Platonism is the philosophy of Plato and philosophical systems closely derived from it, considered the opposite of nominalism, or anti-realism. Platonism has had a profound influence on Western thought. Platonism or Platonic realism affirms the real existence of forms or abstract objects, originally to solve the problem of universals. Abstract objects are asserted to exist in a third realm distinct from both the sensible external world and from the internal world of consciousness. This can apply to properties, types, propositions, meanings, numbers, sets, truth values, and so on (see abstract object theory).
Plato's doctrine originally was an attempt to reconcile the reality which is perceptible but unintelligible, associated with the flux of Heraclitus and studied by the likes of physical science, and the reality which is imperceptible but intelligible, associated with the unchanging being of Parmenides and studied by the likes of mathematics. Geometry was the main motivation of Plato, and this also shows the influence of Pythagoras. The Forms are typically described in dialogues such as the Phaedo, Symposium and Republic as perfect archetypes of which objects in the everyday world are imperfect copies. Aristotle's Third Man Argument is its most famous criticism in antiquity.
