The mind may be likened to a great sea upon which there are visible a few islands. The islands represent the conscious thoughts — consciousness we use to calculate, to map out our plans, to form our judgments. This is the mind that for centuries was accepted as the entire mind. But we know that the islands are merely the tops of huge mountain-ranges formed by the floor of the sea in mighty, permanent upheaval; that as this sea-floor rises, high above its customary level, and thrusts its bulk above the waters into the atmosphere, is possibly the island.
There can be no consciousness except as that which is already in the mind – the vast subconscious material of all experience rises into view and relates itself through the senses to an outside world. So our recognition of the impression is merely the rising into consciousness of the subconscious material in response to a stimulus from the outside world which appeals through the senses. The visible island is but a symbol of the submarine mountain. The present mental impression is but proof of a great bulk of past experiences.