“Buddhi is a construction of conscious being which quite exceeds its beginnings in the basic chitta; it is the intelligence with its power of knowledge and will. Buddhi takes up and deals with all the rest of the action of the mind and life and body. It is in its nature thought-power and will-power of the Spirit turned into the lower form of a mental activity. We may distinguish three successive gradations of the action of this intelligence. There is first an inferior perceptive understanding which simply takes up, records, understands and responds to the communications of the sense-mind, memory, heart and sensational mentality. It creates by their means an elementary thinking mind which does not go beyond their data, but subjects itself to their mould and rings out their repetitions, runs round and round in the habitual circle of thought and will suggested by them or follows, with an obedient subservience of the reason to the suggestions of life, any fresh determinations which may be offered to its perception and conception. Beyond this elementary understanding, which we all use to an enormous extent, there is a power of arranging or selecting reason and will-force of the intelligence which has for its action and aim an attempt to arrive at a plausible, sufficient, settled ordering of knowledge and will for the use of an intellectual conception of life.
In spite of its more purely intellectual character this secondary or intermediate reason is really pragmatic in its intention. It creates a certain kind of intellectual structure, frame, rule into which it tries to cast the inner and outer life so as to use it with a certain mastery and government for the purposes of some kind of rational will. It is this reason which gives to our normal intellectual being our set aesthetic and ethical standards, our structures of opinion and our established norms of idea and purpose. It is highly developed and takes the primacy in all men of an at all developed understanding. But beyond it there is a reason, a highest action of the buddhi which concerns itself disinterestedly with a pursuit of pure truth and right knowledge; it seeks to discover the real Truth behind life and things and our apparent selves and to subject its will to the law of Truth. Few, if any of us, can use this highest reason with any purity, but the attempt to do it is the topmost capacity of the inner instrument, the antaḥkaraṇa.
Buddhi is really an intermediary between a much higher Truth-mind not now in our active possession, which is the direct instrument of Spirit, and the physical life of the human mind evolved in body.”
- The Synthesis of Yoga, p.652, “The Instruments of the Spirit”