I have quotes from Culadasa and Rob Burbea, which I will omit for brevity, where they both say the formless realms are actually perspectives on or variants of the fourth jhāna. I am under the impression that the Buddha says something along these lines in the suttas, but I cannot find a reference. Any ideas?
The fourth jhana forms a basis through pure equanimity for the subsequent four formless attainments:
Also MN 111
The four formless attainments are separate from the four jhanas.
Advanced study: There is an alternative route to the four formless attainments in the suttas called 'the eight emancipations (vimokkha), ’ where visual subjects, form and colour, constitute the approach to the formless. (DN 15, MN 77, MN 137).
This contrast of opposites (form/formless) is a necessary strategy to be understood to comprehend the teaching in general :
“Monk, the property of light is discerned in dependence on darkness. The property of beauty is discerned in dependence on the unattractive.” (SN 14.11).
Indeed. I’m not sure it’s right to say there is “alternative route”, though. Traditionally the vimokhas (and other alternative frameworks) have been understood as different ways of talking about jhana experiences, and I see no reason to doubt that this is correct.
One difference between academic researchers and meditators that I find is that academics tend to bounce off the letter of the text and assume that a difference in letter means a difference in meaning. Meditators see all descriptions of meditation, rather, as different perspectives on meditation, none of which fully define or capture the experience.
The first three emancipations are relevant here:
“Possessed of form, one sees forms. This is the first emancipation.
Not percipient of form internally, one sees forms externally. This is the second emancipation.
One is intent only on the beautiful (brahma viharas). This is the third emancipation.”—-Thanissaro
“According to an explanation given in the Patisambhidāmagga, the first deliverance involves developing the perception of a colour like blue, yellow, red, or white. This colour, or more precisely the `sign’ of this colour, the nimitta, is at first to be given attention “internally” on oneself, ajjhatta paccatta. Once this has been well developed the same coloured sign is to be given attention “externally”, bahiddhā, leading to a perception of materiality in terms of the respective colour internally as well as externally (PaJis II 38).
Next, according to the Atthasālinī’s explanation, the jhānic vision of these colours should be developed externally by way of a kasina meditation object. The second of the eight deliverances would then represent the case of someone who does not develop the internal vision of colours described under the first deliverance, but instead directly proceeds to develop the vision of these colours with the help of an external device.” —-Analayo
I use this method for samatha practice and developed it independently early on derived from fine art, which is a western expression of deva levels of consciousness (upper sensuous realm), not aware of the eight emancipations at that time. I claim no more than access concentration, but from that can see that although it does lead to jhanic experiences, the very different subject matter definitely warrants this being classed as an alternative path.
Practitioners who are temperamentally unsuited to the breath but have visual awareness would find this method more suitable. The difference is it relies on developing the nimitta rather than piti, which is a visualization skill.
The multiple practices detailed in the suttas are informative in their diversity. For example, AN8.63 has no mention of either jhana or formless. And MN8 cautions against sole reliance on form and formless meditations. Studying all together reveals the subtlety of practice.
Indeed! It is part and parcel of the Abhidhamma project (in the broad sense) to amalgamate all the different teachings. But the suttas are much more nuanced and contextual.