Sri Aurobindo
Letters on Yoga
5. Planes and Parts of the Being
The mental being within watches, observes and passes judgment on all that happens in you. The psychic does not watch and observe in this way like a witness, but it feels and knows spontaneously in a much more direct and luminous way, by the very purity of its own nature and the divine instinct within it, and so, whenever it comes to the front it reveals at once what are the right and what the wrong movements in your nature.
The being of man is composed of these elements – the psychic behind supporting all, the inner mental, vital and physical, and the outer, quite external nature of mind, life and body which is their instrument of expression. But above all is the central being (Jivatma) which uses them all for its manifestation: it is a portion of the Divine Self; but this reality of himself is 
hidden from the external man who replaces this inmost self and soul of him by the mental and vital ego. It is only those who have begun to know themselves that become aware of their true central being; but still it is always there standing behind the action of mind, life and body and is most directly represented by the psychic which is itself a spark of the Divine. It is by the growth of the psychic element in one’s nature that one begins to come into conscious touch with one’s central being above. When that happens and the central being uses a conscious will to control and organize the movements of the nature, it is then that one has a real, a spiritual as opposed to a partial and merely mental or moral self-mastery.
Current publication:
Sri Aurobindo. Letters on Yoga // SABCL.- Volume 22. (≈ 28 vol. of CWSA).- Pondicherry: Sri Aurobindo Ashram, 1971.- 502 p.
Other publications:
1. 9848.
Sri Aurobindo. Letters on Yoga. I // CWSA.- Volume 28. (≈ 22 vol. of SABCL).- Pondicherry: Sri Aurobindo Ashram, 2012.- 590 p.
2. 22964.
Sri Aurobindo. Lights on Yoga [: Extracts from letters] / Reprint April 1977; First Edition: 1935.– Pondicherry: Sri Aurobindo Ashram, 1977.– 104 p.