As the Buddhi begins to develop and express itself in the human being, its first action is necessarily directly tied to the input and demands of the sense-mind and the desire-soul. This initial activity thus applies the power of reasoning, thought and will toward understanding and response to the sense-impressions and the fulfillment of the desires, cravings and other motives of the outer being as presented to it by the Manas, or sense-mind. This however is not the sum total of the capabilities of the Buddhi, and does not reflect the true meaning or purpose of the Buddhi.
Sri Aurobindo observes: “But the man whose reason and will are led and dominated by the lower mind, is an inferior type of human nature, and the part of our conscious being which consents to this domination is the lowest part of our manhood. The higher action of the Buddhi is to exceed and control the lower mind, not indeed to get rid of it, but to raise all the action of which it is the first suggestion into the nobler plane of will and intelligence. The impressions of the sense-mind are used by a thought which exceeds them and which arrives at truths they do not give, ideative truths of thought, truths of philosophy and science; a thinking, discovering, philosophic mind overcomes, rectifies and dominates the first mind of sense impressions. The impulsive reactive sensational mentality, the life-cravings and the mind of emotional desire are taken up by the intelligent will and are overcome, are rectified and dominated by a greater ethical mind which discovers and sets over them a law of right impulse, right desire, right emotion and right action. The receptive, crudely enjoying sensational mentality, the emotional mind and life mind are taken up by the intelligence and are overcome, rectified and dominated by a deeper, happier aesthetic mind which discovers and sets above them a law of true delight and beauty. All these new formations are used by a general Power of the intellectual, thinking and willing man in a soul of governing intellect, imagination, judgment, memory, volition, discerning reason and ideal feeling which uses them for knowledge, self-development, experience, discovery, creation, effectuation, aspires, strives, inwardly attains, endeavours to make a higher thing of the life of the soul in Nature. The primitive desire-soul no longer governs the being. It is still a desire-soul, but it is repressed and governed by a higher power, something which has manifested in itself the godheads of Truth, Will, Good, Beauty and tries to subject life to them. The crude desire-soul and mind is trying to convert itself into an ideal soul and mind, and the proportion in which some effect and harmony of this greater conscious being has been found and enthroned, is the measure of our increasing humanity.”
Sri Aurobindo, The Synthesis of Yoga, Part Four: The Yoga of Self-Perfection, Chapter 7, Purification–Intelligence and Will, pp. 640-641