Sri Aurobindo
Letters of Sri Aurobindo
5. Planes and Parts of the Being
The “Mind” in the ordinary use of the word covers indiscriminately the whole consciousness, for man is a mental being and mentalises everything; but in the language of this yoga the words “mind” and “mental” are used to connote specially the part of the nature which has to do with cognition and intelligence, with ideas, with mental or thought perceptions, the reactions of thought to things, with the truly mental movements and formations, mental vision and will, etc., that are part of his intelligence. 
The vital has to be carefully distinguished from mind, even though it has a mind element transfused into it; the vital is the Life-nature made up of desires, sensations, feelings, passions, energies of action, will of desire, reactions of the desire-soul in man and of all that play of possessive and other related instincts, anger, fear, greed, lust, etc., that belong to this field of the nature. Mind and vital are mixed up on the surface of the consciousness, but they are quite separate forces in themselves and as soon as one gets behind the ordinary surface consciousness one sees them as separate, discovers their distinction and can with the aid of this knowledge analyse their surface mixtures. It is quite possible and even usual during a time shorter or longer, sometimes very long, for the mind to accept the Divine or the yogic ideal while the vital is unconvinced and unsurrendered and goes obstinately on its way of desire, passion and attraction to the ordinary life. Their division or their conflict is the cause of most of the more acute difficulties of the sadhana.