The Gita adopts the basic psychological framework of the Sankhya, which includes a higher intelligence, buddhi that becomes active in the human being and which provides the power of reasoning. Sri Aurobindo describes this power of buddhi: “It is the understanding power of his nature, buddhi, that chooses the work for him or, more often, approves and sets its sanction on one or other among the many suggestions of his complex instincts, impulsions, ideas and desires. It is that which determines for him what is right or wrong, to be done or not to be done, Dharma or Adharma. And the persistence of the will is that continuous force of mental Nature which sustains the work and gives it consistence and persistence.”
When we ordinarily speak about the higher intelligence or the power of Reason, we tend to look upon it as some kind of “unified” power that works similarly in all people. The Gita reminds us, however, that here, once again, the three Gunas are involved in the actual application of this power in any human individual. There is thus a “tamasic intelligence”, as well as a “rajasic intelligence” and a “sattwic intelligence.”. It should be remembered that the Gunas are constantly acting in all of us, and thus, at any point in time, any individual may be under the influence of one or another of these Gunas in any situation.
Sri Aurobindo describes the characteristics of these systematically, starting with the tamasic form: “The tamasic reason is a false, ignorant and darkened instrument which chains us to see all things in a dull and wrong light, a cloud of misconceptions, a stupid ignoring of the values of things and people. This reason calls light darkness and darkness light, takes what is not the true law and upholds it as the law, persists in the thing which ought not to be done and holds it up to us as the one right thing to be done. Its ignorance is invincible and its persistence of will is a persistence in the satisfaction and dull pride of its ignorance. That is on its side of blind action; but it is pursued also by a heavy stress of inertia and impotence, a persistence in dullness and sleep, an aversion to mental change and progress, a dwelling on the fears and pains and depressions of mind which deter us in our path or keep us to base, weak and cowardly ways. Timidity, shirking, evasion, indolence, the justification by the mind of its fears and false doubts and cautions and refusals of duty and its lapses and turnings from the call of our higher nature, a safe following of the line of least resistance so that there may be the least trouble and effort and peril in the winning of the fruit of our labour…these are characteristics of the tamasic will and intelligence.”
Sri Aurobindo, Essays on the Gita, Second Series, Part II, Chapter 19, The Gunas, Mind and Works, pp. 485-486