Sri Aurobindo
Letters on Yoga
5. Planes and Parts of the Being
The supermind is the One Truth deploying and determining the manifestation of its Powers – all these Powers working as a 
multiple Oneness, in harmony, without opposition or collision, according to the One Will inherent in all. The overmind takes these Truths and Powers and sets each working as a force in itself with its necessary consequences – there can be harmony in their action, but it is rather synthetic and mostly partial than inherent and inevitable and as one descends from the highest overmind, separation, collision and conflict of forces increase, separability dominates, ignorance grows, existence becomes a clash of possibilities, a mixture of conflicting half-truths, an unsolved and apparently unsolvable riddle and puzzle.
Current publication:
Sri Aurobindo. Letters on Yoga // SABCL.- Volume 22. (≈ 28 vol. of CWSA).- Pondicherry: Sri Aurobindo Ashram, 1971.- 502 p.
Other publications:
1. 10002.
Sri Aurobindo. Letters on Yoga. I // CWSA.- Volume 28. (≈ 22 vol. of SABCL).- Pondicherry: Sri Aurobindo Ashram, 2012.- 590 p.
2. 20431.
Sri Aurobindo. Letters of Sri Aurobindo: In 4 Series.- First Series [On Yoga].- Bombay: Sri Aurobindo Sircle, 1947.- 416 p.