The Theory of Forms or Theory of Ideas, also known as Platonic idealism or Platonic realism, is a philosophical theory credited to the Classical Greek philosopher Plato.
The central image from Raphael's The School of Athens (1509–1511), depicting Plato (left) and Aristotle (right). Plato is depicted pointing upwards, in reference to his belief in the higher Forms, while Aristotle disagrees and gestures downwards to the here-and-now, in reference to his belief in empiricism.
Plato's unwritten doctrines are metaphysical theories ascribed to him by his students and other ancient philosophers but not clearly formulated in his writings. In recent research, they are sometimes
Aristotle referred to Plato's 'unwritten doctrines' and discussed Plato's principle theory.
Papirus Oxyrhynchus, with fragment of Plato's Republic
The beginning of the Seventh Letter in the oldest, surviving manuscript from the ninth century CE (Paris, Bibliothèque Nationale, Gr. 1807)
Aristotle, his student Theophrastus, and Strato of Lampsacus (National and Kapodistrian University of Athens)