Plato's greatest contribution to modern society is found in his theories relating to metaphysics. These is now referred to as Platonism (or Exaggerated Realism). Plato divides his world into two aspects: the intelligible world and the perceptual world.
The Perceptual world: Plato saw the perceptual world around us as imperfect copies of the intelligible forms or ideas.
The Intelligible world: Forms are unchangeable and perfect, and only comprehensible by the use of intellect and understanding. For example, a triangle belongs to the world of forms, since we can reason out its properties (angles always equal to 180 degrees, for example), using our intellect. Imagination, though, is part of the perceptual world, since it is not concrete and unchanging for each person.
Nature of Knowledge and Learning:
Plato's ideas on knowledge has survived throughout the ages and is still relevant in today's society. Today it has come to be known as Platonic epistemology.
Platonic Epistemology: Plato believed that knowledge is innate, or inborn, and that the development of ideas buried deep in the soul, and may be guided out by teachers. Plato drew a sharp distinction between knowledge, which is certain, and mere opinion. Opinions derive from the shifting world of sensation -- knowledge derives from the world of timeless Forms, or essences.
The Analogy of the Cave: In his best-known dialogue, "The Republic", Plato drew an analogy between human sensation and the shadows that pass along the wall of a ca ve. He tells his audience to imagine a group of people tied up, facing the wall of a cave. They are unable to move, and see only the shadows of the real objects. Supposing a prisoner was taken from the cave and shown the real world. At first he would doubt what he saw, preferring his earlier knowledge.