Thank you for the extended notes on DN 15!
At the nāmarūpapaccayā phasso nidāna, the note says:
Nowhere else is this condition expressed in this way, and the sutta goes on to develop a unique analysis to explain it.
However, this is unclear. At Snp 4.11, the sutta says that nāmarūpa is the condition for phassa directly, and at SN 12.19 it is implicit in the text. At SN 1.23 and SN 7.6 we see some echoes of the same ideas in verse. Point being: it is not that these ideas occur nowhere else. Maybe making it a bit more clear that the explanation is unique, but not the condition (name-&-form → contact) itself?
Thank you also for adding notes to the eight liberations as requested, bhante! I did have some feedback content wise here though as well.
I feel that the stations of consciousness can be quite unclear/ambiguous, and several teachers have been relatively perplexed by them IME. I’m thinking particularly of the ‘unified/diverse perception’ or body part. Maybe you could explain a bit what exactly it means for the lower brahmā deities to have unified perception, and the higher ābhassara deities to have diverse perception but be unified in body?
I also think that there is then a clear connection to the eight liberations that was overlooked in the notes on them. The first three were simply equated with the four jhānas and the first two were just different equally valid forms of meditation. But the second liberations is, in my opinion, clearly meant to be a state liberated of something not in the first. In other words, there is a clear progression there (verified also by the ‘forward and reverse order’ description of attaining them). So one should be able to progress from the first to the second via a natural refinement of the meditation, not just a huge switch in theme.
DN 15 is relatively unique in defining the paññāvimutta arahant by their wisdom-faculty in terms of the 7 stations / 2 bases of consciousness. It is by understanding the conditionality of dependent origination and the gratif./danger/etc. that one’s wisdom sees through all of this. The ubhatobhāgavimutta arahant on the other hand has direct personal experience with the various stations of consciousness, and their personal attainment propels insight into these states forward, culminating in the stilling of sankhārā into the nirodha samāpatti.
At SN 14.11, the Buddha gives a very similar list of meditative / conscious states. The first two are light (ābhādhātu) and then beauty (subhadhātu), then infinite space. There is a clear similarity between this and the seven stations (abhassara, subhakinha, infinite space) as well as the eight liberations (seeing external forms, liberation of the beautiful, infinite space). Notice also that when we tack on the first liberation, it would correspond to the first brahmā station. There is a clear pattern here, and personally I am neither convinced by nor satisfied with an explanation of the eight liberations that tries to externalize them to another tangential schema outside of the context they better belong to.
The other thing I’d point out is that the third liberation cannot be equated with mettā, because this attainment of the beautiful is said to be the culmination of mettā practice, just as infinite space is the culmination of compassion. But clearly infinite space is a different state than compassion. I agree with the note that it must be an exalted, beautiful state (probably equivalent to third jhāna), but this also contributes to the understanding of these states as a progressive climb from one practice, rather than a mere differentiation of technique.
Maybe the progression you were implying was something like: samādhi, but with difference between one’s form and meditation theme → refined into state of light and unity with meditation theme akin to second jhāna → fully settling into that for a deeper state of beauty ? This roughly corresponds to the diversity in body and unity in body scheme of the stations with the difference between meditative visions and one’s own perception of internal form. And maybe the practice is cultivated via mettā to begin with, culminating in the third liberation before moving into the formless as in the description of the culminations of the brahmavihārā? To me it seems that the brahmavihāras (or mettā specifically), asubha, and element contemplation are the main practices associated with the liberations whereby one can move from internal/external → totality → beautiful → formless. Ānāpānasati does not seem to be part of the schema.
Venerable @sujato , would you be willing to re-assess the notes on these? I’m really curious and interested as to what conclusions you come to if you have another opinion on these practices. Personally I’m very interested in pursuing them, but they are not super clear to me. 
Much mettā! 
