind. 

Hence, again, in Dogen's words: 

To learn the Buddha's truth is to learn the self. To learn the self-is to forget the self. To forget the self is to be experienced by the myriad dharmas. To be experienced by the myriad dharmas is to let our own body and mind, and the body and mind of the external world, fall away.