There are four sources of knowledge: instinct, reason, intuition and super intuition or Brahmajnana.
When an ant crawls on your right arm, the left arm automatically moves towards the right arm to drive away the ant. The mind does not reason there. When you see a scorpion in front of your leg, you withdraw your leg automatically. This is termed instinctive or automatic movement. As you cross a street, how instinctively you move your body to save yourself from the cars! There is no vritti in such mechanical movement.
Instinct is found in animals and birds. In birds, the ego does not interfere with the free divine flow and divine play. Hence the work done by them through their instincts is more perfect than that done by human beings. Have you not noticed the excellent work done by birds in their building of wonderful nests?
Reason is higher than instinct and is found only in human beings. It collects facts, generalizes, reasons out from cause to effect, from effect to cause, from premises to conclusions, from propositions to proofs. It concludes, decides and comes to judgment. It takes you safely to the door of intuition and leaves you there.
Belief, reasoning, knowledge and faith are the four important psychic processes. First you have belief in a doctor. You go to him for diagnosis and treatment. He makes a thorough examination and then prescribes certain medicines. You take them. You reason out: Such and such is the disease. The doctor has given me iron and iodide. Iron will improve my blood. The iodide will stimulate the lymphatics and absorb the exudation and growth in the liver. So I should take it.
The disease is cured, by a course of these drugs, in a month. You get knowledge of and perfect faith in the efficacy of the medicine and the proficiency of the doctor. Then you recommend this doctor and his drugs to your friends.
Intuition is spiritual anubhava, experience. Knowledge through the functioning of the karana sarira, causal body, is intuition. Sri Aurobindo calls it the supermind or supramental consciousness. There is direct perception of truth, pratyaksha, or immediate knowledge through samadhi. You know things by a flash.
Professor Bergson preached about intuition in France to make people understand that there is another higher source of knowledge than intellect. In intuition, there is no reasoning process at all. Intuition transcends reason, but does not contradict it. Intellect takes one to the door of intuition and returns back. Intuition is divyadrishti, divine vision. It is jnana chakshus, the eye of wisdom. Spiritual flashes and glimpses of truth come through intuition. Inspiration, revelation, spiritual insight come through intuition.
Atmajnana is above intuition. It transcends the karana sarira, the causal body. It is the highest form of knowledge. It is the only reality.