The reasoning intellect begins its process by a process of observation of external facts through the sense-organs. From these facts, it applies the faculties of organization, classification, memory and logic. It then comes to conclusions built up as a result of this process, and the longer it goes on, and the more facts it receives and analysis it undertakes, the more complete picture is assembled.
An example is the rising and setting of the sun. The facts of observation lead to a first conclusion that the earth is at the center and the sun revolves around it. For many millenia this conclusion was considered to be truth by the mind. Over time, however, with more facts and more detailed observations, including the development of various astronomical instruments,and the correlation of observations such as phases of the moon, eclipses and the cycle of the seasons, it became clear to the intellect that there must be something more involved, and eventually, it was determined, through application of reason, potentially with flashes of intuition, that actually the earth both rotates on its own axis and revolves around the sun, with the sun being at the center; in other words, the opposite of the first conclusion drawn on the basis of observable “facts”.
The gnosis, based on a different plane of consciousness, follows a different methodology. Sri Aurobindo observes: “The gnosis starts from the truth and shows the appearances in the light of the truth, it is itself the body of the truth and its spirit. The reason proceeds by inference, it concludes; but the gnosis proceeds by identity or vision,–it is, sees and knows. As directly as the physical vision sees and grasps the appearances of objects, so and far more directly the gnosis sees and grasps the truth of things. But where the physical sense gets into relation with objects by a veiled contact, the gnosis gets into identity with things by an unveiled oneness. Thus it is able to know all things as a man knows his own existence, simply, convincingly, directly.”
“Fundamentally, this is the difference between these two powers that the mental reason proceeds with labour from ignorance to truth, but the gnosis has in itself the direct contact, the immediate vision, the easy and constant possession of the truth and has no need of seeking or any kind of procedure.”
“Therefore the truth gained by the intellect is an acquisition over which there hangs always a certain shadow of doubt, an incompleteness, a surrounding penumbra of night and ignorance or half-knowledge, a possibility of alteration or annullation by farther knowledge. The truth of the gnosis is free from doubt, self-evident, self-existent, irrefragable, absolute.”
Sri Aurobindo, The Synthesis of Yoga, Part Two: The Yoga of Integral Knowledge, Chapter 22, Vijnana or Gnosis, pp. 462-463