Whereas the first cause of impurity is related to the mixing of the vital force of desire into the action of the higher reason, the second is caused by the mixing of the sense-mind into the higher understanding. The sense-mind collects and interprets the impressions of the senses. Unfortunately, the sense-impressions frequently convey inaccurate, incomplete or mis-perceived facts. For instance, the senses tell us that the sun revolves around the earth. For long ages of human history, most people accepted this as factual. Today through the use of instruments of technology we are able to correct this false impression and override it with our reason. Along the way, those, such as Copernicus or Galileo who proposed a different model of the cosmic plan than that accepted by the sense-mind as reality, were treated with contempt and harsh punishment for their “heresy”.
Sri Aurobindo observes: “No knowledge can be true knowledge which subjects itself to the senses or uses them otherwise than as first indices whose data have constantly to be corrected and overpassed. The beginning of Science is the examination of the truths of the world-force that underlie its apparent workings such as our senses represent them to be; the beginning of philosophy is the examination of the principles of things which the senses mistranslate to us; the beginning of spiritual knowledge is the refusal to accept the limitations of the sense-life or to take the visible and sensible as anything more than phenomenon of the Reality.”
It becomes therefore essential that the higher reason and faculties of understanding are freed from subjection to the sense-mind and allowed to undertake their true function in a state of calm, quiet and an undemanding poise of the sense-mind. This practice is an important part of the Yoga of knowledge: “When the understanding in us stands back from the action of the sense-mind and repels its intermiscence, the latter detaches itself from the understanding and can be watched in its separate action. It then reveals itself as a constantly swirling and eddying undercurrent of habitual concepts, associations, perceptions, desires without any real sequence, order or principle of light….Ordinarily the human understanding accepts this undercurrent and tries to reduce it to a partial order and sequence; but by so doing it becomes itself subject to it and partakes of that disorder, restlessness, unintelligent subjection to habit and blind purposeless repetition which makes the ordinary human reason a misleading, limited and even frivolous and futile instrument. There is nothing to be done with this fickle, restless, violent and disturbing factor but to get rid of it whether by detaching it and then reducing it to stillness or by giving a concentration and singleness to the thought by which it will of itself reject this alien and confusing element.”
Sri Aurobindo, The Synthesis of Yoga, Part Two: The Yoga of Integral Knowledge, Chapter 3, The Purified Understanding, pp. 299-300