- 1 What is Mental Silence?
- 2 2. Benefits of practising Mental Silence
- 3 3. Prerequisites for Attaining Mental Silence
- 4 4. Challenges
- 5 5. How to Achieve/Practice Mental Silence?
What is Mental Silence?
The stillness of the mind means, first, the falling to rest of the habitual thought movements, thought formations, thought currents which agitate this mind-substance. That repose, vacancy of movement, is for many a sufficient mental silence. 
The Experience of Mental Silence
But it is possible also to pass to that through a certain experience of Nirvana, an absolute silence of mind and cessation of its activities, constructions, representations which can be so complete that not only to the silent mind but also to the passive senses the whole world is emptied of its solidity and reality and things appear only as unsubstantial forms without any real habitations or else floating in something that is a nameless Infinite: this Infinite or else something still beyond is That which alone is real; an absolute calm, peace, liberation would be the resulting state. Action would continue, but no initiation or participation in it by the silent liberated consciousness; a nameless Power would do all until there began the descent from above which would transform the consciousness, making its silence and freedom a basis for a luminous knowledge, action, Ananda. 
Observing Thoughts, Not Throwing Them Back
To silence the mind it is not enough to throw back each thought as it comes, that can only be a subordinate movement. One must get back from all thought and be separate from it, a silent consciousness observing the thoughts if they come, but not oneself thinking or identified with the thoughts. Thoughts must be felt as outside things altogether. It is then easier to reject thoughts or let them pass without their disturbing the quietude of the mind. 
2. Benefits of practising Mental Silence
Finding Solutions to Problems
When one has learned to silence the mind at will and to concentrate it in receptive silence, then there will be no problem that cannot be solved, no mental difficulty whose solution cannot be found. When it is agitated, thought becomes confused and impotent; in an attentive tranquillity, the light can manifest itself and open up new horizons to man's capacity. 
Divine Guidance for your Work
I am going to give you two examples to make you understand what true spontaneity is. One—you all know about it undoubtedly—is of the time Sri Aurobindo began writing the Arya, in 1914. It was neither a mental knowledge nor even a mental creation which he transcribed: he silenced his mind and sat at the typewriter, and from above, from the higher planes, all that had to be written came down, all ready, and he had only to move his fingers on the typewriter and it was transcribed. It was in this state of mental silence which allows the knowledge—and even the expression—from above to pass through that he wrote the whole Arya, with its sixty-four printed pages a month. This is why, besides, he could do it, for if it had been a mental work of construction it would have been quite impossible. 
To make yourself blank in meditation creates an inner silence; it does not mean that you have become nothing or have become a dead and inert mass. Making yourself an empty vessel, you invite that which shall fill it. It means that you release the stress of your inner consciousness towards realisation. The nature of the consciousness and the degree of its stress determine the forces that you bring into play and whether they shall help and fulfil or fail or even harm and hinder. 
This kind of revelation can only occur in a silent mind—at least in a mind that is at rest, completely quiet and still, otherwise they do not come. Or if they come, you do not notice them, because of all the noise you are making. And of course, they help this quiet, this silence, this receptivity to become better and better established. 
To hear it one should make oneself as silent and passive as possible. And if, in the mental silence, a part of the being can take the attitude of the witness who observes without reacting or participating, then one can take account of the effect which the music produces on the feelings and emotions; and if it produces a state of deep calm and of semi-trance, then that is quite good. 
Getting Better Quality of Sleep (conscious sleep)
The only cure for insomnia is to get rid of the need for sleep by knowing how to obtain mental silence at will. When you can obtain silence at will, you must put your body into a position of absolute repose, stretched out comfortably on the bed; then you go within yourself until there is perfect mental silence and enter a state that is something like a very deep sleep. 
3. Prerequisites for Attaining Mental Silence
Remember first that an inner quietude, caused by the purification of the restless mind and vital, is the first condition of a secure sadhana. Remember, next, that to feel the Mother's presence while in external action is already a great step and one that cannot be attained without a considerable inner progress. Probably, what you feel you need so much but cannot define is a constant and vivid sense of the Mother's force working in you, descending from above and taking possession of the different planes of your being. That is often a prior condition for the twofold movement of ascent and descent; it will surely come in time. These things can take a long time to begin visibly, especially when the mind is accustomed to be very active and has not the habit of mental silence. When that veiling activity is there, much work has to be carried on behind the mobile screen of the mind and the sadhak thinks nothing is happening when really much preparation is being done. If you want a more swift and visible progress, it can only be by bringing your psychic to the front through a constant self-offering. Aspire intensely, but without impatience. 
