"Yoga is the inhibition of the functions of the mind," says Patanjali. The functions of the mind must be suppressed, and in order that we may be able to follow out really what this means, we must go more closely into what the Indian philosopher means by the word "mind".
Mind, in the wide sense of the term, has three great properties or qualities: cognition, desire or will, activity. Now Yoga is not immediately concerned with all these three, but only with one, cognition, the Samkhyan subject. But you cannot separate cognition, as we have seen, completely from the others, because consciousness is a unit, and although we are only concerned with that part of consciousness which we specifically call cognition, we cannot get cognition all by itself. Hence the Indian psychologist investigating this property, cognition, divides it up into three or, as the Vedanta says, into four (with all submission, the Vedantin here makes a mistake). If you take up any Vedantic book and read about mind, you will find a particular word used for it which. translated, means "internal organ". This antah-karana is the word always used where in English we use "mind"; but it is only used in relation to cognition, not in relation to activity and desire. It is said to be fourfold, being made up of Manas, Buddhi, Ahamkara, and Chitta; but this fourfold division is a very curious division. We know what Manas is, what Buddhi is, what Ahamkara is, but what is this Chitta? What is Chitta, outside Manas, Buddhi and Ahamkara? Ask anyone you like. and record his answer; you will find that it is of the vaguest kind. Let us try to analyse it for ourselves, and see whether light will come upon it by using the Theosophic idea of a triplet summed up in a fourth, that is not really a fourth, but the summation of the three. Manas, Buddhi and Ahamkara are the three different sides of a triangle,' which triangle is called Chitta. The Chitta is not a fourth, but the sum of the three: Manas, Buddhi and Ahamkara. This is the old idea of a trinity in unity. Over and over again H. P. Blavatsky uses this summation as a fourth to her triplets, for she follows the old methods. The fourth, which sums up the three but is not other than they, makes a unity out of their apparent diversity. Let us apply that to Antahkarana.
Take cognition. Though in cognition that aspect of the Self is predominant, yet it cannot exist absolutely alone, The whole Self is there in every act of cognition. Similarly with the other two. One cannot exist separate from the others. Where there is cognition the other two are present, though subordinate to it. The activity is there, the will is there. Let us think of cognition as pure as it can be, turned on itself, reflected in itself, and we have Buddhi, the pure reason, the very essence of cognition; this in the universe is represented by Vishnu, the sustaining wisdom of the universe. Now let us think of cognition looking outwards, and as reflecting itself in activity, its brother quality, and we have a mixture of cognition and activity which is called Manas, the active mind; cognition reflected in activity is Manas in man or Brahma, the creative mind, in the universe. When cognition similarly reflects itself in will, then it becomes Ahamkara, the "I am I" in man, represented by Mahadeva in the universe. Thus wee have found within the limits of this cognition a triple division, making up the internal organ or Antahkarana--Manas, plus Buddhi, plus Ahamkara--and we can find no fourth. What is then Chitta? It is the summation of the three, the three taken together, the totality of the three. Because of the old way of counting these things, you get this division of Antahkarana into four.