Letters of Sri Aurobindo
Fragment ID: 8675
(this fragment is largest or earliest found passage)
Sri Aurobindo — Unknown addressee
Tibetan Yoga 
Evans-Wentz writes: “Thus the Doctrine of the Shūnyatā, underlying the whole of the Prajñā-Pāramitā, posits... an Absolute as inherent in phenomena; for the Absolute is the source and support of phenomena; and, in the last analysis of things, by the Bodhi-illuminated mind, freed of Ignorance, duality vanishes, and there remains but the One in All, the All in One.... This supreme doctrine of Emancipation may be summarized by saying that all things are eternally immersed in Nirvāṇa...” [p. 351]. But how does the doctrine of Shunyata posit an Absolute as the source and support of phenomena and how does it allow a “One in All” or “All in One”?
The phrase “source and support of phenomena” sounds like your Overmind, which is the support of the Cosmos. Perhaps someone had some such perception while experiencing the silence leading to Nirvana.
How is this Absolute different from the Absolute of the Vedanta? or this emancipation different from the Vedantic mukti? If it were so, there would never have been all this quarrel between Buddhism and the Vedantic schools. It must be a new-fangled version of Buddhism or else it was a later development in which Buddhism reduced itself back to Adwaita.
The phrase “all things are eternally immersed in Nirvāṇa” seems to me at once bold and beautiful and gives an idea of the Silence. From this it is clearer that the realisation of Nirvana, if put in your terminology, is just the realisation of the Silence behind the Cosmos – from which Overmind would be two or three steps. But by “renouncing their right to pass on to a still Higher Evolution” they have managed to miss Overmind for two or three thousand years.
Yes. But is this Higher Evolution really a Buddhistic idea or only a European version of what Nirvana might be?
[Largest or earliest found passage: ] Sri Aurobindo. Letters on Himself and the Ashram // CWSA.- Volume 35. (≈ 26 vol. of SABCL).- Pondicherry: Sri Aurobindo Ashram, 2011.- 658 p.
Sri Aurobindo. Letters on Yoga // SABCL.- Volume 22. (≈ 28 vol. of CWSA).- Pondicherry: Sri Aurobindo Ashram, 1971.- 502 p.