Misconception that one will Lose their Ability to Think
I emphasise this fact because there are quite a few people who, when mental silence has been transmitted to them by occult means, are immediately alarmed and afraid of losing their intelligence. Because they can no longer think, they fear they may become stupid! But to cease thinking is a much higher achievement than to be able to spin out thoughts endlessly and it demands a much greater development. 
Abolishing the Ego - Getting Rid of Moral Egoism
Downward Pull of Imperfections
… the spiritual emergence has to wait at each step for the instruments to be ready; next, as the spiritual formation emerges, it is mixed inextricably with the powers, motives, impulses of an imperfect mind, life and body,—there is a pull on it to accept and serve these powers, motives and impulses, a downward gravitation and perilous mixture, a constant temptation to fall or deviation, at least a fettering, a weight, a retardation; there is a necessity to return upon a step gained in order to bring up something of the nature which hangs back and prevents a farther step; finally, there is, by the very character of mind in which it has to work, a limitation of the emerging spiritual light and power and a compulsion on it to move by segments, to follow one line or another and leave altogether or leave till later on the achievement of its own totality. This hampering, this obstacle of the mind, life and body,—the heavy inertia and persistence of the body, the turbid passions of the life-part, the obscurity and doubting incertitudes, denials, other-formulations of the mind,—is an impediment so great and intolerable that the spiritual urge becomes impatient and tries rigorously to quell these opponents, to reject the life, to mortify the body, to silence the mind and achieve its own separate salvation, spirit departing into pure spirit and rejecting from it altogether an undivine and obscure Nature. 
When the inner action proceeds after the silence, even if it be then a more predominatingly intuitive thought and movement, the old powers will yet interfere, if not from within, then by a hundred suggestions from without, and an inferior mentality will mix in, will question or obstruct or will try to lay hold on the greater movement and to lower or darken or distort or minimise it in the process. Therefore the necessity of a process of elimination or transformation of the inferior mentality remains always imperative,—or perhaps both at once, an elimination of all that is native to the lower being, its disfiguring accidents, its depreciations of value, its distortions of substance and all else that the greater truth cannot harbour, and a transformation of the essential things our mind derives from the supermind and spirit but represents in the manner of the mental ignorance. 
5. How to Achieve/Practice Mental Silence?
What the sadhaka has to do is to be careful to reject and hush these outsiders, so that during the meditation at least the peace and quietude of the mind and vital may be complete. This can be done best if you keep a strong and silent will. 
Entering a Higher Domain
If you try to silence your mind directly, it is a hard job, almost impossible; for the most material part of the mind never stops its activity—it goes on and on like a non-stop recording machine. It repeats all that it records and unless there is a switch to stop it, it continues and continues indefinitely. If, on the other hand, you manage to shift your consciousness into a higher domain, above the ordinary mind, this opening to the Light calms the mind, it does not stir any longer, and the mental silence so obtained can become constant. Once you enter into this domain, you may very well never come out of it—the external mind always remains calm.
(Sri Aurobindo, 8th March 1951) 
If you want a more swift and visible progress, it can only be by bringing your psychic to the front through a constant self-offering. Aspire intensely, but without impatience. 
And if one carries this a little further, one should never think and plan beforehand what one ought to say or write. One should simply be able to silence one's mind, to turn it like a receptacle towards the higher Consciousness and express as it receives it, in mental silence, what comes from above. That would be true spontaneity. 
Take one of Sri Aurobindo's books. Read a sentence or two. Then remain silent and concentrated to understand the deeper meaning. Try to concentrate deeply enough to obtain mental silence and begin again daily until you obtain a result. 
There is a world of ideas without form and it is there that you must enter if you want to seize what is behind the words. So long as you have to draw your understanding from the forms of words, you are likely to fall into much confusion about the true sense; but if in a silence of your mind you can rise into the world from which ideas descend to take form, at once the real understanding comes. If you are to be sure of understanding one another, you must be able to understand in silence. There is a condition in which your minds are so well attuned and harmonised together that one perceives the thought of the other without any necessity of words. But if there is not this attunement, there will always be some deformation of your meaning, because to what you speak the other mind supplies its own significance. I use a word in a certain sense or shade of its sense; you are accustomed to put into it another sense or shade. Then, evidently, you will understand, not my exact meaning in it, but what the word means to you. This is true not of speech only, but of reading also. If you want to understand a book with a deep teaching in it, you must be able to read it in the mind's silence; you must wait and let the expression go deep inside you into the region where words are no more and from there come slowly back to your exterior consciousness and its surface understanding. But if you let the words jump at your external mind and try to adapt and adjust the two, you will have entirely missed their real sense and power. There can be no perfect understanding unless you are in union with the unexpressed mind that is behind the centre of expression. 
Witness Without Involvement