Sri Aurobindo
Letters of Sri Aurobindo
Volume I - Part 2
It depends on what is meant by the higher buddhi – whether you use the word to mean the higher part of the intellect or the higher Mind. The higher Mind in itself on its own level knows, but when it is involved in the ordinary human intelligence and works under limitations, it often does not know – or it has the 
idea merely that it must be so but has not the consciousness of its separate existence. The intellect can rise above its ordinary movements and feel itself as a separate power no longer working under the limitations of the vital and physical mind and the senses. It then begins to reflect something of the action of the higher mind but without the full freedom and greater light and truth of the higher mind.