The comment that the Socratic philosopher must "return to the cave" is a reference to the allegory of the cave in The Republic and emphasizes that the philosopher must return to the cave to understand the relationship between the ideal and its projection in this world. Plato's conception of the existence of Forms as the ideals of the imperfect objects and ideas of this world derived in part from the ongoing discussion in Greek philosophy over change versus permanence. The allegory also relates to issues of epistemology as to what we can know and how we can know it. The cave becomes the touchstone, the example that serves to demonstrate the relationship between the idea and the reality, between perception and reality, between the perfection of the idea and the imperfection of the reality.
Plato addressed the issue of change by making a distinction between the imperfect material world and the changeless world of forms. This world, the world of the senses, is subject to change, but it is only the shadow of the changeless world of forms. Plato presented this idea graphically in the allegory of the cave in The Republic, where the shadows on the walls represented the imperfect likeness of the perfection of the real objects, much as the real world in which we live is only a reflection of the world of forms. This is Plato's cosmology, and it requires the Forms, the particulars modeled on those forms, and the agent who does the modelling, the Craftsman. Order is imposed on the formless reality of this world by the Craftsman, and this occurs as the four basic elements are mixed in varying proportions to form the matter of this world. These four elements are themselves unchanged--fire, air, water, and earth. He agreed with the atomists that the varieties of sensible objects came from the differences in the shapes and sizes of the particles of which they were composed, but he saw these primary solids as in turn made up of polyhedrons ...