At the stage of human evolution, we see the emergence of a self-consciousness (ego-sense, called ahamkara in the texts) and a discriminating intellect and will, called Buddhi in the Sanskrit literature. The nature of Buddhi indicates the active presence of the quality or mode of sattwa, bringing light and intelligence into the action of the gunas. Tamas and rajas remain active, and in fact, can color the action of the intelligent will by encouraging it to justify whatever desire or line of action happens to occur.
Some people believe that the action of the intelligent, self-conscious intellect gives the human being “free will”. Others point out, as the Gita itself does, that the mixed action of sattva along with rajas and tamas shows that the human being in its normal state is still subject to the Gunas of Nature and thus, does not actually exhibit free will in its ultimate sense.
Sri Aurobindo takes up the discussion: “Man is not like the tiger or the fire or the storm; he cannot kill and say as a sufficient justification, ‘I am acting according to my nature’, and he cannot do it, because he has not the nature and not, therefore, the law of action, svadharma, of the tiger, storm or fire. He has a conscious intelligent will, a buddhi, and to that he must refer his actions. If he does not do so, if he acts blindly according to his impulses and passions, then the law of his being is not rightly worked out…, he has not acted according to the full measure of his humanity, but even as might the animal.”
“…in man sattva is awake and acts not only as intelligence and intelligent will, but as a seeking for light, for right knowledge and right action according to that knowledge, as a sympathetic perception of the existence and claims of others, as an attempt to know the higher law of his own nature, which the sattwic principle in him creates, and to obey it, and as a conception of the greater peace and happiness which virtue, knowledge and sympathy bring in their train. he knows more or less imperfectly that he has to govern his rajasic and tamasic by his sattwic nature and that thither tends the perfection of his normal humanity.”
Sri Aurobindo, Essays on the Gita, First Series, Chapter 21, The Determinism of Nature, pp. 210-211