The buddhi–usually translated “intellect” or “intelligence”–embraces intellect, understanding, and reason. It is the higher, thinking mind which is the seat of wisdom. The manas is completely material in orientation, whereas the buddhi can enter into communication with the Self and be so transmuted by such contact that it virtually becomes spirit. That is why Krishna speaks three times of Buddhi Yoga in the Gita (2:39, 49; 10:10).
Truly the manas, the lower mind, is “like the troubled sea, when it cannot rest, whose waters cast up mire and dirt” (Isaiah 57:20). But the yogi’s buddhi can become steady through the Buddhi Yoga outlined by Krishna in the Bhagavad Gita:
“This buddhi yoga taught by Sankhya is now declared to you, so heed. Yoked to this buddhi yoga, you shall avoid the bonds of karma. In this no effort is lost, nor are adverse results produced. Even a little of this dharma protects from great fear. In this matter there is a single, resolute understanding. The thoughts of the irresolute are many-branched, truly endless” (Bhagavad Gita 2:39-41).
“Action is inferior by far to buddhi yoga. Seek refuge in enlightenment; pitiable are those who are motivated by action’s fruit. He who abides in the buddhi casts off here in this world both good and evil deeds. Therefore, yoke yourself to yoga. [This is a play on words since “yoke” and “yoga” have the same root: yuj.] Yoga is skill in action. Those who are truly established in the buddhi, the wise ones, having abandoned the fruits of action, freed from the bondage of rebirth, go to the place that is free from pain. When your buddhi crosses beyond the mire of delusion, then you shall be disgusted with the to-be-heard and what has been heard. When your buddhi stands, fixed in deep meditation, unmoving, disregarding the Vedic ritual-centered perspective, then you will attain yoga (union)” (Bhagavad Gita 2:49-53).
“To them, the constantly steadfast, worshipping me with affection, I bestow the buddhi yoga by which they come to me. Out of compassion for them, I, abiding in their own Selves, destroy the darkness born of ignorance by the shining lamp of knowledge” (Bhagavad Gita 10:10-11).
Buddhi Yoga is that which develops the buddhi, the intellect, which in time evolves the faculty of intuition, becoming both intellectual and intuitional. This is the mark of a fully developed human being.
Next in Living the Yoga Life: True Masters (And Not)