Sri Aurobindo
Letters on Yoga
5. Planes and Parts of the Being
Fragment ID: 437
The mind proper is divided into three parts – thinking Mind, dynamic Mind, externalising Mind – the former concerned with ideas and knowledge in their own right, the second with the putting out of mental forces for realisation of the idea, the third with the expression of them in life (not only by speech, but by any form it can give). The word “physical mind” is rather ambiguous, because it can mean this externalising Mind and the mental in the physical taken together.
Vital Mind proper is a sort of a mediator between vital emotion, desire, impulsion, etc. and the mental proper. It expresses the desires, feelings, emotions, passions, ambitions, possessive and active tendencies of the vital and throws them into mental forms (the pure imaginations or dreams of greatness, happiness, etc. in which men indulge are one peculiar form of the vital-mind activity). There is still a lower stage of the mental in the vital which merely expresses the vital stuff without subjecting it to any play of intelligence. It is through this mental vital that the vital passions, impulses, desires rise up and get into the Buddhi and either cloud or distort it.
As the vital Mind is limited by the vital view and feeling of things (while the dynamic Intelligence is not, for it acts by the idea and reason), so the mind in the physical or mental physical is limited by the physical view and experience of things, it mentalises the experiences brought by the contacts of outward life 
and things, and does not go beyond that (though it can do that much very cleverly), unlike the externalising mind which deals with them more from the reason and its higher intelligence. But in practice these two usually get mixed together. The mechanical mind is a much lower action of the mental physical which, left to itself, would only repeat customary ideas and record the natural reflexes of the physical consciousness to the contacts of outward life and things.
The lower vital as distinguished from the higher is concerned only with the small greeds, small desires, small passions, etc. which make up the daily stuff of life for the ordinary sensational man – while the vital-physical proper is the nervous being giving vital reflexes to contacts of things with the physical consciousness.
Current publication:
Sri Aurobindo. Letters on Yoga // SABCL.- Volume 22. (≈ 28 vol. of CWSA).- Pondicherry: Sri Aurobindo Ashram, 1971.- 502 p.
Other publications: