Sri Aurobindo
Letters of Sri Aurobindo
Volume II - Part 1
The first step is a quiet mind – silence is a farther step, but quietude must be there, and by a quiet mind I mean a mental consciousness within which sees thoughts arrive to it and move about, but does not itself feel that it is thinking or identify itself with the thoughts or call them its own. Thoughts, mental 
movements may pass through it as wayfarers appear and pass from elsewhere through a silent country – the quiet mind observes them or does not care to observe them but in either case does not become active or lose its quietude. Silence is more than quietude; it can be gained by banishing thought altogether from the inner mind keeping it voiceless or quite outside; but more easily it is established by a descent from above – one feels it coming down, entering and occupying, or surrounding the personal consciousness which then tends to merge itself in the vast impersonal silence.