ymbolizes for Plato the physical world of appearances. Escape into the sun-filled setting outside the cave symbolizes the transition to the real world, the world of full and perfect being, the world of Forms, which is the proper object of knowledge.Nature of FormsThe theory of Forms may best be understood in terms of mathematical entities. For Plato, therefore, the Form "circularity" exists, but not in the physical world of space and time. It exists as a changeless object in the world of Forms or Ideas, which can be known only by reason. Forms have greater reality than objects in the physical world both because of their perfection and stability and because they are models, resemblance to which gives ordinary physical objects whatever reality they have. Circularity, squareness, and triangularity are excellent examples, then, of what Plato meant by Forms. An object existing in the physical world may be called a circle or a square or a triangle only to the extent that it resembles ("participates in" is Plato's phrase) the Form "circularity" or "squareness" or "triangularity."Plato extended his theory beyond the realm of mathematics. An object is beautiful to the extent that it participates in the Idea, or Form, of beauty. Everything in the world of space and time is what it is by virtue of its resemblance to, or participation in, its universal Form. The ability to define the universal term is evidence that one has grasped the Form to which that universal refers.Plato conceived the Forms as arranged hierarchically; the supreme Form is the Form of the Good, which, like the sun in the myth of the cave, illuminates all the other Ideas. In philosophical language, Plato's theory of Forms is both an epistemological (theory of knowledge) and an ontological (theory of being) thesis.Political Theory The Republic, Plato's major political work, is concerned with the question of justice and therefore with the questions "what is a just state" and "who ...
