4408. The existence of a correspondence between the sight of the eye and that of the understanding is perfectly plain to those who stop to reflect, since the objects that make up the world, each of which derives something from the light of the sun, come in through the eye and store themselves in the memory. They deposit themselves there as visual impressions of those objects, for the things which a person recalls from the memory are seen inwardly by him. They are the source of man's formation of mental images, whose constituent ideas philosophers term material ideas. And when a person sees these objects even more inwardly within himself they present themselves as thought, doing so again as something like visual impressions, though purer ones, whose constituent ideas are called immaterial, and also intellectual. The existence of an interior light holding life, and therefore intelligence and wisdom, within it, which provides the light for the interior sight and meets those impressions which have come in through the external sight, is plainly evident, as also is the fact that the action of the interior light is dependent on the way in which things that are present there from the light of the world are deployed. The things which come in through hearing are also converted inwardly into impressions similar to the visual ones which are formed from the light of the world.